Q: Car engine keeps shaking then it shuts off. Did I ruin it by accidentally putting too much oil in?

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My car was low on oil, I checked the dipstick and it was almost dry. Drove to pep boys and bought a gallon of 10 30 oil, recommended for my car. Stupid me, I did not know that when you put oil in the car, you pour a little in then check the dipstick to see if it's full. I thought it was how the water is, you pour it until it's full. I put about 4.5 quarts in it. After calling my dad, he told me I definitely should NOT have done that, I checked the stick and it was about an inch and a half over the full mark. Mechanic said it was shaking really bad when he moved it into the shop. I've never had an issue with that in the year I've owned it. The guys at pep boys drain it, and do an oil change. They also replace the air filter with my permission. After that is done, they try multiple times to turn on the car, then the engine proceeds to shake furiously then the car shuts off. In Park, Drive and Reverse. Every time they turned it on, same thing. Had to get it towed home. Any ideas?

My car has 120000 miles.
My car has an automatic transmission.

It certainly is possible that some engine damage was done. With the oil level reading an inch or more above the full line, it’s a safe guess that you were running at least 2 quarts overfilled. Considering the engine holds about 4 quarts, it was basically overfilled by 50%. With that much oil in the engine, aeration can be a problem. The oil will begin to foam or aerate due to so much oil in the small spaces inside the engine. As the oil aerates, the oil pump will have a hard time pumping the oil, oil pressure can drop and cause bearing, crankshaft, piston, and/or connecting rod damage as well as piston rings. A good place to check if the engine is still healthy is to have a local repair shop do a compression test. The readings can then be compared to factory specifications.

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