There IS such a thing as too much oil.
I bought a new Ford F-150 pick up truck. When I got it home, I checked the dip stick and it was one inch over the full mark. I took it back to the dealer and talked to the service manager. He told me it's OK to drive. My owner's manual says "do not overfill." Is it OK to drive?
RAY: No, Walter, it's NOT OK to drive. When there's too much oil in the crankcase, the spinning crankshaft can come in contact with the oil and whip it up into a foam.
TOM: Foam's great if you're shaving or making 10W-30-meringue pie, but it's lousy if you're trying to pump oil around the engine.
RAY: It sounds like the service manager just didn't feel like helping you. Maybe he had somewhere else to go. Did you happen to notice whether he was polishing any golf clubs while he was talking to you?
TOM: The truth is it's a bit of a pain in the neck to take a quart of oil out of an engine. You have to drain out all the oil, and then put most of it back in again. But they HAVE to do it for you, Walter. Go back in and insist. And take your own 9 iron with you so you can make your case more persuasively this time.