What Happens When You Overfill Your Car With Oil?

Key Points

• Too much oil can cause low oil pressure just like too little oil.
• A ticking sound or a low oil-pressure light could indicate too much oil is in the engine.
• Drain off excess oil to avoid damage to your engine.

While having too little oil in your engine can understandably cause problems, having too much oil can be just as bad. In both cases, low oil pressure can result, potentially causing severe engine damage. 

Related: How Much Oil Consumption Is ‘Normal’?

Symptoms of Too Much Engine Oil

Key Takeaways:

• Oil moves from the oil pan underneath the engine, up through the oil pump and into the engine.
• Too much oil can lead to it frothing and causing oil-pressure warnings and possibly a ticking sound.

In almost all cars, the oil is carried in a deep pan underneath the engine — it’s appropriately called the oil pan. When the engine is started, an oil pump sucks up oil through a filtered pickup tube that sits beneath the top surface of the oil. It pulls oil from near the top to avoid sucking up sludge and water that may have accumulated and sunk to the bottom of the pan. The pump then circulates the oil throughout the engine, after which the oil falls through drain holes and back down into the pan to begin the process anew.

The top surface of the oil in the pan sits right beneath the engine’s crankshaft. The crankshaft has irregular projections in the form of crank pins, which connect each piston to the crankshaft, and counterweights that help counterbalance the weight of the crankpins. The crankshaft spins whenever the engine is running. For instance, at 2,000 rpm — about the speed the engine is commonly turning — multiple crank pins and counterweights pass over the top of the oil 2,000 times per minute, or 33 times per second.

That is, unless the oil level is too high.

If the oil level is too high and the crank pins and counterweights contact the top surface of the oil, the constant slapping of the oil surface can froth up the oil and turn the surface into foam — right where the oil pump is trying to pick up oil. Oil pumps don’t pump foam very well, so oil pressure drops and parts of the engine get starved for oil.

Besides triggering the oil-pressure warning light or showing low pressure on the oil-pressure gauge, frothing might make itself known by a constant ticking sound from the valves. Valves typically sit at the top of the engine and are therefore the first parts that suffer from low oil pressure. (This is also true if your oil level is too low.)

If you hear ticking while driving, first check to see if the oil-pressure light is on or the gauge is reading low. If so, it’s best to pull over as soon as it’s safe and shut off the engine. Wait for a few minutes for the oil to drain back into the pan (and the engine to cool a bit), then open the hood and check the oil level on the dipstick. Make sure you’re on level ground to get an accurate reading. If the oil level is too high, it’s best to remove some oil, either by draining it out through the drain hole in the oil pan or getting a hand siphon pump with a long, thin hose that goes down the dipstick tube. 

Note that many newer cars don’t have oil dipsticks anymore. Instead, there’s an electronic sensor that detects the oil level, generating a readout that’s typically accessed through the car’s touchscreen. (It can be a little tough figuring out how to find it on the screen’s menu, but looking under “Oil” in your owner’s manual or doing an internet search for “How to check oil level in a year/make/model” should tell you how.)

How Did Too Much Oil Get in There?

• Key Takeaway: Gas or coolant leaks, improper oil filling techniques and issues with the dipstick can cause the oil level to be too high.

Adding too much oil often occurs during an oil change.

Shops commonly get their oil in huge barrels rather than quart or gallon containers, and the engine is filled with oil through a hose similar to what’s on a gas pump. This is both cheaper and faster, but if the trigger on the hose is held too long — or the mechanic misread how much oil was needed — too much oil can be put into the engine. Shops often don’t check the oil level afterward, partly because it takes a few minutes for it all to run down into the pan. (And you expected this to be done in 30 minutes, right?)

Similarly, if you’re changing the oil yourself (or even if a shop is doing it), the manual might say the engine takes 5 quarts, but that’s if the oil filter is also changed — and the oil filter can hold the better part of a quart itself. So if you don’t change the filter, that 5 quarts may be nearly a quart too much. 

If your engine burns oil between changes — and for some cars, that’s considered normal — you might check the oil when the engine has just been shut off before oil has returned to the pan and added too much. By the way, if your engine burns oil and you’re tempted to overfill the oil so you don’t have to add it as often … don’t.

Also, although the oil level might read too high, excess oil may not be the culprit. If you have a head-gasket leak, coolant can find its way into the oil pan and mix with the oil, raising the oil level and diluting it. A fuel-system leak can also cause gasoline to seep into the oil pan, which also raises the oil level and dilutes it. If you have a dipstick, coolant will usually leave a foamy white, sweet-smelling substance on it, while gasoline usually emits its familiar smell, and in both cases, the oil will seem really thin. 

There’s one more possibility, albeit slim: It’s possible that the dipstick reading is wrong. This can happen when the little cap at the top of the stick, which is supposed to seat when the dipstick is fully inserted, has been moved up, pushing the stick down farther into the oil and resulting in a high reading. The oil could have also been overfilled because the dipstick didn’t seat completely when it was last checked, which would give a low reading and prompt more oil to be added than should have been.

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What to Do If You Have Too Much Oil

• Key Takeaway: If you have too much oil, drain off the excess oil using the drain plug or a siphon.

Ideally, if the oil level is found to be too high and it doesn’t appear as though leaked coolant or gasoline is to blame, it’s best to drain out all the oil then pour it back in, stopping with at least a quart or two to go. Let things sit a few minutes, then check the oil level on the dipstick or your touchscreen, and keep adding oil until you get it to the full mark. You should have some oil left over.

In an emergency situation, you can try to drain out a little oil through the oil-pan drain plug, replacing the plug after a quart or so of oil has drained out. Note, however, that the oil will be hot unless you let the car sit quite awhile. You’ll need the proper size wrench for the drain plug, a pan to catch the oil, a big bottle to carry the excess oil and a rag, as it will be a messy job.

A more convenient but less likely option is the aforementioned hand siphon pump. These can be found at auto-parts and sometimes big-box hardware stores, but you’ll need to carry it with you (or have it brought to you), and you’ll still need a big bottle to carry the excess oil.

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