Why Is There Transmission Fluid In My Radiator?

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transmission fluid in radiator

If your car’s automatic transmission fluid leaks into the internal radiator tank, it can cause some serious problems. The fluid will mix with the coolant and create a corrosive mixture that can be highly destructive for the engine.

It is important to fix any leaks in the vehicle’s transmission system as soon as possible to prevent this from happening.

This article will discuss the dangers of mixed automatic transmission fluid and coolant and what you can do to avoid them.

Why is coolant getting mixed with the transmission fluid?

oil in coolant

Automatic transmissions usually use transmission oil. A separate fluid passage circulates this oil around the car’s transmission. Transmission fluid passage is different & similarly, coolant passage is different.

So, how come a fluid passes from a different path ends up in the engine’s radiator giving us a contaminated fluid. Following are the leading causes behind the leakage of transmission fluid into the internal radiator tank.

Faulty Transmission Cooler

The leading culprit behind these transmission problems is the transmission fluid cooler. The function of the transmission cooler is to cool down the transmission fluid. Sometimes, these transmission cooler fluids develop leaks that allow them to leak into the radiator.

Bad Seals

Another possible cause of this leakage is a bad seal between the cooling lines and the engine block or radiator itself. If this happens, it will result in transmission oil leaking out into your engine coolant system.

Radiator Cracks

The last potential issue with mixing the transmission and radiator fluids is a crack in the radiator. If this happens, it will allow coolant to leak into the transmission system, which can cause serious damage.

What happens when coolant leaks into the transmission?

Following bad things can happen to your engine when transmission oil leaks into the radiator and gets mixed with coolant.

1. Corrosion and pitting of the metal surfaces.

The coolant and transmission fluid mixture create an acidic environment that can corrode the metal surfaces inside your engine. This can cause pitting, which is a surface defect that can make the metal more susceptible to further corrosion.

Pitting can cause leaks in your transmission system, which may lead to costly repairs. If you notice any signs of rust or corrosion on the metal parts inside your engine, it is best to get them checked out by a professional mechanic before they become worse and more expensive to fix!

If left unchecked, these problems will only continue growing over. If this goes untreated, it can lead to extensive damage and even complete failure of the cooling system. You might need a transmission rebuild after it.

2. Formation of sludge

The acidic mixture can also cause the formation of sludge, which is a thick, gooey substance that can clog up your engine. This will make it difficult for the fluid to circulate properly and lead to overheating.

If you notice that your car is running hotter than usual or an unusual amount of smoke is coming from the exhaust pipe, it may be time for an oil change. If left unchecked, these problems will only continue growing over. If this goes untreated, it can lead to extensive damage and even complete failure of the engine cooling system.

3. Damage to the Water Pump

The water pump is a critical part of the engine cooling system, and it can be damaged if the transmission fluid leaks into the radiator. If this happens, you may have to replace the pump, which can be expensive.

If your car’s water pump starts making strange noises or if it fails completely, take it to a mechanic right away.

4. Damage to the Radiator

The radiator is another critical part of your car’s cooling system. It cools down the engine by circulating water through it and then releasing heat from that water back into the air.

If there are any leaks in this area, you’ll likely need a new radiator before long because they don’t last forever! It will also contaminate transmission fluid. You can prevent these problems by checking your transmission fluid & engine coolant on a regular basis and making sure that it’s not leaking into the radiator.

5. Damaging the Engine

If the transmission fluid leak is left unchecked, it can eventually damage the engine. The acidic mixture will eat away at the metal parts and cause them to fail. It may also lead to a blown head gasket. This is a very expensive problem that can be avoided if caught early enough.

If you notice any signs of corrosion or rust on your engine, get it checked out right away! It’s better to fix these problems sooner rather than later because they will only get worse with time and become more expensive to repair.


This article has discussed the dangers of mixed transmission fluid and engine coolant. We have also provided some tips on how to avoid these problems. Be sure to check your transmission fluid level regularly and fix any leaks in the system as soon as possible!

The best way to prevent transmission fluid from leaking into the radiator is by regularly servicing your vehicle and checking for leaks. If there are any problems with the system, it’s better to have them fixed sooner rather than later because they will only get worse over time and become more expensive repairs. You can also add an additive that helps stop corrosion inside your engine.

How can you avoid engine coolant leaking into your transmission?

There are a few things that you can do to prevent coolant from leaking into your transmission.

Add Fresh Coolant

Make sure the radiator is full of fresh coolant and not mixed with water or other fluids. Plus, the coolant inside the vehicle’s radiator should be at normal temperature and pressure.

Check for an Internal Leak

Check for an internal leak in the cooling line that connects to both sides of the radiator before adding any more coolant. If there is a leak, you will need to repair it first before filling it up again with fresh fluid to prevent further damage from occurring.

Monitor Transmission Fluid Level

It is also important to keep an eye on the level of transmission fluid and make sure that it is not too low. If you notice that the fluid is getting low on the transmission dipstick, you should take your car in for a tune-up so that the mechanic can check for a coolant leak.

By following these tips, you can help prevent coolant from leaking into your transmission and causing further damage to the vehicle.

Frequently Asked Questions

Is coolant and transmission fluid the same thing?

No, they are not the same. Engine coolant is used to keep the engine cool, while transmission fluid helps keep the gears in your car lubricated.

The color of coolant is typically a light green or yellow, while transmission fluid is typically red and has a slightly sweet smell. It should be checked regularly to ensure that it is at its proper level and not leaking out of any hoses or seals. This can prevent your car from overheating, which could lead to a catastrophic engine failure.

How do you flush transmission fluid out of a radiator?

If the transmission fluid leak occurs into the radiator, it will mix with the engine coolant and contaminate the transmission fluid. It will create a thick sludge in the transmission pan that can damage your engine. The only way to fix this is to flush all fluids out of your engine cooling system and replace them with fresh transmission fluid and anti-freeze.

This can be a costly repair, so it’s important to keep an eye on your car’s fluid levels and make sure that the transmission fluid doesn’t leak into the radiator.

If you’re not sure how to flush the fluids out of your system, take your car to a mechanic and have them do it for you. It’s a complicated process, so it’s best to leave it to the professionals.

Can engine coolant mix with the engine oil?

No, they cannot mix. They are two different fluids that serve two different roles in your vehicle’s engine.

The coolant or antifreeze is a mixture of ethylene glycol and water, which helps maintain the engine’s temperature at optimum temperatures as it runs through the cooling system to absorb heat from parts such as the cylinder head and the engine block.

On the other hand, the engine oil serves as a lubricant for moving parts inside your vehicle’s engine to reduce wear and tear. It also forms a seal between these components to prevent air leakage in the combustion chamber, which can affect performance if it is not sealed completely.

How do I know if there is coolant in my transmission fluid?

If you have trouble shifting gears or your vehicle’s gear is slipping, there may be a problem with the transmission fluid.

If the transmission fluid leaks into your car’s radiator and gets mixed with the coolant. You will notice that there is something wrong when you look at your dashboard while driving because it will show that your temperature gauge is on hot and the engine light comes on to indicate that there is some problem with your vehicle.

It can be dangerous because it could cause damage to your car’s engine, which will cost more money in repairs than if you had just fixed the leak before anything else happened. The transmission fluid needs to be replaced as soon as possible.

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