Car Oils And Fluids

Why And What To Do When Oil In The Coolant Reservoir?

Mike Cross
Updated Aug 26, 2021
Why And What To Do When Oil In The Coolant Reservoir

As a car owner, you know that you need to perform regular maintenance on your vehicle to have it running its best. With regular inspection you should become familiar with how thigs should look under the hood. There are many tasks that you can do yourself, and some that a professional need to handle for you.

Yet even with diligence, issues with your car can and do arise on occasion. It is important to recognize when your car is having a problem, and then knowing how to resolve it. Along with the standard maintenance jobs such as checking the engine oil, fluids, and making sure tires are properly inflated, there may come a time when you see other signs of a problem lurking beneath the hood.

One of these problems can be oil in your coolant reservoir. This can be a major problem, so it is crucial to be able to recognize it, and then know the steps you need to take to resolve it. You should also understand how oil made its way into the coolant reservoir so that you can make sure it does not happen again in the future.

Why And What To Do When Oil In The Coolant Reservoir

What does the coolant do and how about the oil?

First you need to understand the functions of the coolant and the oil. Oil is a lubricant. It helps to lubricate the movable parts of the engine. As you drive, your engine gets incredibly hot. This heat helps to spread the oil onto the movable parts, keeping them lubricated.

Coolants are used to keep the temperatures in the engine steady and to cool down the combustion chambers so they don’t become overheated.

The engine is considered to be an inside part of the car and the coolant is in the outside part. Between these two sections is a gasket. The gasket acts as a seal. This seal protects the engine from outside elements that might cause damage. Btw, the engine will work fine with best synthetic oil 5w20, find the suitable for your vehicle.

What can cause the gasket to not work properly?

Brake fluid reservoir

Too much heat can and does cause damage to the gasket. This can happen because there is not enough oil, there is not enough coolant or you are running the engine at excessive heat levels.

What causes lead to the oil and coolant mixing together?

A broken or damaged gasket is the first culprit. And it is usually the most common reason why the two mix. If your gasket has any wear or tear, it will start to break down. This in turn affects how tight the seal is between the engine and the reservoir. Over time, more and more oil and coolant will be mixed together.

A damaged cylinder head is another reason why you might find oil and coolant together. You might have a damaged cylinder head if your car has been in an accident or if you have been overheating or overusing your engine. A cracked cylinder head should be fixed promptly to avoid the oil and coolant mixing together.

Some other causes that will allow the oil and coolant to mix are: damaged engine block, overheating and water entering the exhaust pipe or air intake valve.

How do you know if the oil and coolant have mixed together?

A quick check under the hood should provide with a lot of information. Your coolant fluid should be orange or green. If it is brownish, then you have a problem.

You can also use your car’s dipstick to look at your oil for clues. If you notice that there are brown bubbles or a dried crusty brown residue above the oil line on the dipstick, then the coolant has probably leaked into the engine of your vehicle.

It is possible that you might also notice that you suddenly have white exhaust smoke that has a sweet odor to it. This is also a sign that something is leaking somewhere.

How can I check for oil or coolant leaking?

If you suspect you have a problem you can take some steps to check. Before checking though, make sure your car is parked on level ground and has been shut off for at least 2 hours.

  1. Check for coolant inside the engine- this can be done visually looking at the dipstick and looking at the oil fill cap and valve cover. Use a flashlight to get a good look. If the oil looks to be a milky goo or yellow colored, chances are there is coolant in the oil. Most of the time this is because of a faulty gasket.
  2. Check for oil in the coolant- you can check for this by removing the radiator cap when the engine is cool. You should see very easily if there are puddles of oil inside the radiator. It is possible that you will also see oil in the coolant reservoir as well.

So now what do you do?

If you notice oil in your coolant reservoir you must replace the oil cooler and flush the cooling system.

If you have noticed coolant in your engine oil, then you probably need to have the head gasket replaced. Additionally, you should have your cylinders checked to be sure none of them are cracked or damaged.


Driving a car that is leaking oil into the coolant reservoir is not a good idea at all. In fact, if you suspect your car is having this problem, you should take it to a mechanic immediately. It will most likely be a costly repair, however, driving with oil or coolant leaking into parts of the engine will assuredly ruin your engine. This will then either cause you even more money in repairs or possibly render your car unsalvageable.

The best way to ensure this type of leak does not happen is by regularly examining your car under the hood. By becoming familiar with your car and engine and keeping a regular schedule of maintenance you can prevent a lot of bigger issues down the road. A little bit of time will help you enjoy your car for years to come

Mike Cross
Life is too short to drive with stock audio

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One comment on “Why And What To Do When Oil In The Coolant Reservoir?”

  1. Such kinds of malfunctions might not have any immediate outcome. But, may causes disastrous result if ignored. So, signs which indicate that the vehicle has such issues should not be ignored. Different types of fluids used in the vehicle should be subjected to inspection after a certain time interval and any signs which indicates that the vehicle has some sort of abnormalities should not be ignored. A car should be subjected to inspection after a certain time interval.

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