Hello, I have E60 520i (M54B22), 2004, gasoline, 270,000 km. Ever since I bought the car it had a problem. When I accelerate over 3500rpm some kind of smell comes into the cabin. If I drive softly it doesn't appear.

Previous owner had changed the valve cover as it has been leaking and mechanic told me that the smell is probably from old oil that was leaking at the valve cover and that it should burn off. It has been few months and the smell still comes when accelerating.

Currently it doesn't leak oil at the valve cover or anywhere on the side where the exhaust system is. By logic the smell would come from oil dripping somwhere and hitting hot exhaust.

Any ideas what should I check next. I am not 100% sure I smell burned oil it could be other liquids. I have been losing a bit of coolant but not much at all and I have checked for leaking coolant (I dont have the tools to check for leaks to create pressure) but when the car is running I can't see any drips of coolant.

Any suggestions would be appreciated. Thank you!