I must confess I have not changed my oil since I was 19 years old and poor. But now I'm back under the hood (per se) because I am sick and tired of the local Oil/Lube jocks diagnosing some "problem" with my Jeep every single time I take it for some clean oil. So the story begins like this ... I whip out the owners manual to find out how much oil my Jeep takes (3.7 L PowerTech V6) and it clearly states it takes 5 quarts if 5w30. Now for the drama ... I pull out my receipts from the oil change place to "confirm" the amount of oil needed for the Jeep and the receipt shows they've been putting in 6 quarts of oil! Now we all know putting more oil into your engine does not produce any benefits (like putting in more gas) ... to the contrary it can cause a great big headache! So after talking to the owner of the oil change facility it is decided that his employees have been over charging me for one extra quart of oil, but not actually putting the extra quart in ... nice huh?!?!
Now the reason I have turned to you guys ... what harm, if any, can come about from having an extra quart of oil in the engine during the past 4 oil changes? Since I changed the oil myself this last time the Jeep runs like normal ... actually my mileage has improved back to 17 mpg .... and I have noticed a little extra vibration at start up (sound like a clip is loose) maybe it was there before but never noticed.
Any insightful insight would be appreciated.