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.

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.

John Henry

I am John Henry and I have begun to work in automotive industry since the 90s, specializing in car rebuilding and repair. After nearly two decades of working in this complex section, with extensive experience in repairing, troubleshooting and maintaining thousands of cars, I started to work as an auto blogger to share my practical knowledge as well as skills with car owners all around the world through a wide range of articles in online magazine.

Click Here to Leave a Comment Below 12 comments