Here's why:
* The rocker cover houses the valve train and is part of the top of the engine. Exhaust gases belong in the exhaust system, not escaping here.
* Head gasket failure: This is the most likely culprit. The head gasket seals the combustion chamber from the engine's cooling system and oil passages. If it fails, combustion pressure can force gases into the oil passages, leading to them escaping through the valve cover. You might also see milky oil (oil mixed with coolant) or coolant loss.
* Cracked cylinder head: A crack in the cylinder head can also allow combustion gases to escape into the engine's oil passages, creating the same symptoms.
This is not a minor issue. Continuing to drive the car with this problem will cause significant and potentially catastrophic engine damage, leading to a very costly repair or engine replacement. The engine needs immediate attention; driving it risks severe internal damage from overheating and lack of lubrication. You should have a mechanic diagnose and repair the problem as soon as possible.
