Oil in Coolant Reservoir – Causes and Fixes

Finding out oil in Coolant Reservoir can cause you to have a ruined day. In this article, I will explain at length the common causes of oil in Coolant and what you should do to fix this issue. There are different causes of which oil gets into coolant that you should watch out for, hence this article. Do not forget that coolant in oil and antifreeze in Coolant are two different issues that need adequate attention. Hopefully, for the sake of saving hundreds of dollars on replacement costs, I’ll share a trick that I have been using for years. This trick will cost you less than $60.

How do I know if there is oil in my coolant?

how to fix coolant mixing with engine oil

When you remove your radiator or coolant reservoir cover, you should be able to see the color of your antifreeze in the reservoir tank. If there is oil getting into your coolant, you will see residues of oil in the radiator cap. There are different antifreeze colors. Depending on your engine coolant specification, your coolant could be red, green, orange, or pink.

If you remove your coolant reservoir tank and see an oil-like substance,  you probably have oil getting into your coolant somehow. You might ask, what does oil in coolant look like? Suppose you have an oil and coolant mixture; you’ll see a milky color liquid in the reservoir tank. Failure to fix this issue on time will cause catastrophic engine damage.

What causes Oil in Coolant?

Many factors can contribute to this issue. Let’s quickly look at the possible causes.

Leaky Head Gasket: The head gasket is the gasket that sits between the head cylinder and the engine block to prevent coolant and oil from leaking out or mixing. When a car has a blown head gasket, it can cause oil and antifreeze to mix, which could cause this problem. If you have an Overheating engine along with oil residues in the coolant, it could indicate a blown head gasket that needs to be given adequate attention.

You can either take your car to a mechanic garage or get a head gasket tester kit and see if the head gasket is the cause. Suppose the head gasket tester determines that a leaky head gasket is a culprit. In that case, you may have to contact your mechanic to pull off your head cylinder and replace the lousy gasket, or you read on to find out the trick I use to repair a leaky head gasket without pulling off the engine. I do not recommend you try removing the cylinder head yourself unless you’re a certified mechanic.

Oil Cooler: Some cars are designed with oil coolers that help keep the motor oil at optimum operating temperature. If there is a little crack in the oil cooler, it could cause oil and coolant to miss their passing route, resulting in an oil and coolant mixture. This can cause other issues to your cooling system. So, you should fix it once you notice it. If you’re a DIY enthusiast, you can replace the oil cooler. It doesn’t require much technical knowledge.

Overheating: An Overheating engine can degrade your head gasket at a faster pace. Once you have a damaged head gasket, it will indeed cause oil and coolant mixture, which could be the reason for oil in your antifreeze.

Cracked Cylinder head: Suppose you have a cracked cylinder head; it’s going to cause Oil to mix with coolant. The best way to know if you have a cracked head cylinder is to let a mechanic pull out the head cylinder so you can inspect it thoroughly. If you see cracks on the cylinder head, you can either replace your entire engine or replace the head cylinder. Whichever option you choose, it will be cheaper to get a used one from a local dealer and swap it with your own.

Damaged Engine Block: A damaged engine block will cause Oil in Coolant, not the head gasket. This is the least scenario to happen due to how resilient the engine blocks are. If you have a damaged engine block, the best option is to get a new or fairly used engine and have your car running again.

oil in coolant

How to fix oil in coolant

How to fix coolant mixing with engine oil could be a complicated or straightforward fix depending on the problem’s cause. First, you would want to drain out the old contaminated coolant from the radiator petcock or down hose so that you won’t have contaminated antifreeze in your car. Depending on your findings, you would want to face the problem either by repairing or replacing the cause, which could be either a leaky head gasket, cracked head cylinder, oil cooler, or transmission cooler.

Once you have replaced or repaired the cause, you want to refill your coolant tank with the recommended antifreeze. You can consult your owner’s booklet for the right coolant for your car. The next thing you want to do is go for a test run. If you observe any new residues in your reservoir, you want to inspect other possible causes and fix them as well thoroughly. But if there is no sign of oil residues in your coolant, it means you have done an excellent job.

Remember, I promised to show you a trick that I have been using over the years. That said, if you want to know how to remove antifreeze from engine oil or how to stop the oil and coolant mixture, you will find the answer in the next few paragraphs.

If you don’t want to spend hundreds of dollars repairing this fault, you can try using a steel sealant. To use the steel sealant method, you want to make sure that you flush the radiator with a water hose until you see clean water coming out. The clean water shows that you have successfully flushed the contaminated coolant out of your system.

The next thing you want to do is refill your radiator with distilled water and pour a bottle of steel seal or a blue devil. (There are other steel sealants out there, but I recommend these two products). Then, turn on your engine and allow it to idle for about 1hour. You want to make sure you blast your heater and monitor the temperature.

Once the engine has idled for 1 hour, you want to turn off the car and allow it to cool down. After 30 minutes, open the radiator or reservoir cap and inspect for new oil residues. If your coolant is free from oil residues, it means you have done a quick fix. The next thing you want to do is to test-run your car. You have to baby the vehicle for the sealant to have a better chance to do its work.

Unfortunately, some head gasket holes are big enough for the sealant not to work on it. However, it remains the best first option to try out.

Can I use vinegar to flush my radiator?

Vinegar is typically a 5% mild acetic acid. It is excellent to use alone in removing system rust. All you have to do is, add a gallon of distilled water and vinegar and turn on the engine. Allow the engine to idle for about 30 minutes. Remember to blast the heat to enable it to clean your heater core as well. You can use vinegar to flush a clogged radiator.

Can you drive a car with oil in Coolant?

Oil and coolant have different passage routes, and thus, driving a car with oil in coolant but no coolant in oil can cause catastrophic engine damage. This can damage your entire engine leading to costly engine repair or complete engine replacement.

What happens when oil mixes with coolant?

If you notice oil mixes with coolant, you have to find the cause of the problem. Paying no attention to this will cause the motor oil to lose its viscosity and lubricating power resulting in engine Overheating which could lead to a total engine blown over time.

Final word

At this point, I believe this article has answered most of the questions you may have concerning oil in the Coolant Reservoir. We have successfully outlined the symptoms, causes, and how to fix this problem. So, once you notice oil mixes with coolant, you can either try the quick fix method or contact a professional mechanic for a thorough inspection and repair.

Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

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