What Should You Do When Oil in Coolant Reservoir?

In general, most of us understand that oil in the engine should never mix with the coolant or water. If it does so, you need to pay attention to something that is going wrong with your car.


To learn more about this problem, you need to know the basic function of the engine to easily identify the types of issue that would be persisting in the system.

What Do Coolant and Oil Achieve?​

Basically, oil is a lubricant which is normally applied to lubricate various movable components in the engine, which produces a great amount of heat because of generated energy.

To cool it down, coolant is used to keep the engine’s temperatures under control and stable. In a truck, car or any other vehicle with 4 wheels, the engine is made in a rather peculiar design so that it could be fully covered with a top that might keep the engine from foreign elements.

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Common Reasons for Oil in Coolant Reservoir​

The most common cause that most of the car owners often guest is the failing of head gasket in the engine, but there would be other particular reasons that cause this malfunction to occur as well.

According to some engine experts and professional mechanics, some of the reasons for oil being in the cooling reservoir are as following:

  • A damaged or broken cylinder head gasket is often the leading cause for the mixing of oil and coolant in your car. In the situation of any heavy or light damage in the gasket, these two fluids would be allowed to combine.


  • Another reason is probably the damage in the cylinder head. In general, a broken or cracked head of the cylinder would be the result of a serious impact in an accident, overuse of your car or overheating. In this situation, you need to have the cylinder head changed immediately. If it is not performed in due time, the coolant could not be directed properly and eventually get mixed up with oil in the engine.



  • Even though the slight damage in engine block is not common, it can also result in the mixing of coolant and oil as lower part of the engine contains some movable components that use oil.


  • Overuse of your car and overheating is basically not good for most parts of the engine and could lead to different malfunctions, including the combination of coolant and oil that flows into the reservoir. In some extreme situations, the engine might eventually damage head gasket and result in an internal leak of the engine oil as mentioned earlier.


  • Last but not least, excess of water in the engine which rises to the top would be also a reason for the mixing of these two fluids. You car usually passes through water that would come in engine via exhaust pipe to damage the functioning and flow of the engine. As a result, the oil leaks and mix with water.

Solution for Oil in Coolant Reservoir

  • Solution 1: If you open the radiator top or the reservoir and see that the oil-coolant mixture has been generated, and your car has begun to operate in an unusual way, then it is the right time for you to have immediate action. Nevertheless, you could not do anything much apart from cleaning up without specific knowledge on the functioning of the engine. Therefore, it is highly recommended to call a professional car mechanic for a suitable solution to such types of problem.


  • Solution 2: Depending on if the issue is minor or extreme, the mechanic would offer different solutions to your car. For instance, if this is just a small problem, you could simply take care of the engine by cleaning it frequently, changing a couple of components, or correcting several errors in the filter. However, if the problem seems to be serious and last persistently, you might need a comprehensive overhaul of the engine or replacement of soon components to solve the issue.


  • Solution 3: In general, it is really important to handle the mixing of oil and coolant not only because it would lead to the wastage of coolant or oil in the engine, but it could also result in even more serious damage and problem to the car’s engine. Many car experts warn that poor maintenance and use of the vehicle usually tends to put engine system at a substantial possibility of being damaged.


  • Solution 4: When the damage occurs and makes these two fluids mix together, the vehicle’s engine would not work correctly. As a result, you would not be able to drive the car after overuse or overheating. In turn, this might lead to a fire, sparking or even minor explosion in the car’s engine, which would put your life and your vehicle in risks of danger. Therefore, it is really essential to solving this issue as soon as possible.


Oil in coolant reservoir could be a minor leakage result or serious problem, which could be checked in time if you take immediate action.

Since it can become a more serious issue in the future, we highly recommend you to have proper leak tests for the engine performed by a professional mechanic so that the car could avoid severe damages and extend its life.


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12 thoughts on “What Should You Do When Oil in Coolant Reservoir?”

  1. Question – I took my ford f150 to a shop to get a valve job. It was working fine and I noticed that it needed oil. I had to put5 quarts. I then noticed that oil is in the coolant. Do you recommend a good, honest shop?

  2. I discovered oil in my coolant reservoir and I don’t know what to do. The car is fine, no smoke or overheating.
    My concern is the oil on top of the coolant in the resevour.

  3. This information is very useful to me. I experienced this situation today and my mechanic is currently resolving it. He immediately diagnosed the problem after he saw it though.

  4. I discovered a little oil in the expansion tank, but no signs of water in the dipstick, or oil filler cap. When I changed the oil there weren`t any traces of water in the oil. My engine has an oilcooler, where coolant, (not air) cools the oil, so I suspect there must be a leak there, and due to the higer pressure of the oil in relation to the coolant pressure, the coolant never gets into the lubricating system, but the oil gets in the cooling system. It´s been like this for quite a while, and the performance of the engine has never been affected. I replaced the coolant and degreased the tank a few times , and this lasts for several months and thousands of miles. I wonder if this little amount of oil that circulates with the coolant could cause damage to the engine internal passages and jackets?

    • try oil cooler gasket. i replaced the other day when i had oil in coolant reservoir.

      i have mercedes and most german cars have this oil cooler. gasket was £7.

  5. I have a 2001 chevy blazer Xtreme..and I’m getting oil in my radiator…I’ve flushed cooling system water cooling..changed the oil there were no water in oil….installed a new radiator..started vehicle ran it for 20min..turned off and checked the radiator and it looked like chocolate milk

  6. Notice oil in the reservoir of my bmw x3 2007 model but no overheating and the car is working fine. What could be the cause?

  7. I just bought a use SUV Nissan Xterra. I found out that oil in Radiator and reserve tank the color is cream. I keep losing radiator water.

  8. i was driving loss of power oil light came on then batterie light ..pulled over there was oil splashed up aginst fire wall leaking to floor coolant resivouar has signs of oil in it and is empty..!

  9. Hie I have my Dad Cf75 with a paccar engen now the is that it mixers oil and water in the header tank,I have pressure tested the heads and changed the oil cooler but still the problem is still there.kindly help please!


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