Transmission oil coolers are typically installed in radiators. Very few manufacturers offer external coolers, and those are usually limited to their top products. Regardless of the type of cooler, it is vital that transmission fluid be properly cooled. Overheated fluid is the leading cause of transmission failure. Fluid that smells burnt and looks discolored should be replaced and the cooling system checked. If the fluid is milky, this indicates that coolant has migrated from the radiator into the transmission. In this case, the transmission is severely damaged and will have to be removed for repair.
Jack the front of the vehicle up and insert jack stands under the frame. Lower the car onto the jack stands. Place a drain pan under the radiator then open the radiator drain valve under the vehicle and drain the radiator coolant into the pan. Inspect the fluid for discoloration and oily residue floating on top of the coolant. Anything other than clean, uncontaminated coolant is suspect.
Close the drain valve and fill the radiator with fresh water. Start the engine and let it idle for five to 10 minutes, or until it reaches operating temperature. Remove the transmission dipstick while the engine is at idle and check the fluid level. Make sure that the transmission is full of fluid. Allow the engine to idle for another five to 10 minutes, remove the dipstick and check the fluid level. It should be full. If it is low and there are no other transmission leaks, the transmission oil cooler is most likely the problem.
Shut the engine off and allow the vehicle to cool down. Drain the water from the radiator into a clean drain pan. Inspect the water for oily residue. If there is none and the fluid is full, the cooler is in good shape. Refill the radiator with fresh coolant. If there is oily residue, remove the radiator for repair or replacement.
