Oil Leak: Replace Oil Pump Seal

Application: 1988+ W-body ALL

These engines may leak motor oil, sometimes in small quantities, sometimes in larger quantities. The oil appears to be dripping off the rear part of the engine. This oil leak is most often confused as a leaking rear main seal, and has also been confused as a leaking rear valve cover gasket and a leaking oil pan gasket. In most cases, the oil leak is caused by the oil pump drive seal. The oil pump drive is actually a distributor plug, or the lower half of a distributor. Since these engines do not have a distributor, there is a plug there with the equivelent of the lower half of a distributor to drive the oil pump (driven off the camshaft). The O-ring seal becomes hardened to a consistency of brittle plastic and is ineffective. Due to the presence of full oil pressure under that seal, it causes a great deal of oil leakage.

To verify the oil leak is caused by the oil pump drive O-ring, look at the top of the oil pump drive. It is on the engine block, approximately under the throttle body between the intake manifold and transaxle. If there is any oily residue there, then this is the likely cause of the leak.

The GM Service Department charges 2.3 hours to replace the O-ring on the 2.8L and 3.1L engines. This is approximately $100. On the 3.4L DOHC V6, the cylinder heads must be removed to access the oil pump drive, so labor is far greater.

On the 2.8/3.1L engines, this is not a very difficult thing to replace yourself.

Here's what you'll need to get from your GM Parts dealer:

The O-ring from the dealer will be brown-colored. It is a redesigned silicone O-ring. It should last much longer than the old one. If you buy one from Fel-Pro, it will be black, and probably made of the same material as the original. The total cost for both parts will be about $3.

2.8/3.1L instructions

  1. Remove intake hose from air filter box to throttle body by loosening clamps.
  2. Unbolt throttle-body from upper plenum by removing (2) 13mm bolts.
  3. Remove throttle-body (if necessary). I find it easier to remove it due to the throttle body coolant hoses getting in the way, some people can move it out of the way and be fine. Removal of the throttle body requires disconnecting the throttle body linkages and (2) throttle body coolant hoses.
  4. Disconnect both fuel lines from fuel rail using a 15mm open end wrench.
  5. Remove fuel line clamp on bracket by removing (1) 10mm bolt.
  6. Remove fuel line bracket from cylinder head by removing (1) bolt.
  7. Remove oil pump drive clamp by removing (1) bolt.
  8. Remove oil pump drive using whatever tools you find handy. I use a pry bar that makes the job very quick and easy for me. I have only been able to get it out using just this one specific pry bar though. I believe channel locks or large pliers may work too. The oil pump drive pulls straight up.
  9. Remove old O-ring from oil pump drive. I use a small flathead screwdriver and pry on the O-ring until it breaks, and then I just pull it off. It is very hard and brittle, so it should be easy to remove.
  10. Install new O-ring. The new O-ring is stretchy, just work it up from the bottom over the gear.
  11. Reinstall oil pump drive, making sure to align it correctly with the oil pump shaft. If the shaft came out with the oil pump drive earlier, do NOT forget to put it back in!
  12. Reinstall everything previously removed.

Special thanks to mando for pointing out that I needed to put this tip online for those who may have this problem.