Attention! If you have the slightest doubt about the results of self-diagnosis, get the towline. Serious repairs to a damaged engine will cost more than the services of a towing vehicle.
Knock of main bearings - very dangerous; stop the engine immediately, you will have to go to a car service or garage in tow. Low tone knock. It is audible in the lower part of the crankcase, noticeably increases under load and with an increase in speed. Often its appearance is accompanied by a drop in oil pressure (The oil pressure warning light is almost constantly on).
Knocking rod bearings - very dangerous; stop the engine immediately, you will have to go to a car service or garage in tow. The sound is rhythmic, ringing, metallic, medium tone. Significantly increases with increasing load and completely disappears when the spark plug is turned off.
Knock of piston pins - dangerous; without loading the engine, you can drive to a car service or garage on your own. Rhythmic, high tone with a sharp metallic tinge, audible in all engine operating modes and intensifies with increasing engine load. Completely disappears when the spark plug is turned off.
The sound of worn pistons and cylinders - not dangerous; without heavily loading the engine, you can drive to a car service or garage on your own. A sound reminiscent of the clatter of pottery. It is especially well heard on a cold engine, as it warms up it decreases or disappears.
Valve knock - not dangerous; you can drive to a car service or garage on your own. A metallic thump against the background of a general muffled noise. It is well audible at low and medium speeds of the crankshaft from the side of the cylinder head above the valve locations.
detonation knocks - dangerous; however, avoiding a heavy engine load, you can drive to a car service or garage on your own. Voiced metallic knocks that occur, as a rule, during acceleration of the car. The reason is a malfunction of the knock sensor, the use of low-octane fuel, engine overload with too early upshift, significant carbon formation in the combustion chambers. It is necessary to choose the right gear depending on the driving conditions, refuel with gasoline with an octane rating recommended by the car manufacturer, check the knock sensor, apply a special fuel additive to remove carbon deposits on the valves and in the combustion chambers.