What Happens When You Put Too Much Oil in Your Car?

Thom Blackett | Apr 16, 2020

Aside from filling the gas tank, changing a car’s engine oil is perhaps the most common task required to keep a vehicle running properly. This bit of routine maintenance can be done by a quick-lube station during your lunch break, at the dealership while running errands on a Saturday morning, or even in your own driveway after work. Fresh oil is an engine’s best friend, but too much of it can cause costly damage and should be removed as soon as possible.

What Happens When You Put Too Much Oil in Your Car?

Dangers of Overfilling the Engine Oil

To understand how overfilling your engine oil is too much of a good thing, it’s helpful to first provide a little background.

Engines are comprised of hundreds of precision-crafted parts working in unison at high speeds and temperatures, all of which require oil for proper lubrication and smooth movement. You, or your mechanic, add oil to an engine to the crankcase via the cap labeled “Oil” under the hood. The oil settles in the oil pan when the engine is not running. When you start the engine, the oil circulates throughout the engine and passes through an oil filter that removes contaminants that could potentially cause damage.

When too much oil is added, the level in the oil pan becomes too high. That allows a fast-moving lobed rod called the crankshaft to come into contact with the oil and essentially aerate it. The result is a foamy, frothy substance that cannot properly lubricate the engine. Think of this as your engine’s way of turning cream into whipped cream. No one wants whipped cream lubricating their engine.

Also of concern, the extra oil creates excessive pressure inside your engine that will look for an escape through various gaskets and seals. If one or more of those fail, that will lead to leaks and costly repairs.

Potential Causes of Excess Oil in Your Engine

When investigating why there’s too much oil in your engine, there’s one blatantly obvious answer: either you or your mechanic overfilled the crankcase when topping off or after an oil change. Along those same lines, failing to properly drain old engine oil when doing an oil change, or adding too much oil to the new filter, could also be the culprits.

If those simple mistakes didn’t cause the problem, you may find that the extra “oil” is actually a combination of fluids. Condensation can build up inside an engine, fuel can get past a faulty seal, or a failing head gasket can allow coolant to leak. In any of these scenarios, you’ll have an excess of diluted oil that can cause serious damage.

How to Determine if Your Engine Has Too Much Oil

If you suspect you have too much oil in your engine, the quickest way to get an answer is to look at the dipstick. With the exception of some high-end exotic models, this simple part is found in all types of cars, typically has a bright yellow pull handle, and features low and high marks to show if your car has too much, too little, or the perfect amount of oil. It’s advisable to get into the habit of checking the level frequently, and always after an oil change. Consult your owner’s manual for specific guidance on checking your car’s dipstick.

There are other indicators that will suggest you have an overfill problem, including blue exhaust smoke, a burning smell, an oil leak, or a high reading on your oil pressure gauge (if equipped). If the engine is running rough or your check engine light illuminates, the cause may be excess oil contacting the spark plugs and causing a misfire.

How to Remove Excess Oil from Your Engine

Some backyard mechanics suggest siphoning excess engine oil from the dipstick or crankcase cap, but we recommend a safer and more precise method. Perform a fresh oil change.

If you’re comfortable doing your own oil change, you’ll remove the oil drain plug at the bottom of the oil pan, completely drain the engine of oil, remove and replace the oil filter, and refill the oil with the proper amount specified in your owner’s manual. Naturally, you’ll need a drain container to collect the oil and dispose of it properly (local recycling centers and auto parts stores usually charge a small fee to accept used oil). Also, remember that if you’ve been driving the car before the oil change, the oil is likely hot and could cause burns if you don’t handle it appropriately.

If you would rather have this service completed by a mechanic, consider having the car towed to the repair shop to avoid possibly causing engine damage during the trip.

Compare Cars Before You Buy

Operating an engine with excess oil can lead to costly repairs. If your vehicle is in need of replacement, use JDPower.com to research and compare cars before your next purchase.

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