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What Happens When There is Oil in The Coolant Reservoir?

Oil in Coolant

Is your car coolant looking brownish or spotty, even if there’s no rust on the radiator? You might be suffering from mixing of oil in coolant, which is actually a serious issue that needs your immediate attention.

The thing is, oil and coolant should never mix. But, it can sometimes happen, and when it does, it creates a host of serious problems with the car engine.

 To help you understand the situation better and find out how you can fix the problem, here is a complete guide on everything you need to know about the mixing of oil in coolant, starting from what oil and coolant are for, the reasons why these two mixes, and the best solutions you can try.

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What are the functions of oil and coolant?

First, let’s talk about the purpose of oil and coolant in your car.

To put it simply, oil lubricates the movable parts of your car engine so it doesn’t create too much friction when running, while coolant keeps the engine temperature under control to prevent overheating, which is done by regulating the cylinders and combustion chambers in the engine.

You can easily check the color and amount of coolant your engine has by looking under the hood of your car. You should see a plastic reservoir tank that contains orange or green fluid, which is the coolant. There, you can also open the radiator cap to inspect the engine oil.

What’s important to remember here is that your car engine is designed to be sealed so as to protect it from wear and damage. This seal is maintained by the head gasket which prevents oil from getting into the coolant and vice versa.

Important note:

When checking your car’s engine oil, radiator fluid, and coolant, make sure that the engine has cooled down sufficiently, which takes around 30 minutes after the engine has been turned off.

What causes oil and coolant to mix?

What causes oil and coolant to mix?There are actually many other reasons why oil and coolant get mixed up in the engine, the most common being that the head gasket is broken, in which case the coolant may have brownish spots or the oil showcases a milky appearance.

This head gasket can become damaged due to various reasons such as excess heat, over-exhausting the engine, or having not enough oil or coolant. When this happens, the gasket needs to be replaced to prevent oil and coolant from mixing.

Aside from an issue with the head gasket, here are other common reasons why you’re experiencing having oil in coolant:

Damaged cylinder head

Whenever the car engine overheats due to whatever reason, there is always a high chance that the cylinder head may become damaged or cracked. This can also happen when the engine is overused and the car is driven too hard, and of course, when you get into an accident that causes a significant impact to the engine.

A damaged cylinder head can cause a lot of problems, such as leaking oil into the coolant, but if it doesn’t get addressed immediately, at some point, the mixing of oil and coolant may be the least of your concerns.

Damaged engine block

Another probable but less likely issue you might be having that causes oil and coolant to mix is a damaged engine block, which you’ll notice if your car is overheating, releasing blue or gray smoke, or the car isn’t running properly.

Engine blocks are usually damaged when the coolant in the engine freezes up and pushes against the engine’s metal parts. A broken engine block can be fixed through welding, brazing, cold metal stitching, and other methods.

Water in the engine

If you drive your car in rough spots, expose it to heavy rain, water splashes, flood, bodies of water, and the like, water can easily get into the engine, especially through the exhaust pipe and the engine air intake.

The thing is, water, or anything else for that matter, shouldn’t enter the engine, as this will cause a variety of problems that will affect your vehicle’s performance and health, and may even severely damage certain parts.

Other causes

Aside from the ones already mentioned, other possible causes of why oil is leaking into the coolant include improper car servicing at your local shop, and the general wear and tear that happens as the parts and components of your car engine reach the end of their lifespan.

To find out the exact cause of the problem, the best and safest thing that you can do is to take your car to your trusted mechanic for a full inspection, so that problems can be diagnosed accurately and solutions are to be implemented as soon as possible.

What happens when there is oil in the coolant?

What happens when there is oil in the coolant?Now that you know the common reasons why oil and coolant mix in certain situations, you should also clearly understand what happens when oil and coolant mix, so you can have a clear idea of the issues and dangers that this poses.

Having your engine oil mix with the coolant is problematic, and causes a variety of serious problems on your engine’s health and performance. It can significantly damage the engine and result in your car not running properly.

It can also lead to a host of other parts getting damaged and broken, and when worse comes to worst, your vehicle may be prone to electric sparks which can cause fire and explosion, thus endangering your life.

What should you do if there is oil in your coolant?

When oil and coolant mix in the engine, the problems that it creates are not usually readily noticeable, which is why regular servicing is a must. And, if your car isn’t working the way it normally does, this issue should be one of the things you need to check out.

You can check whether there is any oil in your coolant as soon as you feel that something is off in your car. Just pull to the side of the road and stop your car, wait for it to cool down, and look under the hood or remove the radiator cap to check the color and texture of the fluids.

Take it to the shop

If you see any issue, it’s time to bring your car to your mechanic to get the problem diagnosed correctly and get your car engine fixed. You need to be prepared for significant repair costs, especially if your car will require a complete engine overhaul.

And, before you think about it, it’s not a wise idea to postpone any kind of repair, especially when it has to do with your engine. This is because you are only making the issue worse as you continue driving your car with the problems still unresolved.

As such, your engine may continue to malfunction and get damaged even more, leading to more serious issues that will necessitate higher costs in terms of repairs and replacements.

Don’t try to DIY it

You might be tempted to try and fix the problem yourself in order to avoid the exuberant costs that come with taking your car to the local garage, but if you really want to solve the issue and have your car perform normally, don’t do this.

For one thing, don’t just replace the head gasket if you’re not even sure it’s damaged or if it’s the only problem, and don’t try to just pour a liquid head gasket sealer into the radiator without knowing for sure if that is the appropriate solution.

More importantly, don’t go about replacing your engine oil and coolant if you notice that they are mixing. This is largely pointless if the underlying problems that are causing this mixing are not resolved beforehand, and you’ll just be wasting time and money.


When oil mixes with coolant, it’s a serious engine issue that opens doors to bigger and more serious problems that can severely damage your car. To prevent this from happening, make sure to service and maintain your car regularly, and don’t drive your engine too hard.

Even with the best of care, however, oil and coolant mixing can still happen, and when it does, it’s best to resolve the problem quickly, so it doesn’t create more serious problems in the long run, doesn’t run you up thousands of dollars in repair costs, and most importantly, doesn’t lead to situations that can seriously endanger your life and safety.

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One comment

  1. Thanks for the tip that cooling down is an important part to account for before troubleshooting for an engine repair. I plan to find a mechanic soon because with the sound of my car when driving, it seems that it’s been having engine problems. I think it would be best of have a professional mechanic examine it so that finding the cause of the problem would be a lot easier to accomplish.

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