How to Install a Transmission Cooler

truck work
Trans cooler ready to come out. photo by Matt Wright 2014

If you've done the research and decided that you need a bigger transmission cooler, or your current transmission cooler has sprung a leak, you will need to install a new one. The good news is it's actually a very easy job that can be done in your driveway with regular tools. For some reason whenever we start discussing transmission repair, even seasoned home mechanics start to get a little freaked out. It's understandable considering the inside of an automatic transmission is a very involved place to be. But the cooler install or upgrade (which is also an install, of course) is one of the easier jobs to do on the system. 

What You'll Need:

  • Line wrench or open end wrench set
  • Flat head screwdriver
  • 1/4" drive ratchet set
  • Fluid catch reservoir
  • Transmission fluid

Read on to remove your old transmission cooler and install the new one.

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Remove the Retainer Clips

safety clips
Remove the retainer clips that hold the line nut securely in place. photo by Matt Wright, 2014

Removing the transmission cooler isn't a difficult endeavor on most vehicles. The nice thing about trucks is the fact that most are pretty big, and have lots of room for things like tranny coolers. This means removing and replacing them isn't one of those jobs that requires yoga. 

The steps listed below assume that you have peeled away the layers of your truck that are hiding the transmission cooler location. In most trucks, like our Chevrolet Silverado, you need only remove the grill to access it. 

The first step in removing the cooler is to disconnect the transmission fluid lines at the cooler. There will be two lines connected to the cooler, an input and an output. It doesn't matter which one you disconnect first. The lines are protected from wiggling loose on their own by a plastic retainer that slides over the actual nut holding the line in place. This safety retainer keeps also protects the connection itself. It must be disconnected before you can loosen the line nut on each side of the cooler. They're easy to remove, simply pop them out of the way with a screwdriver.

TIP: It's possible to replace the transmission cooler with very little fluid loss. Careful work will mean little or no fluid refilling before you are able to drive again.

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Disconnect the Transmission Fluid Lines

Transmission fluid line
Disconnect the in and out trans fluid lines using a properly sized wrench. photo by Matt Wright, 2014

 With the safety clips removed, move your catch tray into place somewhere under the transmission cooler. If you have a helper you can have him or her hold the catch tray directly under the cooler to catch every drop of the fluid. If not, don't worry. It's a little bit nasty but not too dangerous. 

Using a line wrench if you have one, or a properly sized open end wrench if you don't, loosen the line nut on the incoming and outgoing transmission fluid lines and pull the lines carefully away. The lines are not super delicate, but take care to avoid crimping them. A crimped line will usually have to be replaced, and that is not a fun job at all. 

TIP: Transmission fluid can harm the plastic and painted finishes on your truck. Protect exposed areas before you disconnect your lines.

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Removing the Transmission Cooler

disconnecting bracket
Remove the small bolts that attach the mounting bracket to the core support. photo by Matt Wright, 2014

With the lines disconnected you are now ready to get the old cooler out of there. The cooler is attached to a bracket, which is attached to your radiator core support. Remove the screws or small bolts attaching the mounting bracket to the core support and you will be able to pull the transmission cooler out. Then you can remove the bracket because you may need it to mount your new cooler, depending on whether you upgraded to a heavy duty transmission cooler or you're simply doing a replacement. 

Installing the new transmission cooler: As the saying goes, installation is the reverse of removal. If possible, pre fill the new cooler so that there will be less air in the transmission fluid system. Once installed and tight, crank up the engine and check for leaks. This also gives a chance for any air pockets to vacate and you can check your fluid level accurately. 

Nice job. You just saved a pile of money!