overfilling the crankcase results in the engine oil being whipped by the connecting rods and the crankshaft creating foam of the engine oil. foam oil does not lubricate moving parts as well as liquid engine oil. the foam oil gets carried into the intake through the pcv valve and it serves as fuel inside the combustion chambers as mentioned by ibaloi. this unintentional temporary fuel supply can not be controlled and the runaway engine has a potential to self destruct because of uncontrolled engine speed. similar to claims about engines running wild, a novice driver panics and causes an accident causing harm to himself and/or other motorists.