Oil leak/Rear Main Seal/Oil Pan Gasket question.

92 XJ
4.5in Lift
32s
Stock gearing.
(Dont know if that is useful)

So this is my second 92. I've come to realize that 70+ mph for long periods of time causes moderate engine oil leakage.

1st XJ had leak. Replaced RMS/Oil Pan Gasket. No more leak. Drive cross country, moderate to severe oil leakage. Never got around to fixing it second time, Sold as is before my move.

2nd XJ (Current) no leaks period. Drive from SF Bay area to Vegas, first gas stop I have that same old oil leak again minor to moderate.

Question: is the rms more likely to be the issue and just failing after long drive at 70+ mph? Or would it be the oil pan gasket blowing out?

It always leaks from back of the engine where engine and trans meet. Yes I know it's engine oil.

I'm still in Vegas and figured I'd see if it is common for one or the other to go bad when driving long periods of 70+ mph.

Thanks!

Too many rear main seals are replaced when the leak is actually coming from the valve cover or the oil filter adaptor.
Any oil leak will migrate rearward toward the bottom of the engine, gravity and the cooling fan push it that way, thus every leak looks like a RMS leak.

Clean the engine and track down the real leak before taking the oil pan off.
Changing the RMS is crummy job, changing the valve cover gasket is easy, in comparison.

About half the time when I spring a leak it is because something is plugged up in the CCV. Even if the leak doesn't stop it may become a drip instead of a constant seep. Pay special attention to the small vacuum line connected to the rear of the valve cover. Make sure the line *and* the connections on both ends are open.

Ok, I just replaced the valve cover gasket a few weeks ago with the higher quality fancy blue gasket lol, it's not coming from the valve cover, I'll check the adaptor and the ccv when I get a chance and let you both know.

Confirmed HG is not leaking? That was one of my leaks before I swapped my HG.

Confirmed HG is not leaking.

As of right now I'm going to say it was a combination of an old brittle RMS, as well as a brittle OPG. The RMS just about broke apart when being removed and the OPG was an old Fel-pro that was cracking and splitting. Replaced them both and no leaks yet. Haven't taken it on a long trip yet either to test it haha.

8Mud said:

About half the time when I spring a leak it is because something is plugged up in the CCV. Even if the leak doesn't stop it may become a drip instead of a constant seep. Pay special attention to the small vacuum line connected to the rear of the valve cover. Make sure the line *and* the connections on both ends are open.

Click to expand...

I don't know if this is an issue here but the rear grommet on my MJ looked fine on top. When I opened it I found this. Not a lot of air going thru this.

The OUTSIDE



And the INSIDE



...and what a NEW one looks like.



When the grommet is cold, there may be some air passing thru the shriveled puffy one, but when it gets hot and soaked in oil there is zero air passing thru it. It is supposed to be open (even if the hose is clear) thru the metered orifice (.26 cm)...the size of the doohickey below is .25 cm.
There's not a lot of room for restriction or error there. Even a small clog can negate the effectiveness of the CCV system.



I purloined this from my doctor's office, it's for looking in ears (.25 cm) for reference.