Oil in Coolant Reservoir – Causes, Symptoms, Treatment

If you’ve been noticing an oil slick in your coolant reservoir, there’s a good chance that your engine is leaking oil. This is a problem that should be fixed as soon as possible, as it can lead to major engine damage if left unchecked. In this blog post, we’ll show you how to diagnose and fix an oil leak in your coolant system. Follow these steps and you’ll have your engine running like new again in no time!

What should you do when there is oil in coolant reservoir? When the two mix, it is a bad occurrence which means that the gasket is not functioning well. This is what creates the internal leakage which, if not taken care of, might damage the engine. It is important that you know what oil and coolant achieve, the causes of oil in coolant, how to test oil in coolant problems, and the solutions for oil in the coolant reservoir.

What Do Coolant and Oil Achieve?​

Oil basically is a lubricant which, when applied, lubricate the various components in the engine which are movable. The parts are the ones which produce a lot of heat due to the generated heat. For it to cool down, you have to use a coolant to ensure that the temperatures of the engine are stable and under control.

In a car, truck or any other vehicle which has four wheels, the engine is normally designed in a peculiar way to make it possible to be covered with a top which could keep foreign elements from the engine.

As your car’s cylinders move, they tend to generate lots of heat. Your car’s cooling system helps to ensure that the engine is cooled down, and this allows for the combustion chambers to be able to operate without having to get hot.

Between the cylinder head and the engine block, there is a head gasket which is important as it maintains the seal between the inside and outside areas of the engine. If there is coolant in your oil, chances are that, you need to replace your head gasket as it is letting the coolant.

The head gasket seal might be damaged or broken due to excess heat due to various reasons including less coolant, less oil, and running the engine with high heats for a very long time.

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How It Works?

  • Two distinct and different channel networks are bored into the engine block of your vehicle. One of the networks is for the coolant while the other is the engine oil. `
  • The network for the engine oil directs the oil to various engine parts where it is required, whereas the same is achieved for coolant or water inside the cooling system of the engine.
  • You can take a look at your engine and you might see the thin line where the head gasket is. You will find it near where you insert the spark plugs.
  • The head gasket ensures that the engine is sealed so that the highest possible compression is achieved and that no leakage of the liquids inside the engine; the coolant and the oil, get into the cylinders.
  • This is possible due to the fact that the head gasket surrounds each cylinder and ensures that it seals them well. The head gasket is constructed from steel but for older vehicles, you might find it constructed from graphite, and can be able to handle pressure and heat of the
  • engine within conditions which are standard.
  • Being a part of the chambers of combustion, the head gasket seems to have the same physical strength requirements and specifications as the other components in the chambers of combustion.

Oil in Coolant Reservoir Causes

The most common causes of oil in coolant reservoir is the fall of the head gasket ​​​​in the engine. But of course, there are other reasons which cause the malfunction to occur. The engine professionals and experts mechanics believes that the following are some of the main causes that will make you experience the malfunction:

  • Broken or damaged cylinder head gasket: This is the leading cause for mixing the coolant and oil in your vehicle. If the damage is light or heavy in the gasket, the two liquids will combine.
  • Damage to the cylinder head: That is the other reason that might cause the malfunction to happen. A cracked or damaged cylinder head would come as a result of a great impact during an accident, overusing the vehicle, or the engine overheating. If that happens, you will need to ensure that the engine head is changed immediately. If you don’t do the change immediately, the coolant will not get to the right destination in the proper way and thus, cause the mixing with the oil in the engine to occur.Engine block damage: Even though it is not a common occurrence, but it might be the cause of the oil in coolant reservoir. It will result in the mixing of the oil and coolant due to the fact that the engine’s lower part contains some movable components which use oil.
  • Overheating and overuse of the car: Most engine parts get affected by overuse and overheating and it could lead to various malfunctions including the mixing of oil and coolant which flows into the reservoir. In situations which are extreme, it might damage the head gasket in the long run and in the process, cause an internal leak of the engine oil.
  • Excess water in the engine: When there is excess water in the engine which rises to the top, it might cause the two liquids mixing. If your car passes through water, it might enter your engine via the exhaust pipe and damage the flow and functioning of the engine. This might result in oil leaks which mix with water.

How To Test Oil In Coolant Problems

There is an easy way to test out if there is oil in the coolant system. The easiest way to ensure that you know if the problem does exist is by putting pressure on the coolant system and find out if it is pouring into the oil pan. For you to be able to test this, you will need to have a pressurized tool for the coolant system.

Steps to follow

  1. You will have to remove the coolant cap
  2. Using the pressure tool, put 1.5 bar pressure
  3. You will have to let it stand for about 10 minutes. If during this time it loses pressure it means that you have a leak on your coolant system which can be either external or internal leak.
  4. You can be able to check for external coolant leaks by having a look under your vehicle.
  5. If there are no external leaks but there is still pressure being lost, you will need to check the oil pan using either the dipstick or tapping out the engine oil to be able to see if you will be able to get any coolant in the engine oil.
  6. If there is an oil cooler fitted on your vehicle, remove it and do an inspection of the gasket, searching for cracks. If it looks dry and old, do a replacement.
  7. Remove the head gasket and check out if there are any damages. If you find no damages or signs of oil mixing between the coolant and the oil channels, then you will need to take your vehicle for a professional check for cracks on the engine block or the head.

Solution for Oil in Coolant Reservoir

  • Solution 1: In case you opened the reservoir or radiator top and find out that the coolant and the oil mixture has been formed, and your car is operating in a manner which is not normal, then it is time that you had an immediate action. But you don’t need to do anything much more other than cleaning up unless you have specific knowledge concerning the functioning of the engine. I would recommend that you call a professional mechanic to give you a solution to such a problem.
  • Solution 2: Depending on whether the issue is extreme or minor, the mechanic will be able to offer various solutions to your vehicle problem. For example, if it is a small problem, you can simply take care of it by ensuring that you clean the engine regularly, changing some few components or correcting various errors in the filter. But if the problem is serious and it seems to last for a longer period of time, you might have to do a comprehensive overhaul of your engine or even replace some components to be able to get rid of the problem.
  • Solution 3: It is very important to ensure that you tackle the problem of mixing of coolant and oil not just because it will lead to oil or coolant wastage in the vehicle engine, but it is possible that it might result in damages which are serious and cause problems with your vehicle engine. Many experts of vehicles warn that, when there are poor maintenance and usage of your vehicle, it might put the system of your engine at a substantial possibility of getting damaged.
  • Solution 4: When there is damage and the two liquids get mixed, it will cause the engine of the vehicle not to work properly. Due to this, you will not be in a position to drive your vehicle after overheating or overusing. In the process, this might lead to sparking, fire, or even an explosion in the engine of your car which might place the life your car and yours in danger. That is the reason why you will need to sort out this issue as soon as possible.

oil in coolant reservoir but car not overheating

Could be a sign of a blown head gasket. A blown head gasket can cause oil to leak from the engine and enter into the coolant system, resulting in excessive oil present in the coolant reservoir. Other symptoms of a blown head gasket include white smoke from exhaust pipe, overheating engine, or coolant leaking externally from the engine block. If your car is displaying any of these signs along with increased oil levels in the coolant reservoir it’s important to have it checked out by an automotive professional as soon as possible. Left unrepaired, a blown head gasket can cause much more serious problems such as engine failure or costly repairs. Have your car inspected and take appropriate action if necessary to avoid further damage to your vehicle.

Is Coolant in Engine Oil Dangerous?

The topic of whether or not coolant in engine oil is dangerous is a hot one. There are those who say that it’s nothing to worry about, and those who say that it can cause all sorts of problems. So, what’s the truth?

Well, the fact is that coolant in engine oil can be dangerous. It can lead to corrosion of the engine, and it can also cause the engine to overheat. If this happens, you could end up with a costly repair bill.

So, if you have coolant in your engine oil, it’s important to get it fixed as soon as possible. You may need to take your car into a mechanic to have the problem fixed.

In the end, it’s always best to be safe than sorry. If you have any concerns about coolant in engine oil, it’s best to get them checked out by a professional.

How Much Will It Cost to Fix Coolant in My Oil?

If you have coolant in your engine oil, it’s important to get it fixed as soon as possible. The cost of fixing this problem will depend on the severity of the issue.

In some cases, the problem may be minor and can be fixed relatively cheaply. However, in other cases, the issue may be more serious and require more expensive repairs.

So, how much will it cost to fix coolant in your oil? This depends on a number of factors, so it’s difficult to give an exact estimate. However, you can expect the cost to be at least several hundred dollars.

Prevention tips to keep your car running smoothly

There are a few simple things you can do to help prevent your car from developing problems. One of these is to keep an eye on the oil level in the coolant reservoir. If you notice that it’s getting low, add more oil as soon as possible. Doing this can help prevent the engine from overheating. Additionally, be sure to keep up with other routine maintenance tasks like changing the air filter and checking the fluid levels. By doing these things, you’ll help keep your car running smoothly for years to come.

Factors to consider before buying oil in coolant reservoir?


The size of the reservoir is an important consideration because you need to make sure that you have enough oil to last for a long time.


You also need to consider the type of oil you need. Not all oils are created equal, so you need to make sure that the oil you choose is compatible with your car’s engine.


Price is always a consideration when making any purchase. You want to make sure that you are getting good value for your money.


When it comes to oil, you don’t want to skimp on quality. Make sure that you get a high-quality oil that will protect your engine and keep it running smoothly.


How often the reservoir will need to be refilled is another important consideration. If you have to refill it often, that can be a hassle. But if the reservoir lasts for a long time between refills, that’s definitely something to consider.

When it comes to buying oil for your car’s coolant reservoir, there are several factors to consider. The size of the reservoir, the type of oil you need, the price, the quality of the oil, and how often the reservoir will need to be refilled are all important things to think about. Make sure you weigh all of these factors before making a decision so you can choose the best oil for your car.

FAQs about Oil in Coolant Reservoir

1. Why Is The Mixing Of These Liquids Harmful For The Engine?

When coolant leaks internally from the intake of cylinder head gasket or manifold gasket, it will end up in two places; burned with an air-fuel mixture which is found in the exhaust or mixed with the oil of the engine. When a coolant mixes with oil, it is bad due to the fact that it forms ethylene glycol, which doesn’t work well as a lubricant.

2. Can You Drive A Car With Oil In The Coolant?

Oil and coolant should never mix and thus, driving a car with oil in the coolant are not advisable as it might just cause serious problems in your engine. This might damage your engine and cause you to have to do expensive replacements of engine parts or the entire engine.

3. What Happens If You Put Engine Oil In The Coolant?

If it happens, the most common cause is normally the head gasket which is faulty. The intake manifold gasket is likely going to leak and allow the coolant to spread down into the crankcase of the engine, thereby mixing with the oil. To check if that is the cause, you will need to remove the intake manifold or the head gasket and then you inspect them for any fault.

4. Can A Bad Water Pump Cause The Oil In Coolant?

Water pumps are not going to cause the oil to enter into the cooling system of the vehicle. Water pumps are designed to allow water to be pumped into the radiator, engine and the heating system. oil coming into water can be caused by:

  • If you have a transmission which is automatic, the fluid of transmission is cooled by the radiator. The radiator might have broken causing the cooling system to have oil. To find out if the radiator has a problem, you can place the dipstick to the transmission and check the oil level. If you find out the oil is milky, then the radiator could be the problem.
  • Oil can mix with coolant through the timing cover. There might be corrosion on the cover which could have eaten through the gallery of the water pump. This will make the coolant to mix with the oil.
  • The head gasket is blown can be another cause. But if that is the case, the engine is likely going to overheat and lose power.check the water in the radiator, the engine oil, and the transmission oil.

5. Why is there oil in my coolant reservoir?

There are a few possible reasons why there might be oil in your coolant reservoir. One possibility is that there is an engine oil leak, and the oil is seeping into the cooling system. Another possibility is that the engine has developed a coolant leak, and the leaking coolant is mixing with the engine oil. If you suspect that there is a problem with your engine’s cooling system, it’s best to have it inspected by a qualified mechanic.

6. Why is there oil in my coolant but no coolant in oil reservoir??

One possible reason for this is that your engine has a coolant leak. The leaking coolant is mixing with the engine oil, and the oil is ending up in the coolant reservoir. Another possibility is that there is an engine oil leak, and the oil is seeping into the cooling system. If you’re not sure what’s causing the oil and coolant to mix, it’s best to have your vehicle inspected by a qualified mechanic.

7. How do I get rid of oil in my coolant system?

If you have oil in your coolant system, the best thing to do is to have it inspected by a qualified mechanic. There could be a problem with the engine’s cooling system, and it’s important to get it fixed before it causes any damage.

8. Can a bad water pump cause oil in coolant?

A bad water pump can cause oil in the coolant, but it’s not the only possible cause. There could be a problem with the engine’s cooling system, or there might be an engine oil leak. If you’re not sure what’s causing the oil and coolant to mix, it’s best to have your vehicle inspected by a qualified mechanic.

Conclusion oil in coolant reservoir

The mixing of the engine oil and the coolant might cause damages which are severe to your car engine, thereby leading to serious problems. But if you are the type of car owner who does the regular maintenance of your vehicle, you might just avoid this. Poor maintenance and use of your vehicle is a factor that might just place your car engine at risk of being damaged.

In case there is damage as a result of fluids mixing up, it will cause the engine not to function well. At times fire, sparking or even a minor explosion in the vehicle engine might occur, putting your vehicle and your life in danger.

The oil in coolant reservoir might be a big issue but if you get it on time, you will be able to save yourself money and time. I highly advise that you get a professional mechanic to be able to handle the inspection of your engine in case you know or suspect a problem. This might just save you from major issues and ensure that you drive with more assurance that your engine is okay.

As you can see, it’s important to keep an eye on your coolant and oil levels. If you notice either of these fluids are low, be sure to top them off as soon as possible. Not only will this help keep your car running smoothly, but it could also prevent a more serious issue down the road. Have you ever had to deal with low oil or coolant levels in your vehicle? What did you do?

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