Automatic transmission cooler lines need to be replaced when they start to leak. These lines connect the transmission to the radiator. As transmission fluid cycles through the engine, it heats up and must pass through the cooler lines into the radiator. In the radiator, the fluid is mixed with coolant and restored to a proper temperature to cycle through the engine again. Replacing the cooler lines on a vehicle requires the transmission to be emptied of fluid so it doesn't come out all over the ground when the lines are removed.
Park the vehicle on a level, firm surface and wait for the engine to cool completely. Raise the front of the car with a jack onto a pair of jack stands to access the underside of the engine more easily.
Slide underneath the engine and locate the transmission drain pan in the center, just off to the driver's side. The drain pan is a large, metal tank surrounded by bolts. Place a drip pan beneath the drain pan.
Remove the drain bolt in the center of the transmission pan with a socket wrench. Attach the socket wrench to an extension tool in order to turn the bolt. Allow 10 to 15 minutes for the fluid to drain completely then replace the drain bolt.
Locate the transmission cooler lines that run from the side of the transmission to the bottom of the radiator. Remove the lines by taking off the nuts with a flare nut wrench. Replace the lines, using the old nuts to attach them to the transmission and radiator.
Lower the car from the jack stands with the jack. Open the hood and locate the transmission dipstick above the drain pan. Pull it out of the metal tube and insert a funnel into the tube. Pour in the required amount of transmission fluid. Replace the dipstick then close the hood.
