Over time the o-ring between the oil cooler and the housing becomes hardened, flattened, and brittle. All of which can lead to a leaky seal. Luckily the fix is relatively simple.

Note: You do NOT have to drain the coolant to replace this o-ring.

This work was performed on a 1997 Audi A4 1.8T Quattro manual, though the procedures should apply to all 1.8T motors to my knowledge.

The only special tool needed is a 27mm socket to remove the nut holding the cooler in place. I was able to get the nut off with a standard depth socket, though I would recommend using a deep drive to get a better seat on the nut. My socket was just barely able to grab the nut.

The part number for the seal is: 038117070A

Start by locating the oil cooler. If you are facing the car it is located on the right side of the motor under the coolant expansion tank. The oil filter threads onto the oil cooler so if you have done an oil change before you will be working in the same area.

1. Drain the oil and remove the oil filter.




2. Stick your 27mm socket on the nut and break it free. It will spin off the threaded rod. The oil cooler is now free to slide down and off the threaded rod.



This is a view looking up at the housing. You can see the original o-ring stuck to the housing.



Old o-ring.



3. Clean up the contact surface of the oil cooler before snapping the new o-ring into place. The two tabs on the o-ring latch onto the hooks on the oil cooler. Lubricate the o-ring with some oil before putting everything back together to help it seal.



New o-ring in place.



Cleaned up oil cooler secured back into place.



Torque the nut to 18 foot pounds. I had to use an 18" extension to get an angle that would allow my torque wrench to fit (not ideal.)

Install a new (large) oil filter and refill your oil. Enjoy!