Signs of a Failing Transmission Cooler

The transmission cooler is a small radiator that cools the automatic transmission fluid that circulates through the transmission. It can be a separate unit, or it may be integrated into the engine radiator.

Hot transmission fluid is pumped from the transmission through a metal line to the cooler, which cools the fluid before returning it to the transmission through another metal line. The transmission cooler allows your transmission to work more efficiently, and the cooling process continues as long as the engine is running.

Does your car have a transmission cooler?

Most vehicles with automatic transmissions have some type of transmission cooler built in. If you have a manual transmission in a normal passenger vehicle that is not exposed to extreme or heavy-duty service, a transmission cooler is not necessary.

To check whether your car has a transmission cooler, contact the service department at the local new car dealer for your vehicle’s brand.

Signs of a bad transmission cooler

Once you have determined whether your car has a transmission cooler, there are several ways to tell if it's going bad. Let’s go through the list:

• Your transmission fluid level is dropping: If you periodically check your car’s fluids (you should), and you notice that your transmission fluid level constantly needs topping up, this could point to a leak in either the transmission cooler or the lines that go in and out of it. Call a mechanic and have the leak fixed. Running out of fluid will quickly destroy your transmission.

• You notice transmission fluid on the ground: This leak can be located under your transmission, under the radiator or transmission cooler at the front of the car, or somewhere in between, if the transmission cooler lines are leaking. Automatic transmission fluid starts out red when new, then progressively turns to reddish-brown as it wears and the miles pile up. It feels oily and slick, and is thinner than your engine oil. It will smell like petroleum. Call your mechanic and have repairs done promptly if you spot a leak.

• You hear odd noises coming from the transmission: Your transmission may have difficulty shifting between gears, or there may be clunking or grinding noises during shifts. This can indicate transmission fluid loss, high internal transmission temperatures, or both, which can be caused by a bad transmission cooler.

• You smell something burning: A bad transmission cooler can cause low transmission fluid levels, which may result in excess friction. The smell of burning transmission fluid is extremely unpleasant, and should send you directly to your mechanic for whatever repairs are needed. .

• Your check engine light comes on: The high internal transmission temperatures from a bad transmission cooler can cause your engine computer to trigger the check engine light on your dashboard.

• Your engine is running hot or overheats: If you are have a bad transmission cooler, the symptoms may spread to your engine, as well. All of that transmission-related heat and drag can make it more difficult for your engine to run properly, and its temperature can also rise as a result. Get to a mechanic right away, and have these issues dealt with.

Should you drive with a bad transmission cooler?

Driving your car with a bad transmission cooler is definitely not recommended. Because you will lose most of your transmission fluid while the car’s transmission is in operation and you are in motion, it is very difficult to know how much fluid you are losing, and at what rate. If you drive your car with insufficient transmission fluid, the risk of serious (and expensive) transmission damage is a real possibility.

How do you fix a bad transmission cooler?

The exact answer to this depends on whether your bad transmission cooler is repairable or not:

If your bad transmission cooler can be repaired, your mechanic can fix the damage and stop the leaks, then reassemble and test the transmission cooler system for proper operation.

If your bad transmission cooler can't be repaired, your mechanic will replace the cooler with a new one, then test the entire system for proper operation. If you have the type of transmission cooler that uses part of your radiator, you may need to replace the entire radiator.

Can you fix a bad transmission cooler yourself?

Unless you have a high level of knowledge of and experience in working on automatic transmissions and their related systems, you should not attempt to repair a bad transmission cooler. You are dealing with a complex system that uses hydraulic-type fluid that is under pressure, as well as major components that you need to access from underneath the car.