Rear Main

My mother’s 1998 Jeep Grand Cherokee (60 k miles!) has developed an annoying slow drip at the rear main bearing (6 cyl).
Are there any additives that are safe and might slow this? She just had the oil changed, so it’s not a good time to be talking
about high-mileage oil.

Yes there are in fact. Just go to any auto parts store and buy the more expensive products that are designed to swell oil seals. The products work by sort of re-emulsifying the rubber in those types of seals…kind of like brake fluid does but in a more gentle way. They work and work pretty well…but when it starts to leak again? Its time to replace the seal…you dont really get a second shot at this. There are several products dedicated to exactly this issue. Pep Boys usually has several to choose from.


Hate to be the crotchety old guy but here goes… In the old days ALL cars had a slow drip from the rear main seals. We didn’t care. Kept the oil pans from rusting. Crotchety Filter off

Yes, some of the better oil additive products will help the slow drip. If they don’t fix it completely, don’t worry too much about it unless bigger puddles appear. Be sure to check the oil level periodically, though.

What about checking the PCV valve? A plugged PCV which is entirely possible given the very low miles for the age vehicle could pressure up the crankcase and one of the first places a leak can develop with a PCV issue is the rear main seal. It’s easy to check and cheap to replace if needed.

The area around the rear main seal is where oil leaking from other places often collects and drips from. The rear main itself may not be leaking. It could be the valve cover or the oil pressure sending unit or just the pan gasket.

You’ve gotten a lot of great advice here. If the GC were mine, I’d check the PCV (Positive Crankcase Ventilation) valve, since an inability to vent excess pressure due to a plugged PCV valve will tend to push oil past crank seals when the engine is running.

If the PCV valve is okay, try an additive. Honda gave an excellent description of how these work.

If neither attempt works, you might want to consider Mustang’s suggestion; accept it and just monitor your oil level. If it eventually gets too bad, you can always get it changed at that time. Know that oil seepage past the rear main does not do any other damage an engine, only running too low on oil damages an engine.

The oil pressure sender is a very good suggestion also as a steady drip can often mean a leaking sender as it’s tied into the pressure port.

It also seems that oil pressure sender have a tendency to develop leaks in the spring. I suppose it’s a combination of aged plastic and one cold winter too many.

If it is a very slow leak with just some oil on your garage floor, I’d use an old cookie sheet with kitty litter on it

You will notice that most older supermarket parking lots have dark stains in the parking stalls just where the car’s engine sits.

Looks like this one has no PCV valve.

I recall that the Grand Cherokees had an orifice PCV valve. It was just a hard plastic tube toward the rear of the valve cover. And the oil pressure sensor was next to the oil filter midway to the front. An oil leak at the bell housing would likely be the rear main seal or the cam shaft plug. One of the bearing seal additives might take care of the problem.