I've read that too much engine oil can damage your engine, however I've also seen mechanics suggest you should just let excess engine oil burn off with driving so it's 'nothing to worry about'. These seem a contradiction of statements.
When do you know whether to let it burn off and whether to drain it? I'm assuming they mean if it's a bit over it's not a problem. If so would a few mm or 1l be too much or too less etc.
The problem is, if your engine is running correctly, it won't burn it off. While engines will use a little bit of oil, most of that oil is replaced by unburnt hydrocarbons introduced through blowby. Due to this, oil levels most often stay right about where they should be throughout the life expectancy of oil. If you have too much oil in it, it won't go down, so remove the excess.
Engineers decide how much oil a given engine requires. If you add too much it can cause engine damage. One of the issues with an overfull crankcase is the crankshaft may dip into the oil in the oil pan. This can result in the oil being whipped into a foam. The foam by nature contains air bubbles. The air bubbles are compressible meaning you could develop a low oil pressure condition. You could also get to the point where the engine could hydro-lock. meaning the combustion chamber gets full of oil preventing the piston from moving.
