What will happen if the oil level is too full?

Hello, Too much motor oil will, at least, cause the engine to run extremely inefficiently, and, at worst, cause a spun crankshaft bearing leading to engine seizure. Also, expect oil leaks, the check engine light, stalling or harsh idle, and very poor acceleration. Now, if the engine is just over-filled, as in a quart or less, there is only a real risk of creating oil leaks, but performance may be slightly inhibited.