Mercedes-Benz W202 head gasket: symptoms and confirmation
Mercedes-Benz W202 uses coolant but no leak is visible – has the head gasket gone?
It is a common cause. Other symptoms are running on fewer cylinders after a cold start, white smoke, grey engine oil, and oil or mayonnaise-like paste in the expansion tank. The leak is often at the rear of the engine, for example under the exhaust manifold.
Is paste inside the oil filler cap a sign of a head gasket fault?
Not necessarily. Short trips produce condensation water, which shows up under the cap as a mustard-like or butter-like paste. If there is no liquid in the oil and no coolant is disappearing, it is usually not a head gasket problem.
How is the head gasket confirmed before repair?
Start with a pressure test of the cooling system, since the leak often shows only under pressure. Also check under the oil filler cap and the colour of the oil. If coolant has got into the oil, do not drive, because glycol quickly damages the connecting rod bearings.
Can oil end up in the coolant from somewhere other than the head gasket?
Yes. The oil cooler leaks oil into the coolant, and the leak continues even if the head has already been resealed. Check the cooler and its hoses before resealing the head unnecessarily.