How To Fix Coolant Mixing With Engine Oil [5 Easy Solutions]

Are you wondering how to fix coolant mixing with engine oil? The most common reasons that cause coolant to mix with engine oil are a blown head gasket, cracked oil cooler, warped cylinder head, damaged engine block, and leaking transmission cooler.

Keep reading this article to find out more about these issues in detail and how you can fix them. We’ll also discuss the most common symptoms of coolant mixing with engine oil. Before we get started with that, you need to understand why coolant mixing with oil is bad for your engine. Let’s begin!

Why Is Coolant Mixing With Engine Oil Bad?

What does engine oil do? It lubricates the different components in an engine to make sure that they run smoothly without damaging each other.

What does coolant do? It cools down the temperature of the engine and keeps the engine from overheating. There could be severe engine damage if the car overheats and the coolant prevents that from happening.

But when coolant mixes with the oil, the viscosity of the oil gets changed. The texture and properties of the oil also change because one gets mixed with the other. The different components of the engine will no longer be properly lubricated with this coolant mixed oil.

If you keep driving your car with this coolant oil mixture, you can cause irreversible damage to your engine. In the meantime, the coolant level will keep dropping as it’s leaking and mixing into the oil.

So, the coolant would no longer do a great job at lowering the temperature of the engine and your engine will overheat frequently. That increases the chances of more engine damage and can even result in an accident.

That’s why coolant mixing with oil is a total nightmare for any car owner. When it happens, it needs to be addressed immediately and taken care of.

How To Fix Coolant Mixing With Engine Oil [5 Easy Solutions]

You’ll learn why oil is mixed with coolant and what are causes of this are in this section. Let’s look at the most common causes of coolant mixing with engine oil:

1. Blown Head Gasket

One of the most common reasons that cause coolant mixing with oil is a blown head gasket. Ideally, the coolant and oil flow in different parts of the engine without intervening with each other. The head gasket seals the coolant from entering the oil pan.

But when the head gasket gets blown or there are cracks in it, the coolant is no longer sealed and it leaks into the oil. You’ll notice the build-up of milky brown gooey substance when the oil mixes with coolant. Oftentimes, there will be white smoke coming from the exhaust pipe when the head gasket blows.

You can easily test if you have a blown head gasket by doing a compression test. If you don’t know how to do it, take it to a mechanic and he’ll do it for you and tell you if you have a blown head gasket.


A blown head gasket needs to be replaced but it can cost a lot of money. It’ll easily cost at least $1000-$2000 to fix a blown head gasket. Luckily, you can use a temporary solution to remedy the problem while you arrange the money to replace the head gasket.

Use a head gasket sealer like Bue Devil to prevent the coolant from leaking into the oil. Drain the mixture of oil and coolant from both the oil pan and coolant reservoir. When you put the coolant in, add the head gasket sealer with it.

Only use the head gasket sealer as a temporary solution. There’s no guarantee that it will seal the leak in the long run. If the coolant continues to mix with the oil and you keep driving in that condition, you can destroy the bearings of your engine. So, replace the head gasket ASAP if the one you have is blown.

2. Cracked Oil Cooler

The oil cooler in your car keeps the oil and cooler in different compartments. But if there’s a crack in the oil cooler due to wear and tear, it can cause the coolant to mix with the oil.


If you have diagnosed that you have a faulty oil cooler, you need to replace it. Luckily, you can replace the oil cooler on your own using a 12mm hex and pliers if you have some experience in working with cars.

Flush the coolant a few times before replacing the cooler to get the coolant mixed oil out of the system. Once you’ve drained it out of the system, change the oil cooler and you’re good to be back on the road.

3. Warped Cylinder Head

Apart from a blown head gasket and cracked oil cooler, a warped cylinder head is also a common cause of coolant mixing with the oil. When there are cracks in the cylinder head, the coolant can leak from the cylinder holes and get mixed with the engine oil.

The cylinder head can be warped from an overheating issue in the car. You should get that checked as well while you’re at it. Other common symptoms of a warped cylinder head are engine misfiring and roughing.


It was possible to work on the cylinder heads and repair them in older cars. But as most modern cars have cylinder heads that are made out of aluminum, they need to be replaced when there’s a crack in them.

Replace the cylinder head with a new one to fix the coolant mixing with the engine oil. It’ll be an expensive job but not as much as a blown head gasket.

4. Damaged Engine Block

If you have oil mixing with antifreeze, it can be caused by a damaged engine block. Fortunately, engine blocks being cracked isn’t common as they tend to be resilient.

But if a damaged engine block is causing the issue, you need to worry about it the most. That’s because replacing engine blocks can get expensive and doing that will put a hole in your wallet.


Inspect if you have a damaged engine block by taking it to a mechanic. If there are cranks in it, it’s a good idea to replace it. Replacing the engine block will cost anywhere between $4000 to $10,000 depending on your vehicle.

5. Leaking Transmission Cooler

Transmission coolers are prevalent in cars that have automatic transmission and they’re connected to the radiator. This cooler helps to keep the temperature of the hydraulic fluid down.

But when it gets cracked, it can leak the coolant and go on to mix with the oil. If this happens, the coolant can get into the transmission and damage it to an extent that it’ll need replacement.


How to stop coolant mixing with oil when you have a leaking transmission cooler? You need to replace it with a new one. It’s good to hire a mechanic to do that as it can be a tricky job to do for beginners. Replacing the transmission cooler will cost you between $250 to $500.

Coolant In Engine Oil Symptoms

How to tell if oil and coolant are mixing? The most obvious sign of a coolant leak is that you’ll see it spreading all over the engine. But if the leak doesn’t get that bad, there are some common signs that you’ll notice when there’s a coolant leak. Here they are:

1. High Oil Level

When the coolant leaks into the oil and mixes with it, the level of oil rises up in the oil pan because of the coolant. When you check the oil level with your dipstick, you’ll see that it’s beyond the safe zone.

As the coolant is leaking into the oil pan one way or another, it means that the coolant reservoir or the radiator will also be low in the coolant. If there are no external leaking issues, it means such a leak is internal.

2. Low Coolant Level

As the coolant goes to the oil pan, you’ll notice that the amount of coolant in the reservoir diminishes quickly. If you see a drop in coolant level but don’t see any leak making its way to the ground or the exhaust pipe, it’s surely ending up in the crankcase and getting mixed with the oil.

3. Overheating

When the coolant leaks and mixes with the oil, it not only messes up the viscosity of the oil but also doesn’t do a good job as a coolant anymore. It fails to keep the temperature of the car down and you will notice that your engine will be overheated when it happens.

4. Sweet Smell

Another way to tell if you have coolant mixing with oil is to sniff it. Pull the dipstick from the oil pan and smell the oil. When coolant mixes with the oil, it gives off a strong and sweet smell. If you smell that, it means the coolant in your car is leaking and mixing with engine oil.

5. Oil Color

The color of the oil will change when coolant leaks into it. It’ll depend a lot on the color of coolant you choose. However, the oil looks like a creamy coffee or chocolate milkshake in most cases when it mixes with a coolant.

You can check the oil color by using a flashlight if you don’t want to use the dipstick. If the oil looks milky, it’s because of a coolant leak.

6. White Smoke

Another sign of coolant mixing with oil is that you’ll see white smoke coming out from the exhaust pipe. Though it doesn’t always happen, it’s something you should know and be on the lookout for to tell if there has been a coolant leak.


What happens if you keep driving with mixed oil and coolant?

You risk burning down your engine if you keep driving when the coolant has mixed with the oil. You should address this problem and fix it soon to protect your engine from severe damage.

What to do if you accidentally put coolant in engine oil?

If you put coolant in engine oil by mistake and pour it into your car, you need to empty the oil from your vehicle using the drain plug. Put fresh oil back in and you’re good to go.

Can a damaged water pump cause oil in the coolant?

Engine oil never passes the oil pump as it’s designed to flow the coolant through the radiator, hoses, and the cooling system. So, a bad water pump won’t cause oil to mix with the coolant.

Can I use vinegar to flush my clogged radiator?

Vinegar is a mild acid that does a great job of getting rid of rust. Put vinegar along with a gallon of water and turn on your engine. Keep it running for 30 minutes at idle to flush the radiator.


It can be frustrating to notice that your engine oil has turned into a milky liquid after getting mixed with the coolant. But now you know how to fix coolant mixing with engine oil using this guide.

Find out the exact issue that’s causing the coolant to mix with the engine oil and get it fixed to drive your car without worrying about engine damage. Leave a comment below if you have any questions about coolant mixing with oil.

About John M

John contributed as a technical head at an automobile company just 2 years after his post-graduation in Automobile Engineering. He loves to lead a free life, so he left his job & started blogging. Now, he does research on every automotive problem, part & product and seeks a better solution & best products & shares his findings with his readers to help them as well as to minimize their struggle.

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