I put too much motor oil in my car's motor. About a quart - have I ruined my car? I've been driving it. I know I need to get the oil drained. But I'm worried that I've ruined my car which has been running very well until now.

  • It kind of depends on the cars engine oil capacity. A 3.5qt engine with plus 1qt is 25% over. A 10qt engine with 1qt over is 10% over I would prefer the 10% over but neither are good and continued driving is worse. Commented Sep 24, 2016 at 21:33

4 Answers 4


About a quart - have I ruined my car?

In short, no. If you read the answers on this similar question, even a gallon of extra oil generally won't ruin a car.

This is what I suggested and still recommend:

If the oil isn't hot, almost any sort of plastic tubing can be used for siphoning. It's easiest to go in via the dip stick.

Remember not to use the "suck start" siphoning method as you don't want a mouthful of oil. If you have a long enough piece of tubing, you can stick the excess down the dipstick tube, put your thumb over the end, pull out the slack (that is now full of oil) and you'll have an immediate siphon.

Also remember to siphon the oil back into the original container - you might as well keep it until you do need it.

It's not that big a deal. With an extra quart, most normal cars driven by normal people will just have slightly lower mileage due to pumping losses. Go ahead and get it back to the correct level, though: no need to waste gas or trouble your peace of mind.

  • If the car were driven for many miles (>100--1000), I'd be concerned about fouling the catalytic converter, which can get expensive. I didn't see anyone mention this point on this post or the linked post.
    – mac
    Commented Dec 3, 2012 at 23:49
  • 1
    @mac, fouling a cat? Why?
    – Bob Cross
    Commented Dec 4, 2012 at 2:02
  • 1
    my understanding is overfilling leads to increased oil consumption, which means oil smoke out the tailpipe, which can foul the cat. A couple of my vehicles have explicit warnings against overfilling on the oil filler that state something like "overfilling can lead to catalytic converter damage"
    – mac
    Commented Dec 4, 2012 at 15:01
  • 2
    @mac, if you consistently drove your car at +1 quarts, refilling every time the excess burned away, I would agree that additional exhaust components from the oil wouldn't be good for the cat. For a single overfill, that seems less likely. That said, this is all a game of risk management. If the driver is concerned about even a low probability outcome, the remediation procedure is clear: remove the excess.
    – Bob Cross
    Commented Dec 4, 2012 at 16:16
  • My spark plug wells get flooded causing engine misfire just after oil change.
    – KRoy
    Commented Dec 27, 2018 at 2:43

You most likely will not cause damage by running only an extra quart. Many people racing with stock oil pans will run half a quart to a quart of extra oil to prevent the oil pump pickup from drawing in air under racing conditions. Under sustained high RPM, oil can be pumped out of the sump faster than it can drain back. This issue combined with high cornering forces would move the remaining oil in the pan away from the oil pump pickup tube, causing oil starvation and engine damage.

Your engine's optimal maximum oil level is determined by filling up to where there is a safe gap between moving parts and the oil. What you put too much oil in your engine, you risk frothing the oil due to the crankshaft and connecting rods whipping air into it. The air bubbles in the oil will interfere with the oil's shear strength, which is what keeps metal parts from rubbing directly together. Not good.

Another problem is the additional oil splashing around the crankcase from the crankshaft and connecting rods whipping it up. It will coat the sides of the cylinder walls and could result in excessive oil consumption. In the worst case, carbon deposits from the burnt oil could cause the piston rings to stick, making oil consumption even worse and reducing power.

... but again, one quart is really not going to be enough for you to run into these problems. More than one quart is asking for trouble though. See: How far can I drive with 1 gallon too much oil?

  • Comparing racing a stock engine and daily driving conditions are not ideal to question asked. As you state a stock racing engine at higher then daily driving will maintain the excess oil in the upper levels. So the extra oil is still lower in pan. Most stock drivers replace pan with a higher volume pan keeping that oil at a lower level preventing crank and rods from reaching the oil body. Even very old engines with oil slingers did not want to let oil level get to high. But under daily driving and idle conditions with extra quart a much greater chance of foaming and oil to crank impact. Commented Sep 24, 2016 at 16:41

one quart probably not but 2 quarts ruined a 1984 Cadillac Sedan Deville. The excess oil had nowhere to go so it went passed the oil ring and up into the combustion chamber. The excess oil bent the exhaust valve. Very costly mistake.


It depends on your car. In many cases you may be fine – certainly if you've caught it and aren't seeing problems there is a good chance that you're OK or will only have relatively minor problems.

That said the folks who designed your car put a lot of thought into questions like "how much oil does it need?" and to be safe it would make sense to drain out the extra. Sucking it out through the dip stick tube may be the easiest way to do it if you have access to a vacuum extractor.

As a case in point where only a little extra oil can be a problem, VW Mk4 (1999-2003) cars with the ALH TDI diesel engine warn explicitly about putting in any amount of oil above the full mark due to potential catalytic converter damage (not fatal, but a few hundred dollars (US)).

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