How to check a diesel engine when buying a car without special tools

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.

Deductive method

An example of carrying out indirect measurements on a diesel engine, bypassing risky measures, is a comparison of compression in cylinders using a current sensor. From the outside, the process looks like electrical diagnostics, but in fact it is an effective check of the mechanical part of the engine.

The most difficult task is to identify floating faults that leave almost no evidence and reveal themselves only in certain engine operating modes. Only an experienced diagnostician-detective, armed with a good scanner, can handle it. He will be lucky if, over several trips, comparing the key operating parameters of the main engine systems, he can catch the culprit. But often the diagnostician has to use workarounds in order to narrow down the circle of suspects.

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:
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.

Standard scheme

Diagnostics of other diesel systems is simpler, but you still can’t do it without special equipment. Before removing the glow plugs for inspection, measure their voltage and resistance. The optimal test is to connect a current sensor used to measure compression. Usually the candles are controlled by a separate unit. The sensor is hung on its supply wire and the total current consumption is recorded: by its significant drop, you can immediately determine that one or two spark plugs are not working. Next, they move on to checking specific candles.

Diesel engines have a vacuum system that is usually more complex than gasoline engines, so to check the tightness of its lines, auxiliary equipment is often used - a smoke machine. The leaking smoke will definitely indicate a leaky place. This device is also used to check the tightness of the intake tract of the supercharging system. But its control part (if it is of the vacuum type) is tested in a combined way. The readings of a vacuum gauge connected to various points in the system are compared with data received from the scanner on the control effect on the solenoid and boost pressure.

A smoke machine is a valuable assistant for checking the tightness of the intake tract and vacuum system of a diesel engine.

This is what the process of checking the so-called return looks like. It is clearly visible that the third nozzle sends much more diesel fuel to the drain than all the others. However, this is not a reason to immediately sentence her - additional tests are needed.

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.

Why such delicacy?

The problem is that a modern diesel engine is a complex power unit design, where the failure of one component almost always entails a whole series of subsequent damage.

For example, a malfunction in the power system. The very elimination of such a malfunction entails additional financial costs. However, it may turn out that as a result of such a breakdown the turbocharger, particulate filter or exhaust gas recirculation valve was damaged. Unfortunately, we must honestly say that modern diesel engines have many advantages, but they allow the first owner to enjoy their advantages. When such cars enter the secondary market (usually after 150-200 thousand km), a phase of increased engine accidents begins.

When buying such a car, you should be aware that several important components, such as: a turbocharger, an injection system, a recirculation system, a dual-mass flywheel or a particulate filter, can fail at any time, and repairing each of these elements costs several thousand hryvnia! Here are a few basic things to pay attention to.

Used diesel: how to check before buying

More recently, automakers amazed the world with the release of diesel versions of sports cars. The Audi TT, Škoda Octavia RS or Peugeot 406 Coupe seemed to encroach on the core values of sportiness: a manual gearbox, rear-wheel drive and a petrol engine. Probably, it couldn’t have been any other way - the opportunity to drive in style and economically seemed too tempting.

Diesel "Audi TT"

In the last decade, diesel models have become popular among most classes of cars, from small city cars to large all-terrain vehicles, as well as the already mentioned sports cars. People choose used diesel models even despite the slightly higher operating costs - everything is overshadowed by low fuel consumption.

Below we will give some tips on how to check a diesel car yourself when buying it. By following the steps already mentioned, you will reduce the possibility of purchasing a bad vehicle:

Unscrew the oil filler cap, but do not remove it. Ask the owner of the car or the person accompanying you to hold down the accelerator pedal of the car for a while. Check the cover: if the engine pulls it in, everything is fine, if it pushes it out, the engine compression is probably too low.
Inspect the lid itself - there should be no sediment of a pasty consistency on it. If they still exist, this may indicate an overheated engine or an untimely oil change.
Until the owner of the car or your friend gets out of the car, ask him to press the accelerator pedal harder. Keep an eye on the exhaust pipe: if what you see resembles a slight black smoke, it’s okay, but if thick bluish smoke starts pouring out, you may have to change the turbine in the near future.
Select the so-called oil dipstick and pay attention to whether steam or smoke rises from the hole. They shouldn't exist. True, this advice does not apply to new cars.
Do not rush to turn off the car engine. Let it warm up to operating temperature. Then turn it off, wait 5 minutes and try again. The motor should start running instantly. If this is not the case (i.e., the engine starts working only after 2-3 rotations of the crankshaft), you will probably have to visit a car service center in the near future.
Avoid the 2.5 TDI V-engine, which was installed in Volkswagen, Audi, Škoda cars. Due to its defective design, it requires more maintenance and cannot always respond with its durability.
Keep in mind that even in a new car, the engine may be unclean and, experienced people say, there is nothing to worry about. The main thing is that there are no traces of oil leaks on it, indicating more serious problems. Therefore, carefully examine a ten-year-old car whose engine is clean. It was probably not in vain that they washed it. And it’s better to be accused of being morbidly suspicious than to buy a bad car.

Good luck with your choice!

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