February 11, 2009 12:49 PM   Subscribe

Is too much oil in a car engine something to worry about?

I got an oil change in my 1997 Citroen Saxo today, and they managed to overfill it by about half a centimeter as measured on the dipstick. I am wondering if there might be any negative side effects, apart from the waste of oil, as there must be a reason for having both MIN and MAX markings on the dipstick.

In general, the engine runs along nicely without any perceptible oil loss, so I do not expect the extra oil to go away until it's time for the next oil change.
posted by ghost of a past number to Technology (6 answers total)
I believe you can blow out various seals in your engine with too much oil, but you should be ok with a half a cm. Still, I'd take it back and make them redo it.
posted by electroboy at 12:52 PM on February 11, 2009

Best answer: In general a small amount of overfill is not a problem. If there's quite a bit too much, then yes, it could be a bad thing:
As the crankshaft rotates it will churn the oil, causing aeration and eventually sustained foam may form. This can lead to overheated motor oil, oxidation and a loss of oil pressure. Spongy aerated oil is hard to pump. It starves the engine and critical lubricated surfaces.

A google search for "oil overfill" will turn up more information than you ever wanted to know.
posted by chrisamiller at 12:53 PM on February 11, 2009

A dipstick isn't exactly a precision measurement instrument. 0.5cm seems within a reasonable margin of error. Oh, was the engine cold or warm when you checked, because that could add to the imprecision?
posted by Good Brain at 1:16 PM on February 11, 2009

Best answer: Mountain, molehill. If it was drooling out the dipstick hole, you'd have a problem. Wors case, you get a little frothing in the crankcase until the excess is purged through the slow process of there being to much oil thrown up onto the cylinder walls and burning off.
posted by notsnot at 1:16 PM on February 11, 2009

Response by poster: Many thanks for the speedy answers. Any time you need a ride, let me know.
posted by ghost of a past number at 1:20 PM on February 11, 2009 [1 favorite]

I once overfilled an engine. The dipstick tube wasn't installed right or crimped when the previous owner had some work done to the car, so it looked dry... I added a quart, and at the next gas station, added one more when the stick still looked dry.

Then the engine caught fire.

No shit. That "froth" seeped out of every place in the engine it could, the filler cap, vent tubes, you name it, and then started to burn when it hit the manifold. There was oil everywhere inside the engine compartment when I beat the flames out with my jacket. Towed the fucker home, drained five quarts from the engine, and spent two days cleaning the sixth quart from under the hood. (This was a little Ford Festiva. Put in four fresh quarts and it ran like a champ another five years.)
posted by Slap*Happy at 6:57 AM on February 12, 2009

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