You have that backward. I'm supposed to ask you how much it's over-filled or why you think it is over-filled. Since around the early to mid 90s, all engines use some oil between oil changes, and there were a lot of complaints from older drivers who were not used to seeing that. To address those complaints, you will see the markings on the dip stick no longer say "Add" and "Full". They say "Min" and "Max". We used to get excited when the level dropped 1/8th inch below the "Full" mark, and assume there was a problem. Today all manufacturers say if the level is still above the "Min" line at the next oil change, there's nothing to worry about.
Some mechanics purposely fill a little extra during the oil change service to insure you won't be worried if you check the level in a month or so and find it is down what you think is too far. That could be an extra half a quart and is nothing to worry about. What I WOULD worry about is two or three quarts too much. That has the potential to be just as serious as not enough oil. At high engine speeds the spinning crankshaft can hit the oil and whip air into it. That won't do damage instantly, but on a long high-speed highway drive, eventually that air will negate one of the oil's jobs which is to isolate moving parts from each other. Mostly that means pistons and cylinder walls, and crankshaft and connecting rod journals and bearings. Oil sprays onto the cylinder walls and is surrounded by air, so that isn't a concern, but the bearings won't survive very long without oil under pressure. Air can be compressed, and air in the oil can be compressed making it impossible for the oil pump to build the pressure to a safe level.
The main place you hear of seriously-over-filling the oil is at the "speedy lube" places where they have two or three people working on one car to get it done faster. Most of those people have a pretty good working rhythm and have very few problems, but sometimes you run into one where everyone thought someone else drained the old oil, or two people thought they were the only one putting the new oil in, so you get twice as much. Speed and lack of communication are the cause, so it's a good idea to check the level before you drive away. A conscientious mechanic will not take offense at your apparent mistrust, but they will appreciate a "thank you" when you're done. Part of the service is supposed to include checking the level. A person can become complacent after doing a hundred oil changes, but I will never admit that at least once I forgot to put the drain plug back in and pumped three quarts onto the floor, ... And my shoes. If two people each think the other one checked the level, what if it's that hundredth time that something went wrong? You don't want it to be the car owner who discovers the problem.
So again, how much is it over-filled?
Saturday, August 27th, 2016 AT 11:12 PM