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Which diesel car to buy. How to test a used diesel engine before purchasing. Checking the condition of oil and antifreeze

The decision to buy a car with a diesel engine suggests the reasons why this option is chosen. The reasons determine the extent and main parameters of checking the engine before purchase. But the question of how to check a diesel engine when purchasing is the main one.

Diesel engine selection

Before coming to the dealership, you need to understand the basic characteristics that the engine of the car you are buying would have. There are no universal diesel engines, so desires must be linked together. An engine cannot be powerful and not actively consume oil, reliable and relatively cheap to maintain.

Powerful motors have a long service life and are reliable, but are not as economical as low-power engines, which are less reliable and have a shorter service life.

Engines without turbines are more reliable, but turbocharged diesel engines have better power characteristics with lower efficiency.

Having chosen an engine that suits the buyer in terms of its performance, you should understand the methodology for testing a diesel engine. The engine ultimately determines the fate of the car you buy.

Methodology for checking diesel engines during the car buying process

Having previously chosen a car with a diesel engine that suits your desires, you should begin to study the engine.

When purchasing a new car, the inspection method is simpler and consists of parts of the general method for a used car.

It is better to break the check down into steps.

At this step, it is necessary to inspect the diesel engine for the presence of fluid leaks characteristic of engine overheating. It is better if there are no drips on the seals and other inspected places.
It is necessary to remove the pipe that connects the air filter to the intake manifold, and if the diesel engine is turbocharged, then to the turbine. If traces of oil are found in the pipe, then wear is possible, which may be significant in the cylinder-piston group or, at best, the air filter is very dirty.
The diesel engine should be started, and if it does not start the first time, then there may be a hidden defect. Repeat starting the engine at different intervals without touching the gas pedal:
- Starting is normal, then at idle you need to watch the exhaust gases. A small emission of smoke is allowed when the engine is first started, but thereafter it should not be present in the exhaust gases.
- A quiet knocking sound when the diesel engine is running is acceptable, other sounds should be acceptable.
- At idle, you need to increase the speed to 3000-4000 per minute, twitching and vibration are not acceptable. The color of the exhaust should not be bluish, otherwise the ignition will be delayed or other inaccuracies in the unit settings.
- If you accelerate sharply at idle and at high speeds there is a bluish exhaust and vibration, then in these modes there will be a loss of power.
- If the exhaust is black and the engine is knocking, then you should not be interested in such a car any further.

Checking engine compression and other parameters

Sometimes, in addition to the method presented above, it is desirable to check some engine parameters using express methods that do not claim absolute accuracy. Sometimes these methods produce useful results.

It is advisable to check engine compression with a special device. For a diesel engine, the permissible value is 36 atmospheres, a minimum of 31 and the pressure spread across the cylinders is within two atmospheres.

If there is no device, then it is possible to evaluate the compression, at least by eye. You need to turn on the engine, carefully remove the diesel filler cap and simply place it on the neck. If the gases push the lid back, the compression is probably not normal. High-quality diagnostics are carried out only by specialists at service stations.

If you start the engine, the radiator is filled with antifreeze according to the norm, wait until the thermostat opens and watch whether or not air bubbles come out into the neck of the radiator with the engine running. The appearance of bubbles indicates damage to the cylinder block.

The condition of some diesel units can be approximately assessed by inspecting a running engine in a car.

To determine the condition of the piston system, it is necessary to sharply increase the speed to 3000 for 5 seconds on a heated unit; if the exhaust pipe does not smoke, then sharply increase the speed to 4200 and hold for 3 seconds. If there is no smoke, the piston system and turbine are operating normally.

But if there is smoke, there will be increased oil consumption. The more black smoke, the less traction performance.

Checking the injection pump pump comes down to determining the ability to start a warm engine; if it starts with voltage, then the pump is faulty.

An engine tested by the above methods should be considered conditionally tested; a thorough check is possible only in a service organization.

To the question of how to check a diesel engine when buying a car with maximum completeness, the answer is simple - you need to contact a service center.

Conclusion

Testing in real road conditions is the best test of a diesel engine, so when buying a car you need to test it on the road before making a final decision.

At different speeds, a diesel engine can behave differently, because these engines do not like high speeds. Choosing the optimal speed for the engine is important from the point of view of fuel consumption, oil consumption and wear of components.

Therefore, the choice of diesel engine must be approached carefully, having thought through how to use it.

Recently, diesel engines have gained wide popularity. They are installed in many cars, including compact city cars, huge SUVs and even sports cars. This is due to low fuel consumption.

Since diesel is ubiquitous, the aftermarket is flooded with such vehicles. And all potential car owners need to familiarize themselves with the rules for checking such cars before purchasing.

Which diesel is better to choose?

Initially, all potential motorists need to decide what exactly they want to get from their future car. Some give their preference to power, others to reliability and safety, and still others to low fuel consumption. It is the engines that are responsible for all these characteristics, and the other systems and mechanisms of the technical part play secondary roles.

When choosing an engine, you need to consider:

Small engines consume the least fuel;
Large engines are more reliable and durable in operation;
The presence of a turbine increases power characteristics;
The absence of a turbine simplifies the engine design, which has a positive effect on reliability and durability.

Taking into account the above points, you can approximately determine what engine size is suitable for you. However, for beginners, the data does not mean anything; they will need to choose the first vehicle based on luck. They will be able to determine which engine suits them only through practice, which was temporarily not enough.

How to check?

Once you have decided on the engine size, you will need to check it. You should not buy a diesel car without checking it, since the car can start and drive normally, even if there are problems.

Checks include the following steps:

Visual inspection. Any contamination is considered normal. During a visual inspection, you should only be interested in oil leaks. If any are present, it is recommended to refuse the purchase in favor of another option. Otherwise, you will soon have to go to a car workshop for repairs, or even completely change the engine.
Remove the pipe near the air filter. Its contamination indicates various problems. Minimal – air filter contamination. This problem can be solved by simply replacing the filter or cleaning it. However, the presence of dirt may also indicate problems with the cylinder-piston system. If it wears out badly, there is no point in repairing the engine; it is easier to buy a new unit.
Start the engine, the car should be in working condition in a couple of minutes, this is enough to warm up the engine. If the engine is not started immediately, but after several revolutions of the crankshaft, then there are hidden defects. Try starting the car at different intervals several times. Every time the car must respond quickly to the turn of the key.

You should be alerted to abnormal exhaust gases. Light blackness is acceptable, however, all other shades of the exhaust indicate probable problems in its subsequent operation.

Also, pay attention to the characteristic tapping sounds. These appear if the engine is deformed, or some of its parts are not securely fastened, or the fastenings are loose.

Please note that at sub-zero temperatures the engine will take longer to warm up. Therefore, it is not recommended to buy a car in winter, since it is not possible to properly check it for proper operation.

Fuel costs are a characteristic that, nowadays, is often at the forefront when choosing a car. Diesel fuel today is cheaper than 92-grade gasoline, and despite this, very soon after purchasing a car with a diesel engine, many car owners experience disappointment. The reason is that most drivers are not accustomed to diesel engines; they prefer gasoline cars. At the same time, in some European countries, for example, France, Spain, cars with diesel engines are very popular, which is confirmed by sales volumes - sometimes more diesel versions are bought than gasoline ones. In our country, there are a number of factors that explain the “cool” attitude towards this type of motor. And yet, those who decide to purchase a diesel engine should know about some of the intricacies of its purchase, operation and maintenance.

Economy is a well-known advantage of diesel engines, which is the main “lure” for buyers. But they also have “disadvantages”, which many, especially fans of comfort and a sporty driving style, soon find themselves not to their liking.

The first thing that gets boring very quickly is the characteristic increased “tractor” sound of a running engine. Although the sound insulation of the interior of foreign cars is not bad, automakers have not yet been able to completely protect those sitting in the cabin from diesel “music”. Then, although not in all cars, increased vibrations begin to irritate. And those who like to “get dirty” will clearly not like the weak acceleration dynamics, especially when it is necessary to accelerate at high speeds.

It is interesting that buyers manage to become familiar with all these shortcomings even when inspecting the car offered for purchase. But “programmed” for efficiency, many do not pay attention to these “nuances”. Only after some time have passed, new car owners begin to join the ranks of those dissatisfied with diesel cars.

The picture is complemented by the fact that diesel is a specific type of engine with an individual character, which determines the characteristics of its operation and requires compliance with certain operating and management rules. Usually they are not known, and if they are known, they are not observed. As a result, the diesel engine, instead of the required 500-600 thousand kilometers before major repairs, takes two or even three times less to maintain. So before you buy a diesel, make sure it suits your temperament and driving style and that you can "meet" its operating and maintenance needs.

Although the car market offers much fewer diesel foreign cars than gasoline ones, if you really want to, you can still find the right option. The control inspection of diesel cars is no different from gasoline cars in many respects - checking the body, chassis, transmission, serviceability of electrical equipment, etc. The difference lies in the engine testing. Two points are important here - checking during a “cold start” and the nature of the “hot” operation. It should, however, be noted that summer is not the best time to purchase a diesel engine. Therefore, if after this article someone has a desire to become the owner of a diesel car, it is better to wait for the onset of a cooler season. The ideal period for testing a diesel engine is winter, when the frost outside is 10-20 degrees. Under such conditions, “diseases” of this type of engine are much easier to identify. The main indicator characterizing the serviceability of a diesel engine is a “cold start”. It is carried out in the following sequence: to increase the fuel supply, the manual “gas” button is pulled out (if a thermal bleed is not installed); turning the ignition key turns on the glow plugs, which is indicated by the glow plug indicator on the instrument panel lighting up - a yellow lamp with a spiral symbol; when the spark plugs have warmed up (this takes about 20-30 seconds), the lamp goes out - this is a signal allowing the engine to start. If, after performing these operations, the engine starts on the first try and without prolonged rotation of the starter, then everything is normal.

A diesel engine does not start in the cold mainly for several reasons: the battery is dead, the glow plugs are faulty, the fuel system uses summer fuel, the cylinders have low compression. The procedure for replacing the battery and glow plugs does not require particularly large expenses (2000 - 3000 rubles). But as for low compression in the cylinders, there is a need for an expensive overhaul of the engine (30,000 - 50,000 rubles). Fuel that has frozen to a gel-like state is not able to pass through the filter, which means it can only be removed from the power system during heating in a warm garage, followed by replacement with winter diesel fuel or the addition of anti-gel additives.

While the diesel engine is cold, its operation is usually accompanied by increased noise and black exhaust. This is a common occurrence for this type of engine, since fuel in cold cylinders does not evaporate well and therefore does not burn completely. As a working diesel engine warms up, the noise decreases and the black exhaust disappears. If the nature of the work does not change and smoke continues to pour out of the chimney, then something is faulty. Blue smoke is a sign of wear of parts of the cylinder-piston group (piston rings, liners, pistons), which requires a major engine overhaul. When the exhaust is black, it means the fuel in the cylinders is not completely burned. This occurs in the following cases: poor-quality fuel atomization due to faulty injectors or their nozzles; supply of excess fuel by a misregulated fuel pump; lack of air in the cylinders with a clogged air filter.

As practice shows, the service life of passenger diesel engines in our operating conditions ranges from 200 to 600 thousand km. Such a significant spread is due to the large dependence of the diesel resource on operating conditions, systematicity and quality of maintenance.

The ability to operate a diesel engine is perhaps the main factor that has the greatest impact on its service life. This type of engine does not forgive the mistakes of the driver, who, for example, is accustomed to revving high-speed gasoline engines to the maximum and forces diesel engines to work in the same mode. Owners of such cars should remember one important rule - diesel does not like high speeds, since this significantly increases the load on the parts of the cylinder-piston group, fuel equipment, and the process of mixture formation and combustion itself does not proceed according to the required “scenario”. Therefore, you need to drive at average speeds or below average, and you should switch to higher gears much earlier than in the case of a gasoline engine. This has long been tested in practice. It is not without reason that at many motor transport enterprises, before “putting” a driver on a diesel engine, he undergoes an internship. If this is not done, the service life of engines in the hands of untrained drivers is reduced by 3-5 times, and sometimes more.

To reduce the impact of mechanical impurities and water contained in our diesel fuel on the very sensitive fuel equipment of diesel engines, it is advisable to equip the power system with a separator filter, preferably heated. This will extend the life of expensive fuel pumps and injectors and protect yourself from winter problems caused by increased fuel viscosity. If it is not possible to install additional filters, it is better to first let the fuel settle in some kind of settling tank. By the way, you can pour it into the tank without stirring it in the sump only after two or three days.
You should also know that it is undesirable to start a diesel engine from a pusher or in tow, since due to high compression in the cylinders, there is a high probability of a break in the timing belt (if the drive is belt driven). We have already written about the consequences this can lead to.

An important aspect that affects the life of a diesel engine is the timeliness of maintenance and the quality of the materials and spare parts used. Under no circumstances should you fill imported diesel engines with the first available oil, including the Kamaz M10/G2K oil that was popular in Soviet times. You need to pour only what the manufacturer recommends or the best quality, for example, instead of oil of the SS and even CE quality category according to the API, CD class oil, which is intended for highly accelerated diesel engines with high pressure supercharging, operating in difficult conditions on high-sulfur fuel.

Turbodiesels are especially demanding on the quality of oil. Under conditions of high temperatures and turbocharger shaft rotation speeds, only high-quality special oils for turbodiesel engines can maintain lubricating properties. Ignoring this requirement leads to the fact that, under such harsh conditions, the oil film on rubbing surfaces obtained by using low-grade oil is very quickly destroyed. This causes dry friction and, accordingly, increased wear of the shaft, turbine bearings and rapid breakdown of the turbine as a whole.

For the same reasons, diesel engine maintenance must be carried out in due time. Although, when using our diesel fuel with a high sulfur content, which promotes accelerated oxidation of motor oil, it is better to reduce the replacement interval by 20-30%. For example, if, according to the operating manual for a particular car, the replacement frequency is 10 thousand km, this should be done after 7-8 thousand km.

An important factor for the “health” of a diesel engine is oil filters. The filter element of diesel filters has very small cells that trap particles that a gasoline engine filter easily passes into the lubrication system. Therefore, you need to buy only high-quality oil filters for diesel engines - original or well-known companies (Bosch, Champion, Delphi, etc.). Counterfeits and products of unknown origin may use filter paper from a gasoline filter.

If “mineral water” or “semi-synthetic” is poured into the engine, it is advisable to flush the lubrication system every 20 - 40 thousand km (depending on the quality of the oil - domestic or foreign). In the case of “synthetics” with its excellent cleaning properties, you can flush the lubrication system less often.

Maintenance costs for diesel vehicles are lower than for gasoline vehicles. Savings are achieved due to the absence of spark plugs, which are changed more often than glow plugs, in addition, there are no complex electronics that control the operation of the power system (we are talking about diesel engines produced before the mid-90s). So think, YOU need this.

Buying a used car is a fairly responsible procedure, as it involves a large number of legal and technical checks. As for technology, that is, analysis of the condition of the vehicle itself, when buying a used car, maximum attention should be paid to the most expensive elements: the body, engine, transmission, individual components of the chassis and steering.

If the condition of the body can be assessed visually, and the serviceability of the chassis can be easily checked on a lift and tested on the road, then the issue with the engine is not so easy to resolve. As a rule, the seller will not allow you to open the engine for diagnostics. Similar difficulties arise when it is necessary to check the removed engine at .

In this article we intend to talk about how to check the condition of the engine when buying a car with gasoline, as well as what methods help to check when buying a car.

Read in this article

Checking a used engine before purchasing

Let's start with the fact that a lot about the condition of the engine can be learned by visually inspecting the engine itself and the engine compartment. First of all, you should remember that an apparently clean engine that starts and runs does not mean that the engine is fully functional and in good condition.

Experienced mechanics at service stations are well aware of this, and car resellers and less than honest sellers are also well aware of this. For this reason, when assessing the condition of a used car, you need to clearly know what to look for.

So, let's figure out how to check the engine when purchasing. First of all, even if you don't have much experience, you don't necessarily need to tell the car salesperson. Try to refrain from any unnecessary comments, while following step by step the instructions that we will discuss below.

Before you begin your engine inspection, start with simple questions regarding vehicle and engine repairs and maintenance. Ask what was done on the engine and when, at what mileage was the last time, when was it done, antifreeze, spark plugs, etc.
Also inquire about the type and brand of oil filled (for example, 5W30 or 10W40) and other technical fluids. At the same time, observe the clarity and transparency of the answers and the owner’s reaction.

This approach will immediately allow you to identify either a reseller who does not know the history of the car, or a careless owner who did not pay proper and timely attention to the car.

Visual inspection of the motor

Next, you can proceed to inspecting the engine. If the seller prohibits or deliberately makes it difficult to access certain external elements under the hood, then it is better to immediately refuse to purchase such a car. If no problems arise, you can continue.

As we already said, the first thing you need to pay attention to is traces of engine oil. Oil drips or traces of antifreeze will indicate leaks through gaskets, seals and other seals. In some cases, such problems can then be corrected without major financial investment, while in others, oil can be squeezed out as a result of serious engine failures.

It turns out that a worn gasket or oil seal may be leaking, which is not so difficult to change. However, in some cases, similar leaks can occur for other reasons. For example, when the engine was overheated, it may then “lead”, that is, the geometry of the mating plane is disrupted. As a result, replacing the gasket will no longer solve the problem.

Let us add that even if nothing serious happened to the engine, a dirty internal combustion engine with smudges will indicate that the owner, for some reason, does not pay due attention to the condition of the vehicle, carelessly operates the car, etc. This suggests that the regulations for maintenance, oil changes and consumables could be systematically violated, which is very bad for.

in order to give the car a general presentation;
to hide oil and technical fluids;

Unfortunately, the second case is much more common, since a working engine is rarely washed before sale. Moreover, the sellers specifically draw the buyer’s attention to the fact that the engine is dusty and the engine was not specially washed, that is, it is clearly visible that there are no leaks.

Either way, the discovery of leaks is a cause for concern and/or bargaining. A clean motor should also be cause for concern, which will require a more thorough check. The best option is an engine that is covered with a small layer of old dust, but does not have any leaks.

Checking the condition of oil and antifreeze

If you don’t know how to check a diesel engine when purchasing or you are interested in checking a gasoline unit, then you should start by assessing the condition of the technical working fluids inside the internal combustion engine. We are talking about engine oil and coolant.

Let's start with the oil. The first step is to unscrew the oil filler cap. Ideally, the lid itself should have no traces of obvious oiling on the outside, and the inside surface should also not be dirty, with traces of oil foam, etc. The last statement is also true in relation to the walls of the neck.
Next, you can take out the oil dipstick and assess the condition of the oil. If it is fresh, transparent, and free of foreign impurities and foam, then it will be difficult to quickly determine anything. Black oil indicates that either the lubricant has not been changed for a long time, or as a result of general contamination of the internal combustion engine and the presence of problems.

What should be especially alarming is that the oil in the engine can foam, that is, it forms. In this case, it becomes obvious that liquid is entering from the cooling system. Note that in such a case, either immediately negotiate with the seller the cost of a similar contract motor, or stop further inspection.

As for checking the engine using the cooling system, the task is to determine the breakthrough of gases and their entry into the specified system, as well as to identify the possible appearance of traces of oil in the coolant. For diagnostics, just open the expansion tank cap. If traces of oil are visible and the coolant is bubbling in the tank while the engine is running, then the problem is obvious.

In some cases, the culprit may be a broken one, while in others one should not exclude the possibility of hidden ones.

Diagnostics of engine condition using spark plugs

Checking spark plugs can identify a number of potential engine and system problems.

Attention should be paid to such things as:

oiling;
black, red or white soot;
traces of unburned fuel;

The above and other signs are a clear indicator of certain problems. It is worth considering, since checking the engine by the color of soot and the condition of the spark plugs is an effective method only if certain conditions are met.

Extraneous sounds and engine vibration

Assessing engine performance at the initial stage involves identifying extraneous sounds, tripping, misfires and mixture ignition, as well as other failures in the operation of the internal combustion engine.

After the engine has been started, you need to listen to its operation, and also look at the level of shaking and vibration. If possible, you can use a stethoscope, which will allow you to listen to hidden defects and localize suspicious noises.

Let us immediately note that knocking sounds of different tones and frequencies, as well as uneven operation, indicate the presence of problems. If a gasoline engine operates like a diesel engine, dips occur when you press the gas, the unit shakes violently, etc., then malfunctions are obvious.

Both various systems (ignition, power supply) and individual components inside the internal combustion engine can fail. The crankshaft, pistons, hydraulic compensators or valves, connecting rods, etc. may be knocking. Shaking and vibrations can be a consequence and a sign of breakdowns, but the possibility of problems with the engine mounts should also not be ruled out.

Analysis of the color of exhaust gases when checking the engine

The color and intensity of the exhaust, as well as the composition of the exhaust gases, in many cases clearly indicate the presence or absence of problems with the engine and its systems.

Let's start with the fact that on a properly warmed injection engine in the warm season, practically no smoke is visible. There is also no exhaust smell. In the case of a carburetor, you can sometimes observe light grayish-white smoke, the smell is clearly present.

So, if the engine runs smoothly, does not smoke, does not knock or vibrate at idle, and also responds quickly and clearly to pressing the gas pedal, then you can take a test drive.

Let’s make a reservation right away: a short drive will not be enough. It is important to evaluate the operation of the unit in different modes, as well as warm up the engine to operating temperatures. For this reason, you should count on a distance of at least 10-15 km.

To solve the problem, you should offer the car seller reasonable compensation for spent fuel and time costs. Next, you need to ask the owner, who will be in the car with you, not to make noise. You will also need to turn off the speaker system to be able to listen to all extraneous sounds.

First of all, take a look at the dashboard, not . At the same time, evaluate the sound of the engine when accelerating, during, during sharp acceleration, etc. Also, while driving, you can listen to the engine alternately with the driver and/or passenger window open and closed.

While driving, pay attention to jerks, vibrations, knocks and whistles. If nothing of the kind is detected, then at the end of the trip, immediately open the hood and evaluate the external condition of the heated internal combustion engine. The presence of fresh smudges on a clean engine will indicate problems that the seller wanted to hide by first washing the engine compartment

Check the oil level and condition again, also allow the unit to cool a little and look into the expansion tank, assess the condition and type of coolant. There should be no smoke coming out of the tank, and there should be no oil stains on the surface of the antifreeze.
If the situation allows, you can re-unscrew the spark plugs and re-evaluate their condition. In some cases, it is possible to reach an agreement with the owner and even produce it (if the buyer has a compression gauge).

As you can see, a superficial inspection and check of the engine before purchase allows you to identify a large number of hidden defects with the right approach. If you are not confident in your abilities, then the right decision would be to order a comprehensive diagnosis of the power unit and the entire vehicle at a service station. Specialists will carry out a repair, point out possible problems and immediately announce the approximate cost of repairs.

In the future, the information received can be used as a valid reason for refusing to purchase or reasoned bargaining. Finally, let’s add that for quick diagnostics of cars with it is useful to have a compact diagnostic tool. The device allows you to quickly scan the system for errors, as well as evaluate the operation of engine systems in real time.

So, you have decided to buy a car with a diesel engine. For a post-Soviet person who had not previously worked as an Ikarus or KAMAZ driver, the word “diesel” always evoked a kind of sacred awe - this creation of the human mind seemed to be a very complex, dark and incomprehensible subject. Therefore, a daredevil who has decided to take such a desperate step - to radically change his usual gasoline life and buy a car, not only is it, in the vast majority of cases, imported and not new, but there are many questions about what to do with this car before and after the purchase.

Do you want to buy a diesel car?

What should you pay attention to when purchasing? To begin with, everything is the same as when buying any car (general condition, mileage, areas of corrosion, and so on). If you are buying from a stranger, do not notify him in advance of your plans to check something - take him by surprise with the following check:

How does a cold engine start (in the morning, for example).
If you have to turn the starter even a little more, this is already an alarming sign (wear of the rings, piston). It is advisable that the engine be completely cold when starting. A working diesel engine should start with half a turn. A cold diesel engine is quite noisy. Warmed up - much quieter. Try starting a hot engine; on some models, the heating does not turn on and starting occurs due to compression.
My car has a similar picture. When cold, it starts with half a turn, and when hot, you have to make from 3 to 10 attempts. After disassembly, the diagnosis was confirmed - wear of the rings. However, this may not happen on all cars: some have a sensor - if the temperature on a warm engine is not sufficient to warm up the combustion chamber, then the glow plugs turn on. It's another matter when this sensor does not work.
and the condition of the fuel equipment.
When you press the accelerator on a warm engine, check to see if smoke is coming out of the exhaust pipe. If the smoke is dark, then most likely the oil scraper rings are worn out, or the injectors are out of order, in general - nothing good. If there is white smoke, water is getting into the fuel somewhere.
A simple method: put a piece of paper under the exhaust and see if there is soot, then most likely it is burning oil (oil soot) or incomplete combustion of the fuel. If there is a turbine, then black smoke may continue until it is turned on. While driving, there may be black smoke when over-gasping, but it is short-lived and not thick. The smoke may also be due to a clogged air filter - try running the engine without it.
The sound of the engine.
If the sound is uneven, tapping, the engine may have incorrect valve clearance, or something is wrong with the valves themselves or the piston. It is possible that everything can be corrected with basic adjustments. By the sound of the engine you can also assess the condition of the fuel equipment: - “hard” sound, black smoke at high speeds - early injection angle; - interruptions and gray smoke at idle and black smoke and interruptions at high - late injection angle; - uneven operation at idle and black smoke - a non-working injector, you can definitely determine this by turning it off. The pump should not rattle.
The engine should run smoothly, “rumble” solidly, in a word, “diesel-like.” Try to hear (although it is difficult on an unfamiliar diesel engine) extraneous noises at different speeds, when they are set and reset, how the piston and crankshaft work.
Open the oil cap.
If oil splashes out of the oil filler neck, this is an indication that there is a gas breakthrough somewhere (or maybe the guides are simply broken). This thing, although unpleasant, is not fatal. There can be many reasons - both serious and funny.
At the same time, you can seriously bring down the price - by shaking your head and speaking in this way: “Yes, man, your engine is dead! A piston, covered in one place - the oil is driven under the cap, and the rest...” Let him try to prove Life will not prove that this is not the case until you measure the compression.
General appearance of the engine compartment.
Determine whether the injector nuts, the cylinder block are loose, or traces of white or red sealant (the Japanese use only black) - this means that the engine has been tampered with. All accessory mounting bolts must be in place. Only our service can easily not install a hard-to-reach bolt.
The condition of the liners can be assessed by warming up the car, turning off the ignition and immediately turning on the ignition: the oil pressure light should light up in a couple of seconds. If earlier, either the oil is liquid or the liners are not in order. The second one is more likely.

More complex procedures:

If you have completed all of the above steps and after that you are not disappointed in life, then this is already good. It's even better if you still want to buy the same car. Then, if you have the opportunity, it is strongly recommended to perform the following steps, which speak volumes (at the station or, if possible, better with friends).

A. Measure the compression. It is measured correctly like this:

Unscrew all injectors.
The starter pumps the cylinders a couple of times to prevent oil or fuel from getting into the cylinders, which can affect the compression value.
Screw the compression gauge into place of the injector and use the starter to crank the engine several times until the arrow stops.
Everything is repeated on other cylinders. The compression should, firstly, not be lower than 25, although it may be different for each volume. The smaller the spread of values across cylinders, the better. The standard for a new car is 0.5, no more. For an old car, this is, of course, impossible, but if there are values like 18-25-30-22 with a standard of 25, this indicates the possibility of a quick overhaul.

If the compression is low, it's not the end of the world. First, you can find out what the cause is - and, accordingly, how much the repair will cost. Low compression occurs for two reasons:

Piston wear (gases break through the gaps between the liner and the piston)
Wear of valves (gas breakthrough through guides, seals).

To check, take a little oil into a syringe, inject it into the nozzle hole, screw in the compression gauge again and measure the compression again. The idea is simple: if the rings are worn, oil flows into the gaps and prevents gases from escaping, and compression should increase. If it remains the same, then the valves are worn out, which is both cheaper and easier to repair. Yes, and don’t tell the seller about your intention in advance - otherwise they’ll pour in some nasty stuff to increase the compression, and then you won’t have any problems.

B. Check the injectors. A normal injector, when fuel is supplied to it under pressure, should emit a very characteristic “buk-buk-buk” and spray “into the fog”: All kinds of rain and trickles are not welcome. Increased black smoke may still occur if the cutoff in the injectors does not work. Sprayers need to be removed and inspected. Spraying in the form of drops and streams is strictly not recommended - you can burn the pistons or head, depending on where it sprays. Determine the condition of the fuel supply and return hoses. If the seal is broken, there will be problems with starting.

B. Glow plugs/combustion chamber heating. The activation of the heating relay is checked by ear and by the lights on the dashboard. By the speed at which the relay turns off, you can determine which spark plugs are not working. Using a voltmeter, you can first make sure that 12V is supplied to the spark plugs. After starting or after 5-10 seconds it drops to 6V, and after the engine warms up - to 0. But it varies on different machines. If candles designed for 8 seconds. After warming up, put it on a car with a relay that outputs 13 seconds, there is a high probability that they will burn out. And the speed at which the relay turns off does not mean anything at all - it gave out 10 seconds. and turned off, and the spark plugs may be faulty. Moreover, we cannot determine anything by hearing.

D. Oil color. Oil color is black, without foreign inclusions. A quick, about 500 kilometers, darkening of the oil after changing it (not due to a mixture with the old one) is an indirect sign of ring wear. If the oil has a characteristic silver-gray tint, then there is a fairly high probability that the engine has been “treated” with some kind of molybdenum additive.

D. Cooling system. There should be no bubbles in the cooling system; this is checked at medium and high speeds with the engine warming up. If there are bubbles, the gasket has burned out, or the cylinder head has moved. Estimate the response time of the thermostat; the engine at idle may not warm up above 40-60 degrees, but after 5 minutes of driving, the needle on the scale showing the coolant temperature should show operating temperature. The iron pipes of the cooling system near the block should not have rust or a characteristic red coating, like the exhaust manifold - a suspicion that it was overheated.

E. Measure the pressure of crankcase gases. High pressure, again, indicates wear on the piston or valves.

Immediately after purchase

If you were not afraid of all of the above, and still bought a car, then immediately perform the following magical actions:

Change the timing belt immediately, no matter what the seller tells you. Take a branded belt, don’t buy a cheap one. If, God forbid, it breaks, at least the valves have a cover. Have your belt changed by a professional. I've seen an Audi with a cylinder head torn off and trashed only because the owner was stingy to buy a good belt.
After purchase, monitor the oil level. If the level decreases without visible oil leaks, this is a clear sign of worn oil scraper rings.
Change the oil and fuel filters regardless of when the seller says he changed them. Especially if you bought a car on the eve of winter.
Naturally, when performing the above actions, it is advisable to change the oil. I recommend: Shell Helix Ultra Plus 5W-40 synthetic. It started at -33° even with very poor compression. P/synthetic Chevron Diesel SAE 10W40 API CF/SE plus REDEX molybdenum additive. By the way, it is best to take oil with API CF or CE classification. CF is the best. SS and CD are designed for diesel engines operating at medium loads, which is not very suitable for our fuel. Abroad, it is just right for old diesel engines, but here we must consider all conditions to be the most difficult and unfavorable, and take oil accordingly.
In addition, study the numbers on the battery that you received with the car. A diesel engine, especially if it does not have very good compression, needs a good battery (return current: the higher the better), thinner oil and a working heating system to start the engine. For example, I have 100Ah/450A at - 18.
Also, as a first step after purchase, we recommend carrying out diagnostics at a service station (costs from 30 to 60 dollars), which can tell you a lot about the car. Although the stations are also different and can say different things. So don't be too scared. It is best to ask the opinion of several specialists (they, as a rule, are very contradictory).

Some time has passed since purchase

So, you are driving your newly purchased diesel car, and, we hope, you are getting a lot of pleasure from it. But somewhere in the depths of my soul a thought torments me: “Now it’s good, but some time will pass and...” What to do to prevent this “and...” from happening? It’s difficult to give advice for all occasions, but some general advice can be given:

Avoid “cheap” options from nowhere (tractor, ship, locomotive diesel fuel). It's very hard to guess here. We once took luxurious locomotive diesel fuel, but our friend, or rather his car, was very damaged by the ship's diesel fuel. Only refuel if someone already drives this diesel fuel and is happy with it.
Change the fuel filter more often than required in the service book. Given the quality of our fuel, this is a decisive factor for the normal operation of the machine, especially in the cold season. You can install an additional fuel filter.
Don't skimp on oil, especially for winter. For our winters, mineral water 10W30 is best, synthetic water 10W40, synthetic 5W40, other SAE markings - look at the catalog for temperature limits.
Fuel and oil additives.

We do not recommend getting carried away with adding additives, especially cleaning ones, and especially those of unknown origin. The cleaning additive has the ability to wash out all the dirt and muck from the tank and pipelines and drive it all into the fuel pump; the filter cannot retain everything. The result is high costs for repairing the pump and/or motor.

You can stock up on anti-gel for the winter. I use Kleen-Flo (Canada) and REDEX (GB). The antigel should be added to the fuel according to the instructions until the diesel fuel thickens. After that it will no longer work. Although diesel fuel from new, decent gas stations at more or less low temperatures (about -10-15) should not gel too much.

I highly recommend the molybdenum oil additive from REDEX. Firstly, the molybdenum compounds contained in it enter into molecular interaction with the rubbing surfaces in the engine and create a thin protective layer that reduces wear and friction. Secondly, these compounds heal microcracks and minor surface damage. It lasts for 75,000 kilometers, i.e. The protective layer is not washed off when . In practice, this is expressed in a sharp decrease in noise during engine operation and fuel savings. This is not an advertisement, I tried it myself and am very pleased.

You can also add some so-called conditioners, i.e. additives designed to improve fuel performance. Manufacturers attribute to them a magical effect of binding water, increasing the cetane number, reducing consumption, etc. Again, I gradually add REDEX conditioner. It doesn't seem to do any harm. Try to buy all fuel additives from the same company. They all seem to be compatible, but it’s better not to risk mixing additives from different companies.

Do not experiment with additives to increase compression - when you need to replace the rings - “you can’t revive a dead man with poultices,” and they can do a lot of harm.