How Transmission Coolers Work

When things get too hot under heavy loads, transmission coolers will help keep your transmission from overheating.
Joe Belanger/

When you carry small objects, like a book or a bag of groceries, you probably don't notice too much strain. It's easy to carry small things around without breaking a sweat; you might even be able to toss them from one hand to the other. But when the weight of the object increases, the act of carrying becomes more difficult. Carrying a couch or a television, for example, is much harder than carrying a book. Your body will need to work harder and expend more energy to carry the extra weight, and chances are you'll sweat a little in the process.

The same principles apply to our cars. When they're only carrying the driver, cars run easier and use less fuel. If you've packed up your car with every item from your apartment and are moving across town, you might notice the vehicle moving a bit more slowly, and your gas mileage would certainly decrease.


Whether it's our bodies or a car engine, carrying extra weight requires extra energy, and extra energy creates excess heat. The great danger in these situations is overwork and overheating. Too much heat can damage your engine, which can lead to expensive repairs or, even worse, breakdowns on the road. The same is true for your vehicle's transmission.

Tow vehicles carrying thousands of extra pounds of trailer weight do much more work than regular cars and they create lots of heat under the hood. Because of this, many people who tow install transmission coolers into their trucks, SUVs or recreational vehicles. How do they work? Is there one type of transmission cooler, or are there several different kinds to consider? How are they installed?


Choosing Transmission Coolers

Above is a diagram showing a transmission cooler mounted behind a radiator. Choosing the right kind of transmission cooler can make all the difference in your engine's performance.
Automotive Accessories Connection

Transmissions have a lot of work to do: They have to keep your engine's revolutions per minute (RPMs) within a usable range and transmit the power from those rotations to the drive wheels at speeds anywhere from 1 to more than 100 miles per hour (1 to more than 161 kilometers per hour). This generates a lot of heat, and in order to keep this heat low, transmissions rely on a slippery, oily-like substance that lubricates and cools the moving parts.

Sometimes the transmission fluid just isn't enough to keep everything cool. There are times when the fluid temperature can exceed the maximum range of 160 to 200 degrees Fahrenheit (71 to 93 degrees Celsius), and when this happens the fluid begins to burn. This decreases the amount of fluid running through your transmission, which in turn can seriously damage all of the important moving parts within the transmission. The transmission is often one of the most expensive parts of your vehicle to repair, and replacing it is usually the last thing on a vehicle owner's mind.


Installing a transmission cooler is an extra precaution against overheating your transmission, and many people decide to use them in tow vehicles. Transmission coolers come in many different shapes and sizes, and there are a few things to consider when choosing one.

Perhaps the most important factor to consider is the tow vehicle itself. How much does the truck or RV weigh? How much cargo will you be carrying? How much is the trailer weight? Is that the most weight that you expect to carry? Matching a transmission cooler to your vehicle's gross vehicle weight rating (GVWR) is critical to allow this add-on cooler to operate properly. You can investigate all of this yourself online, or you could consult a professional for some (hopefully) solid advice.

Another point to consider is the terrain where you will be doing most of your towing. Will you be towing across long, flat stretches of highway or will you be towing in an urban environment where stop-and-go traffic is the daily routine? What about hilly or even mountainous terrains? Pulling a heavy load up a steep grade can generate a lot of heat in an engine and transmission. Will the transmission cooler be able to cool it down? There's actually quite a bit more to consider than that, but at least now you're thinking of some of the variables that you need to consider when you're choosing a transmission cooler.

So once you've chosen your transmission cooler, how do you go about installing it?


Installing a Transmission Cooler

Where you place your transmission cooler will affect the efficiency of the cooling, so choosing the right spot is important.
Bojan Fatur/

After you've chosen your transmission cooler, it's time to install it. Transmission cooler kits usually come with all the necessary tools, hardware and directions to install it yourself.

First, you'll want to consider exactly where you want to mount your transmission cooler -- there's not exactly a specific spot inside your engine compartment where you're required to place it, so you're given a little room to be creative; however it's still important to place it somewhere where you'll get the most efficiency out of the cooler. If you mount your transmission cooler behind your bumper, for example, there's little chance of it being very efficient since it relies heavily on airflow. Mounting the cooler in front of the radiator and the air conditioning condenser is typically considered the best place. Here, they'll receive a sufficient amount of airflow, yet stay somewhat clear of road debris like rocks.


Transmission coolers are typically square-shaped and thin, so they can easily attach in between other components. Most kits offer adhesive mounting pads that allow you stick the cooler right onto the radiator, but there are also usually extra mounting rods that you can insert between the radiator and the cooler's mounting flanges. You should hook up all of the proper inlet and outlet hoses between the cooler and the transmission -- after all, that's how the transmission cooler delivers the cooled fluid to the transmission. It's also a good idea to make sure you keep the hoses away from any hot or moving parts. Heat would counteract the cooler's effort, and a moving part (like a fan) could sever the line.

For lots more information on transmission coolers and other towing accessories, see the links that follow.


Lots More Information

Related HowStuffWorks Articles

More Great Links


  • "Transmission coolers." (Sept. 22, 2008)
  • Automotive Accessories Connection. "Transmission oil coolers." (Sept. 22, 2008)
  • "Transmission coolers." (Sept. 22, 2008)
  • Transmission Cooler Guide and Installation. "Automatic transmission coolers and engine cooling products." 2008. (Sept. 22, 2008)
  • "Choosing the correct transmission cooler." (Sept. 22, 2008) Category_Code=guide
  • "Transmission coolers." (Sept. 22, 2008)