At this point, you likely know the differences between motor oil and coolant, so you know that they are two different colors and do not smell similar. When you pull the oil dipstick, you expect to see amber fluid.
So what happens when you see oil in the coolant reservoir? Knowing these two fluids are not supposed to mix should cause alarm.
In this guide, we are going to highlight the reasons the oil and coolant are mixing, and suggest ways you can fix it or if you should consider using an oil stop leak. We also end with some answers to some questions you may have on your mind.
Causes of Oil In Coolant Reservoir
Oil in the coolant reservoir may indicate a blown head gasket. It may also be a bad oil/coolant heat exchanger or an engine block crack. There may be a bad transmission fluid cooler or heat exchanger or an accidental oil spill.
Let’s look closer at these options.
#1. Blown head gasket.
The head gasket is found between the cylinder head and engine block. It’s responsible for keeping the oil and coolant from mixing.
However, when the head gasket fails, you will either get coolant in the oil or oil in the coolant. You may actually see brown sludge sitting in the coolant reservoir when the head gasket fails.
If you let it go, you will start to experience overheating of the engine. If you continue to run the engine, you can experience catastrophic engine damage.
#2. Faulty Oil/Coolant Heat Exchanger.
The oil/coolant heat exchanger is essential to keeping the engine temperature down. Advanced systems are common in high-performance or race cars.
The function of the oil cooler is to cool the oil. When the cooler, however, fails, motor oil may be allowed to enter the cooling system.
#3. Cylinder Head Cracks.
Most of the time, the cylinder head is above the cylinders, giving the combustion chamber a roof.
However, overhead camshaft or overhead valve engines have exhaust and inlet passages, valves, spark plugs, coolant passages, and fuel injectors, all contained within the cylinder head.
The straight engine has one cylinder head that the cylinders share. The V engines have two cylinder heads, one for each cylinder bank.
Either way, if there is damage to the cylinder head it can allow oil to leak into the coolant. There isn’t usually a simple repair fix, and older, higher-mileage vehicles end up in the junkyard.
#4. Engine Block Cracks.
The engine block is exactly the same. It is not something you want to deal with, but it usually is not an issue on low-mileage, recent production vehicles.
As soon as the engine block goes, you will have to replace the motor. For this reason, the majority of these vehicles will be taken straight to the junkyard.
#5. Faulty Transmission Fluid Cooler/Heat Exchanger.
Are you sure you’re looking at oil? The transmission could have a heat exchanger that’s using coolant for temperature control, although that’s not true for all cars. A crack would cause transmission fluid to possibly be in the coolant.
The coolant can also end up in the transmission fluid. Look closely and see what you have.
#6. Oil Added There By Mistake.
Sometimes, human error occurs. As expert mechanics, this isn’t something we personally run into, but it is very much a possibility for the inexperienced.
There is a proper reservoir for the fluid you will be topping off. There is a filler for oil and there is also a filler for coolant. Filling these reservoirs incorrectly can lead to contamination of the systems.
How To Fix Oil In Coolant Reservoir
If you’re feeling adventurous, you can try to fix the problem yourself; sometimes a fix is not that easy and you’ll need a professional. Let’s talk of ways to fix this.
#1. Pressure Test The Coolant System.
The first step is to do a pressure test. You will need a coolant system pressure tester. Most people do not own one, but you can easily rent one from the auto parts store you go to. After you have the tester follow these steps.
- Attach the pressure tester to the radiator on the cap.
- Pump it by hand up to the pressure that is noted on the radiator cap. Typically this will be from 13 – 16 psi.
- Let the car sit for thirty minutes.
- Inspect the cooling system for leaks and read the gauge for pressure differences.
- If you lose pressure without any external leaks, you have fluid leaking internally.
It’s important to remember that you should never open the cooling system while the motor is hot, or you could be burned.
#2. Inspect Where The Coolant Is Leaking From.
When there is an external leak, you can usually track down the source and fix it. There isn’t usually a part that can break that would cause both an external and internal leak though.
Internal leaks are harder to track down. In this situation you usually have to take apart some of the engine to find out what the problem is, something most people are not set up to do in their home garage.
#3. Repair Or Replace The Faulty Part.
If it’s the head gasket, there is a procedure. You will need to install a new gasket, as well as flush the cooling system completely to remove all of the oil. You may also want to inspect the water pump and radiator for evidence of possible damage.
It is possible, because the oil is heavier than coolant, that they could have sustained damage due to the passage of the oil, as well.
If there’s another component that needs to be replaced, now would be a good time to do that. Some individuals choose to replace the entire engine with a used engine or rebuild it after the block has cracked, if there is still adequate life left in the car.
Whatever repair comes, it is going to be expensive. For example, average cost for a head gasket replacement is $1,600 – $2,000 because it is going to be an intense process.
If you are getting a rebuilt engine, you are looking at anything from $2,000 to $6,000 depending on the make of the vehicle you drive.
#4. Flush The System (After the issue is repaired).
Here are some easy steps to follow if you need to perform a coolant flush.
- Let the engine cool down.
- Jack up the front of the car.
- Clean the radiator with a hose and some soap to not allow dirt to get into the system.
- Check the radiator.
- Put a pan under the drain valve for the old coolant to go into.
- Open the drain valve and let the old coolant run out.
- Once it starts dripping, flush it out with water. Fill up with clean water and put the cap on the radiator.
- Run the engine for 15 minutes.
- Let it cool down again and repeat to empty the water.
- Close the drain valve and refill it with coolant.
You should not pour the old coolant down a drain or on the ground. Make sure to recycle old fluids, either through a local drop-off or take it to your auto parts store.
#5. Contact A Professional.
If any of these jobs feel too large, don’t hesitate to ask a mechanic for help. Better to have a professional take a look at the issue rather than to mess it up.
Because the repair can cost quite a bit, getting a second opinion is beneficial. You wouldn’t want to send your car to the junkyard if the fix is easier than you thought.
Can An Oil Stop Leak Additive Fix The Issue?
Head gasket sealers promise to fill tiny holes to restore compression. In certain circumstances, the additives appear to work temporarily, even allowing you to travel several thousand more miles without issues. In other cases, however, they can cause more damage.
If you’re not going to repair and keep the vehicle, repair the vehicle sooner rather than later, and avoid any additives. If you’re planning to get rid of the vehicle and junk it, by all means, use an additive to buy you some time.
Does coolant always mean a blown head gasket?
Not always, but usually. It could also be a cracked cylinder head or engine block. It could be a failed heat exchanger, or you might have mistakenly added some oil to the coolant system.
How do I get the oil out of my coolant system?
First, you’ll need to fix the problem. It might require a repair of a blown head gasket, but you have to fix it first.
After that, you’ll want to flush out the cooling system to get rid of as much of the oil as you can, and then refill it, and get you back on the road.
Why do I have oil in my coolant but no coolant in my oil?
The blown head gasket isn’t always going to allow the coolant to go into your oil, but it is usually going allow the oil to the coolant.
The longer you do not repair your problem, the worse it is going to get. If you do not fix it, then you may end up with coolant in your oil.
Can a bad radiator be the problem causing the oil to be in the coolant reservoir?
No, you won’t have oil in the coolant reservoir due to a radiator problem. An oil in the coolant reservoir problem is usually caused by a blown head gasket.
There are other situations in which you may end up with oil in your coolant, such as a failed heat exchanger, or cracked cylinder head, or failed engine block, but those are complex repairs.
What happens if you drive with coolant in the oil?
If the coolant can’t keep the engine cool down, the engine can overheat. If the engine oil is leaking, it will continue to get lower, and eventually the engine will run without sufficient oil lubrication.
Either way, you are looking at an engine replacement if you keep driving it.
As soon as you see that the oil is in the coolant reservoir, it is time to do something. You do not want to drive your car with oil and coolant mixing, as this could lead to permanent engine failure.
The longer you go without addressing the problem, the more damage you could be forcing the engine to endure. You may also find yourself broken down on the side of the road when the engine overheats.
If you don’t know how to check the system, have a professional check it and perform a pressure test. Sometimes it’s just best to trust a mechanic far more than you’d want to take a chance and fix something you aren’t familiar with.