What Happens If You Fill Too Much Oil In Your Car Engine?

Too little engine oil is bad, and so is too much, as it can lead to severe problems. Here's a simple guide that explains the consequences.

Motor oil is a critical part of your car. You won’t be going anywhere without it.

Most people know that too little engine oil is bad – but what about too much? This will also cause severe problems (although it’s not as dangerous as the levels being too low).

In this guide, you’ll find out why overfilling engine oil is hazardous.

Table of ContentsShow

What Does Engine Oil Do?

Engine oil

Engine oil is refined from crude oil. It’s a thick (viscous) liquid that flows from the sump (oil pan) around the motor.

Its primary purpose is to lubricate the many moving metal components. It creates a cushion between two surfaces, preventing wear.

Engine oil also plays a role in cleaning the engine of impurities and assists the coolant system with heat dispersion.

Many people don’t realize the significance of motor oil. Without it, engines would grind to a halt within a couple of miles.

How Do You Check And Top Up Engine Oil?

Regular maintenance involves checking the levels and topping up your engine oil. It’s something every driver should be able to do.

  1. Park your car in a safe and flat (level) location. Put it in Park and leave the parking brake on.
  2. Open your hood and locate the oil dipstick.
  3. Pull it out and clean the end with an old rag or paper towel.
  4. Push the dipstick back into the engine (all the way) and then pull it out again.
  5. Read the oil level. It should be between the MIN and MAX marks.
  6. If your car requires a top-up, take a funnel and the correct oil multi-grade. You’ll find this in your owner’s manual. 5W-30 is one of the most common multi-grades.
  7. Open the oil cap (ti on the top of the engine.
  8. Pour a small amount in.
  9. Remove the funnel and place the lid back on your oil. Replace the oil cap on the top of the engine.
  10. Sit back in the driver’s seat and run the engine for 10 seconds. This pushes the new oil through the system.
  11. Go back to the engine bay and repeat the process (steps 2 to 5) with the dipstick.
  12. If necessary, repeat steps 7 to 11 until the oil level is between MIN and MAX.

It’s best to avoid overfilling it in the first place by being careful while topping up!

Do You Need To Pour In The Right Amount Of Motor Oil?

car engine oil fill port open

Yes.

Of course.

First things first. Every car takes a different amount of oil. They also take a specific type (multi-grade). You must get both of these correct – you’ll find the information in the owner’s manual.

If you’ve emptied your sump during an oil change, pour in precisely the amount instructed in the owner’s manual.

Before topping up with oil, check the dipstick. Add it a little at a time, remembering the oil will trickle down into the sump.

Run the car each time, and then use the dipstick to recheck the level.

How Much Oil Is Too Much?

You have ‘too much’ oil if the dipstick reading is above the MAX mark.

It’s as simple as that.

The oil level should be anywhere between the MIN and MAX marks. Contrary to popular belief, it doesn’t have to be touching the MAX mark.

The internet and the used-car industry are full of myths. These include suggestions that a certain amount of extra oil will be fine.

Don’t listen to them. The MAX reading on the dipstick is there for a reason.

In reality, you’ll probably – probably! – get away with a tiny bit extra. If it’s hardly noticeable, don’t worry. But if the level is clearly above MAX, you must drain it.

The manufacturer has set this limit on the dipstick because it’s the cutoff point at which they can guarantee the vehicle’s safety.

If you’ve overfilled your sump, the safe method is opting for a callout mechanic or a friend.

Alternatively, getting an oil drip pan and letting a little oil out through the drain plug will only take a moment. If you don’t have one, walk to your local store to get one.

What Happens If You Overfill Your Engine Oil?

Check Engine Oil

If you overfill your engine oil, the pressure in the crankcase will increase.

The oil level may start to submerge the crankshaft itself. It will get churned up too vigorously while the engine runs. This creates a frothy, air-bubble-filled oil, meaning it’s less effective and might damage the pump.

Your engine will sound louder than usual, including a distinctive ticking sound from the lifter. This is caused by air-contaminated oil.

In severe cases, the oil might find its way past the piston rings or contribute to them breaking. It’ll then get into the combustion chamber and start burning, producing an unmistakable odor.

Internally, this cakes the spark plugs, reducing engine efficiency. You’ll also see a blue tinge to your exhaust smoke, and your car will probably fail an emissions test.

On top of all this, the oil may start to leak. Check the areas around the pump, gaskets, and filter, in particular.

Finally, your car might have an oil pressure gauge. This could show you that the pressure is too high. Most other vehicles will simply see a Check Engine or oil warning light. A scanner will likely reveal a relevant OBD II code, such as P0520.

How To Drain Some Oil

This is best left to a mechanically-minded friend or a callout technician. Draining oil can be messy, and it’s easy to drain too much accidentally.

The mechanic will loosen the oil drain plug to allow a gentle flow of oil past. They’ll then tighten it back up and check the level.

Once the top of the oil sits between the MIN and MAX marks, your car is good to go.

You Might Love These Too

Symptoms Of A Blown Head Gasket
Symptoms Of A Blown Head Gasket
Benjamin Kitchen

Ben is an automotive author from England. With experience in a fast-fit garage, he's an IMI-qualified light vehicle technician. He aims to help drivers worldwide with common automotive problems. You’ll often find him working with his 1.2 Vauxhall Corsa – it may have a tiny engine, but in eight years it's never once let him down!