Oil in Coolant: What To Do & Causes

When you go to change your coolant and realize you have oil in the coolant, most people start to panic and wonder if their car is going to break down soon. In this blog post, we will go over the causes, effects, and what you can do to help your vehicle.

How To Tell if there is oil in your Coolant Reservoir?

The Texture of Coolant:

Oil in the coolant can alter the texture of your coolant making it a slightly different color and feel. If you look at the side of your coolant reservoir at home or simply turn your car on and let it idle for a few minutes, then pop open the cap to your coolant reservoir to see if it has a film on top of it. This would indicate oil in your radiator fluid.

Opening a radiator cap.

Smell Of Your Cooling System:

Next to the texture is its smell, if there is a sweet smell coming from inside or around the engine bay this could signal that there is oil in your cooling system from either an external leak somewhere on the car, a blown head gasket, or a bad seal.

Oil is Running Low:

If your oil level is running low and you keep adding it and the level keeps going down, this could show that there may be an internal leak somewhere on the engine.

5 Causes of Engine Oil In The Coolant Reservoir

Cracks in the cylinder head

The first causes cracks in the cylinder head. The metal that separates the engine oil and coolant is typically made out of cast iron. As the engine gets hot, it expands, when it cools down, it contracts.

Car engine cylinder head.

This process can cause tiny cracks in the cylinder head which can leak small amounts of engine oil into your coolant reservoir. Since this type of crack is usually on older cars, you should get to a mechanic ASAP to get it inspected before you cause more damage to your car.

Cracks in the engine block

The second causes cracks in the engine block. The engine block is the middle part of your engine where all four cylinders are. The coolant flows around this metal cylinder to keep everything nice and cool. If there are any cracks this could allow for small amounts of engine oil to leak into your coolant reservoir.

Auto mechanic adjusting cylinder head on the engine block at the workshop.

Faulty Transmission Fluid Cooler

The third cause is faulty transmission fluid cooler lines. The transmission cooler is what cools the fluid inside your automatic transmission. If this part becomes damaged or if it leaks then engine oil could mix with the automatic transmission fluid and create a very dangerous mix.

The danger behind this type of mix is that the engine oil can make it impossible to shift from gear to gear correctly in an automatic car. This creates lots of issues for people as they constantly have to stop, manually put their car into park and restart. Not a good situation.

Faulty Oil/Coolant Heat Exchange

The fourth cause is the oil/coolant heat exchange. This part is usually found in newer cars and it takes any engine oil that makes its way into your coolant, collects it, and then routes this oil back to your engine where it belongs. If there are any cracks or faulty tubes in this heat exchange it could allow for small amounts of engine oil to mix with the antifreeze inside your cooling system.

Damaged Head Gasket

Finally, the fifth and most common cause is a damaged head gasket. The head gasket simply keeps your engine from leaking fluids out of their respective areas. If there are any cracks or broken areas in this part it will start to leak oil into the coolant system as well as antifreeze into the engine oil. This type of problem leaves you stranded on the side of the road with no one to call for help.

Blown cylinder head gasket.

What to do if you have Oil in the Coolant Reservoir?

You should drain and clean the reservoir, you need to identify the source of the leak. If it is external, you will need to replace or repair broken parts like gaskets or hoses. If this does not work, then you may have a cracked engine head and in that case, the only thing to do is replace it.

Can you drive a car with oil in the coolant?

Coolant and oil should never be mixed, as they reside in separate compartments in the engine. Driving a car with an incomplete mix of coolant and oil can cause significant damage to your engine, possibly necessitating costly repair or complete motor replacement.

Why is the mixing of these liquids harmful for the engine?

Since the coolant and oil reside in separate compartments, mixing them can compromise or even damage the engine. Oil is responsible for lubricating all of your car’s parts, including its internal engine components.

The engine needs this lube to stay protected from heat-related damage that could result either from normal operation or stalling. Thus, adding antifreeze into your crankcase will lead to reduced protection for your vehicle’s moving parts. Mixing these liquids can also cause overheating problems, as well as issues related to the car’s performance. If you want to protect your automotive investment, keep these two types of fluids apart.

How do I get rid of oil in my coolant system?

If a complete engine overhaul is not an option, you should drain and clean the reservoir, as well as fill it with water and flush the radiator. You should also inspect your oil dipstick to see whether there is an oil-coolant mixture in your engine’s tank.

If this is the case, you’ll need to replace your oil as well.

How much does it cost to fix oil in coolant?

The pricing is not too bad for this problem, but it can vary depending on the shop and your location. On average it should cost around $200 to $500 to get this done. If you need a new engine you can expect that price to be raised due to the damage you have done.

How long does it take for oil in cooling system repairs?

The time is usually very quick on these types of problems unless there are other issues with your car. Most shops can do this in two hours or less which makes this a very easy fix.

Here are some ways to keep your car from leaking oil into the coolant system.

Check all fluid levels regularly. Make sure the oil and antifreeze levels are topped off to make it easier for any leaks to be seen. If possible, check the levels when you first start your vehicle up in the morning as well as before you turn it off at night. This way you can catch a leak early on if one does happen – instead of waiting for an issue that could end up worse by later in the day.

Oil dipstick.

Keep detailed logs of when you do this routine so you have a track record going back many months. That way if there is a problem, you will know how long it has been going on and have proof to show the shop. You can even take pictures to document this process as you do it.

If possible, park your car on a level surface so any leaks will be found quickly and won’t drain your vehicle’s oil – or coolant – which only makes the problem worse.

Don’t forget to service important parts such as spark plugs, filters, and brakes at recommended intervals for best performance and maximum longevity of components.

If you have a car that is leaking oil into your cooling system there are a few things that need to be done in order for it not to cause harm to the engine.

  • The first thing should be bringing it into a local mechanic or dealership if you cannot do anything yourself. This article gives great advice for those who want.
  • When you add fluids to your car, be careful. Oil goes in the oil fill, while coolant goes in the overflow tank. And put on all of the caps right when you are done filling them. If you are not sure, just take a second to check before doing anything.
  • When you fill the fluids in your car, do not fill them up all the way. Your car has different fluids that need room to expand when they get hot.
  • You can use a sealant additive to help the seals in your engine stay good.
  • Listen for changes in the sound of your car’s engine or when you are driving. This might be a sign of trouble with the car.
  • Avoid overheating your car engine. Watch the temperature gauge. If you see drips under your car, try to figure out what kind of fluid is leaking. Check your fluid levels often and investigate any sudden changes in them.

How much does it cost to fix oil in coolant?

When you notice the presence of oil in the coolant of a car, you have to pay attention immediately. How much does it cost to fix oil in coolant depends on several factors, and in any case, it is a failure that is not cheap to fix.

Generally, it is a broken cylinder head gasket, and to repair it is necessary to disassemble the cylinder head, replace the gasket with a new one, and perform an efficient cleaning of the entire cooling system of the vehicle. This means at least 12 hours of work of a trained professional, we can be talking about a cost that can range between $675 and $1250, it may be higher or lower depending on the model of the car.

However, knowing exactly how much does it cost to fix oil in the coolant will depend on the degree of damage that has been caused to the vehicle, if it has circulated excessively while the breakdown has occurred, the damage may be greater, and that means that the cost of repair will increase.

How do I know if my Head gasket is blown

Knowing the basic operation of a vehicle is vital, especially for vehicle owners. Knowing how to identify the symptoms of a possible failure can be a great advantage and will save you the hassle, time, and money.

For example, finding the answer to “How do I know if my head gasket is blown?”

Blown cylinder head gasket.

There are several answers to this question:

  • The first symptom that this Head Gasket is blown is the constant overheating of the engine.
  • The presence of coolant drops in the oil, this is noticed when you take out the oil dipstick, and in it, you observe the coolant drops.
  • When the smoke coming out of the exhaust pipe is white.
  • You observe oil in the radiator and in the radiator cap.
  • Loss of coolant.

It is necessary when observing any of these symptoms to pay immediate attention. This joint is the one that guarantees the impermeability of the engine. To attend to the failure, and to repair it in time will avoid serious damage to the engine’s extra expenses that its repair entails.


If you suspect you have an oil-coolant mix in your engine compartment, you need to check your dipstick immediately. Moreover, if there is a sweet smell coming from the exhaust or the car has started overheating, these are further indicators for you to inspect your vehicle’s liquid level and color. If you notice that your liquid levels are low, then it’s time to take action before any damage occurs.

If you found this blog post helpful, please share it with your friends! If you have any questions or further tips to prevent this problem from happening, let us know in the comment section below. Don’t forget to subscribe for a free weekly newsletter on all things automotive!

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About Matthew Webb

Hi, I am Matthew! I am a dedicated car nerd! During the day, I am a journalist, at night I enjoy working on my 2 project cars. I have been a car nerd all my life, and am excited to share my knowledge with you!

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