What can go wrong if you put in too much engine oil?
Can you mix engine oils of different ratings (10w40 and 15w40)?
I don't recommend mixing oils of vastly different viscosities, unless its an emergency. I.e. your 400km out in the boonies, and the hicktown service station only carries 10w30, and for some reason you're a liter low. Go ahead and use the 10w30 so you can get home...
Otherwise, there's no reason to mix oils. Its only a few bucks to fill your crankcase properly.
dont overfill your crankcase. raises the pressure too much and is bad for your engine.
One more time eh?
too much oil in your engine will bet churned around by parts of the motor that usually are not immersed in oil, the crankshaft and connecting rod are the major culprits here. (preasure lubed, not splash) all this whipped up oil usually gets pumped into the air box and can soak into the air filter and generally create a bit of a mess. Save yourself some hassle and drain out the excess.