Yes, overfilling can cause a problem, although chances of severe engine damage would not be foremost on my mind. A little overfull isn't a big deal either. Most dipsticks no longer have "full" and "add" marks because there were too many complaints from the level being not exactly perfect. Today they use "min" and "max". As long as the level is somewhere in between the two, it's ok.
If the level is overfull enough, rotating parts will whip air up into the oil. Air compresses, oil does not. Oil's purpose is to isolate moving parts from each other. Air reduces oil's ability to do that, but it doesn't eliminate it completely. In MOST cases, bearings will not be damaged right away from air in the oil. That's a longer term thing. Even though it's not good, at least oil is getting to the bearings.
Hydraulic lifters, on the other hand, need air-free oil to do their job. They expand and contract to take up slack in the valve train that changes dimensions as the parts warm up. Two main parts of the lifter are filled with and separated by oil. The oil is just as hard as steel. When there's air in the oil, it can compress. Parts start to move, and rather than moving their mating parts, the slack is taken up, then the first part bangs into the second part before it starts to move. That banging is what you're hearing. Similar to pushing a piece of steel with a hammer, (quiet), vs. Running the hammer up to the steel to make it move, (clank!). Other than the irritating noise, this isn't going to cause damage right away. Eventually the banging will hammer out mating surfaces of some of the parts. Then the valve train will be noisy even when there's no air in the oil. I would expect this kind of damage to take hundreds or thousands of miles.
My suggestion is to take the vehicle back and politely thank them for changing the oil, but explain that they were too generous and you'd like to give some of the oil back. That will set the tone for a cooperative visit, and don't be surprised if they offer you a free next oil change, a car wash, or some other tangible form of apology. They will know a mistake was made and they'll want you to know you can trust them in the future. At the very least, if you never go back, they deserve to know what is happening to cause them to lose business.
If you are angry and accusatory, you will get the same service done to your car but you will be treated as the adversary, not the partner in your car's maintenance. If you show you are not upset, they are more likely to bend over backwards to make it right. They must remember that you had to take time out of your busy schedule to come back a second time. It may never come up in the conversation, but they are definitely aware of it.
Understand too that the way a lot of the speedy-type oil change places accomplish the fast service is to have two or three people work on your car. If they don't have a well-practiced routine, or if they don't communicate well with each other, each one could put the oil in, so you'd have twice as much as it should be. That's not a valid excuse on their part, just one possible explanation. They should be checking the level before they finish. That rarely happens at dealerships and full service independent shops because it's almost always just one person working on your car.
Consider returning when you can offer to wait a while longer than normal. The oil will be really hot. That's not a problem when they remove the drain plug then stand back and let all the oil out. For this service, they will drain just a little, then try to put the plug back in while the hot oil is running on their hands! No one likes burning oil. If you can go shopping nearby, an extra half hour, Im sure, will be appreciated.
Tuesday, March 2nd, 2010 AT 11:17 PM