Buying a diesel car for an uninitiated person is a difficult, dark and incomprehensible business. Therefore, you should know how to choose the right diesel car in order to avoid the disappointment of the purchase.
It is necessary
Compression level meter, crankcase pressure meter and other equipment for engine diagnostics
Instructions
Step 1
First, you should check how the engine starts in a cold state. It is best to do this in the morning to keep the engine completely cold. A serviceable diesel engine will start from half a turn. If it does not start immediately, this is a bad sign (wear of the piston or rings). Cold will make a noticeable noise, warmed up - much quieter. If you start a hot engine, on many models the heating will not turn on, and the start will occur due to compression.
When you press the gas pedal on a warm engine, you should check if smoke is coming out of the exhaust pipe. If the smoke is dark, it means that the oil scraper rings are worn or the nozzles are malfunctioning. White smoke means water has entered the fuel. A commonly used method: a white handkerchief or piece of paper is placed under the exhaust. The presence of soot on paper or cloth indicates increased oil consumption or incomplete combustion of the fuel. On a turbodiesel, black smoke is allowed until the turbine is turned on, as well as during re-gasification. But it should be short-lived and not thick. It is worth trying running the engine without an air filter. A clogged filter may be the cause of increased smoke.
Step 2
An uneven, tapping sound of the engine operation indicates improper valve adjustment, and possibly problems with the valves themselves or the piston. A "hard" sound combined with black smoke at high revs means an early injection angle. Intermittent and gray smoke at idle, combined with intermittent and black smoke at high - late injection angle. Irregular operation of the diesel engine at idle speed in combination with black smoke reveals an inoperative injector. To test this, disable it. The engine will run smoothly.
After opening the oil cap, check that there are no splashes of oil from the oil filler neck. Their presence is an indicator of gas breakthrough. There can be many reasons for this.
The general view of the engine compartment should be assessed. If the nuts of the injectors and the cylinder block do not have dents, if there are traces of white or red sealant (black for Japanese cars), then the engine was not opened. You also need to check the presence of the bolts that secure all accessories. The condition of the liners is checked as follows: warm up the car, turn off and immediately turn on the ignition. The oil pressure indicator should light up after 2-3 seconds. If earlier - the earbuds should be changed.
Step 3
Compression
Compression should be measured at a station or equipped garage. Compression must be at least 25. However, this value may be different for each engine size. The range of values should not exceed 0.5 for a new car and 1-2 for an old one. A strong spread indicates an imminent overhaul. Low compression can be due to piston wear or valve wear. Valve wear is cheaper and easier to repair.
Step 4
Injectors
During operation, the nozzle should make a characteristic sound and spray fuel into a dusty state. Spraying in the form of drops and jets is absolutely contraindicated for the engine. Together with the injectors, the tightness of the fuel supply and return hoses should be assessed.
Step 5
Butter
The color of the oil should be black, without impurities. The silvery gray shade of the oil indicates the recent use of molybdenum additives.
Step 6
Cooling system
Check the absence of bubbles on a warm engine at medium and high speeds. There should be no rust or red deposits on the metal pipes of the system (a sign that the engine has overheated).
Step 7
The last step is to measure the pressure of the crankcase gases. A high value of this indicator can only be due to wear of the piston or valves.
