Beginning Mechanic's Guide: How To Install An External Transmission Oil Cooler

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The summer heat combined with carrying or pulling heavy loads through mountainous regions can cause your truck transmission to overheat. The extreme heat can damage the internal components in the transmission and lead to expensive repairs. One way to keep the transmission cool is to install an external transmission oil cooler on your truck. This is a job that a beginning mechanic can easily do without much trouble. Here is how to install an external transmission cooler on a truck.

Choosing the Right Size

Transmission oil coolers come in various sizes. You'll want to get the largest one that will fit into the space between the front grille and the radiator and/air conditioning condenser unit inside the front engine compartment area of your truck. Measure the distance from the AC condenser unit, or radiator, and the front of the grille to determine the width of the oil cooler. Then measure the length of the AC condenser or radiator from top to bottom. This will tell you how long the oil cooler can be. Purchase an oil cooler that will fit within the dimensions of those measurements.

Installing the Oil Cooler

A new transmission oil cooler will come with mounting hardware and brackets. Mount the oil cooler to the front frame of the truck. Make sure the hose connections for the cooler are facing in the direction of the transmission.

Find Radiator Hoses

You need to locate the hoses running from the radiator to the transmission. These are normally located on the left-hand side of the transmission. One hose takes the hot oil from the transmission and sends it to a special cooling section inside the radiator. The other hose takes the cooled oil from the radiator back to the transmission.  

If you're not sure which hose is which, here's a test you can do: Disconnect one of the hose lines from the radiator and have someone crank over the truck. If oil flows out of the hose, it's connected to the outlet on the transmission. If no oil comes out, it's connected to the inlet on the transmission.

Connect Hoses to Oil Cooler

You need to cut a length of hose that will stretch from the outlet on the radiator for the transmission oil to the inlet on the oil cooler. You also need to cut another length of hose that runs from the outlet on the oil cooler to the inlet on the transmission. The inlet and outlet will both be marked on the oil cooler.

Connect the hoses to the inlets and the outlets using hose clamps. You will usually need to connect a hose adapter to the outlet neck on the radiator for the hose to the oil cooler to fit properly. The adaptor will usually come with the oil cooler, but if it doesn't, you'll need to buy one that fits into the outlet and has a male end that is the same size as the diameter of the hose you are running from the radiator to the oil cooler.

Test Work

Start the truck and let it run until the engine heats up. Check for leaks around the hose fittings once the truck reaches operating temperatures to make sure everything is working properly before using the truck to carry a load. If you need help, visit a company like