What Happens If You Fill Your Car’s Engine With Too Much Oil?

Most people know that your car’s engine needs oil to run properly. But what if you add too much oil into your car’s engine? What happens then?

So what happens if you fill your car’s engine with too much oil? If you’ve accidentally added too much engine oil to your car then you’d first see smoke coming out of the exhaust of your car. It’s likely that your spark plugs will be coated in oil and need to be replaced. Your engine will also be running rough and backfiring, it may even stall out and quit running altogether.

But what next steps should you take if you’ve filled your engine with too much oil? What are the symptoms of adding too much oil to a car? What’s the easiest way to remove excess oil from an engine? Keep reading to find out.

What Happens If You Fill Your Engine With Too Much Oil?

Your car’s engine is designed to keep a certain amount of oil inside of the engine that circulates throughout it to keep the moving parts inside well lubricated.

Overfilling your engine with oil will allow engine oil to circulate into areas that it should not, including into the combustion chamber and onto your spark plugs.

As you can imagine having oil coated on your spark plugs will cause your engine to run poorly and can cause the engine to sputter and die.

Excess engine oil will also cause your engine to work harder as it has to move around more oil than it’s used to. Overfilling your engine oil can also cause the engine oil to become foamy and reduce the lubricating effect of it.

Can Too Much Engine Oil Damage Your Engine?

The short answer is that yes, adding too much engine oil can cause damage to your engine if left in the engine for long enough. Excess oil in the engine will

1. Fouled Spark Plugs

Adding excess oil to your engine will cause engine oil to get into the engine cylinders and onto the tips of your spark plugs causing the tips to foul up. When too much engine oil is added to an engine it will force oil into areas of the engine that it should not be in, like inside the engine cylinders. Expect to need to replace your spark plugs if you fill the engine with too much oil.

2. Plugged Catalytic Converter

Adding too much oil to your engine can also cause excess oil to be sent out the exhaust system which can plug up your catalytic converters. Engine oil that enters the engine cylinders will be expelled out the exhaust port with the exhaust gases. This will cause your catalytic converters to plug up and be rendered useless causing your engine to run poorly.

3. Fouled Oxygen Sensors

Oxygen sensors can also be damaged by adding too much oil to your engine. Excess engine oil can be sent out to the exhaust ports of your engine and can cause your oxygen sensors to no longer work properly. Once your oxygen sensors go bad your engine will run rough until the oxygen sensors are replaced.

4. Bent Rods or Valves

A certain amount of oil is designed to be in the engine at all times. When too much is added it can cause issues with oil pressure inside the engine. This can cause damage to your engine piston rods and valves. Once you break a piston rod or bend a valve you would need to have your engine rebuilt or replaced.

5. Blown Engine

Having too much oil in your engine will cause the engine to work harder which can cause significant engine damage. Varying engine pressure and getting oil into places that it should not be is not good for an engine, especially the longer you have it running in that state. This may result in having to have the engine rebuilt or replaced.

Now that you know how adding too much oil to an engine can damage it what are the symptoms to look out for to tell if your engine has too much oil in it?

Top 5 Overfilled Engine Oil Symptoms

1. Dipstick Oil Level Is High

The easiest way to check to see if your engine is overfilled with oil is by checking the dipstick if your car has one. The engine dipstick should have a high and low indicator on it to show you what the optimal level your engine oil should be at.

If your dipstick reading shows that your engine oil level is well above the high level then you likely have too much oil in your engine and some oil will need to be drained out.

2. Smoking Tailpipe

Another indicator that your engine has too much oil in it is that you have smoke coming out of your tailpipe. If there is too much oil in your engine it will cause engine oil to get into the combustion chamber.

Since engine oil isn’t designed to be burnt along with the air and fuel mixture in each cylinder it will escape the cylinder in the form of smoke and out through your tailpipe. Noticing smoke coming out of your exhaust when the car is running can be a sign that you have excess engine oil in your engine.

3. Backfiring Engine

Adding too much oil to your engine can cause your engine to run rough and backfire as well. Since engine oil will be circulating throughout the engine in areas that it should not like the engine will not be running that well and can even cause it to backfire. If you notice that your car is backfiring it’s a good idea to turn off your engine to investigate why your engine is backfiring.

4. Oil Soaked Spark Plugs

Overfilling your engine with oil can also cause your spark plugs to be soaked in oil. Oil is designed to lubricate the pistons as they move up and down each cylinder.

But if too much oil is added to the engine oil can find it’s way inside of the cylinder and onto your spark plugs. As you can imagine having oil on your spark plugs is not ideal when you need them to create a spark to keep your engine running.

If this has happened to you then you’ll likely need to replace all of your spark plugs as they will have been fouled up from the oil inside of the engine cylinders.

5. Rough Running/Stalling Engine

I’ve already talked about how oil can get into areas it shouldn’t if you overfill your engine with oil so your engine running rough probably won’t come as a surprise.

Problems with excess oil in your engine can foul up your spark plugs and cause your engine to work harder than it’s used since it’s pumping all of this extra oil throughout the engine. Any problem with the air/fuel mixture, or with the spark can cause your engine to run rough or sputter.

What Should You Do If Your Engine Has Too Much Oil In It?

If your engine is overfilled with engine oil you’d want to drain the excess engine oil to the correct oil level for your engine. All cars will come with an oil drain plug that is used to drain old oil that then allows the engine to be filled with new engine oil.

If you just filled up your engine with new oil you wouldn’t want to drain all of it you’d only want to drain enough to get it to the proper fill level. If your engine oil is older then you could go ahead and drain all of the engine oil and replace it with new oil.

Just make sure that you check the engine oil fill levels to make sure that they are in the proper range and the oil is not too low or there is still too much oil in the engine using your oil dipstick in the engine bay of your car.

How Much Oil Is Too Much On The Dipstick?

Most cars will come with an engine oil dipstick that can be used to check the engine oil levels. This dipstick will be located in the engine bay and will be located near the engine. When you look at your engine oil dipstick there will typically be a crosshatch section or two holes to indicate what the engine oil level should be.

The oil dipstick that came with my car (pictured above) has two holes to indicate the high oil level and the low oil level. As long as the engine oil level is between those two holes (or within the crosshatch section on other dipsticks) the engine oil level is fine.

If the oil level is above the top hole that means that there is too much oil in the engine. If the oil level drops below the bottom hole then more engine oil needs to be added. Not all dipsticks are made the same and some are meant to have the oil level read when the engine is hot or cold so make sure to keep that in mind when inspecting your dipstick.

The dipstick that came with my car does not mention if it should be read while the engine oil is warm or cold so it should not matter either way.

Is It OK To Slightly Overfill Your Engine With Oil?

Yes, it’s fine to overfill your engine oil with a half quart to a full quart of oil but you wouldn’t want to overfill your engine with more than one quart of oil. If your engine is older and is starting to burn oil then you may want to add a bit more oil (1 quart) than normal the next time you fill your engine with oil.

That way you can extend the time between needing to fill your engine again with oil. If your engine is newer and isn’t burning much oil then you’d want to keep your oil levels within the ranges shown on your dipstick.

Will The Oil Light Come On If There Is Too Much Oil?

Most oil light sensors are designed to check the oil pressure levels and then illuminate if the pressure sensor detects low oil pressure. So on most cars, they won’t be able to detect that the engine oil level is too high as additional oil won’t cause the oil pressure to drop.

Can I Drive With Too Much Oil In My Engine?

When it comes to driving with too much oil in your engine it really comes down to how much additional oil is in the engine. If you know that the oil level is a quart of oil above where it should be then it won’t damage your engine.

But if the engine oil was filled all the way to the top of the oil fill port then driving with that much oil in your engine could definitely damage the engine depending on how long the engine runs.

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