insane 4.0 oil leakage

background info (bear with me here )

stock 4.0
88 MJ
209k on bottom end
about 1000 miles on rebuilt head

when i bought it it had a cracked valve so was only running on 5 cylinders, was not leaking oil at all. put on rebuilt head runs great now, but noticed some new leakage. tracked it down to the oil filter adapter and the valve cover gasket. redid the gasket with the nice fel pro rubber one, and did the O rings with the mopar factory o rings. no more leaks from the adapter, but after maybe a week it would seem that the valve cover gasket leak came back. so i took it out and cleaned it up and threw it back in and the same thing, good for about a week.
well this past weekend i took it wheeling for the first time, so it got a lot of highway use on the way there. it leaked so bad that it was pouring everywhere and getting on my exhaust to where it was burning it and creating smoke under the vehicle. pulled over to check it out and found that it was seeping through the oil fill cap (its brand new), and the two places where the hoses come out, one to the intake box and one to the manifold. checked the air filter and it was getting soaked with the oil from the valve cover.
now i speculate that the valve cover gasket never was leaking, and that maybe its been leaking from what i just described and just dribbling down towards the back to make it look like it was the gasket.
there is also oil which seems to be from the RMS, but i think this leak could be making it look like its from the RMS but its not. but it could also be both, so I'm not discarding the RMS as a culprit.

now my question is, what could be causing this massive build up of pressure in the valve cover? i know blow by is a possibility, but i don't think thats it since i still have lots of power and don't seem to have lost any compression. I am still working on doing a compression test though to confirm this. but suppose i have good compression and a wet compression test yields little improvement (indicating good rings), what else could be causing this?


oh and for the record i went through 7 quarts on the 3 day trip, i'd say maybe 6-7 hours total spent on the freeway, which is where i lost the most oil.

First off I hope you are using a dyno oil in about the 20W50 range, and not synthetic oil.

It sounds like the vacuum lines may be hooked up wrong on the intake manifold, and air filter and valve cover. The Jeep does not use a PCV valve, but uses a ventilation tube system, with a .5-.8 MM ID tube (and a grommet orifice in the rear valve cover hole) from the rear of the valve cover to the intake manifold. If it is clogged up, or missing, or rerouted by prior owners, it will make the valve cover blow oil into the air filter housing. Also there is breather valve like set up inside the valve cover at the two breather holes that may be clogged up.

I'm running 10w40, do i really need to go to 20w50? seems awfully thick
EDIT: not synthetic

the vacuum lines are hooked up right, i have an 87 XJ to compare it with and mines hooked up exactly the same. i though that the line going to the rear of the valve cover could be plugged too, but i pulled it and blew in it and air flow was fine, so that can't be it. it hasn't been rerouted and goes directly into the intake manifold. sounds like the breather valve(s) might be clogged up? looks like i'll be pulling the valve cover to check and see

Seems that this emulates the same problem I've been chasing for a while. One day no leak, then it just showed up in full force. At highway speeds, it leaks so bad it drips on the exhaust pipe. All indications are it's the rear main, but after cleaning a number of times, still can't locate the cause. Will have to check an see if I've got a similar problem.

Is your air filter soaked in oil? Ecomike has a very good point regarding the CCV lines. Pay attention to that.

Ecomike is probably right on this. Although later 4.0's are better than the earlier on this, the crankcase vent system here seems to rely mostly on black magic or chi or something. It's a delicate balance, and if the lines clog internally, or even, in some cases if they are not the right shape, size and curvature, it will blow out the intake into the filter. ON my old 87 I had terrible blowby problems until I got a new vacuum line from the dealership. It was an upgrade from sharp 90 degree fittings to more gently curved, nothing more, but it solved the problem. It's not at all uncommon for the lines to clog with gunk, and just getting them clear enough to blow through may not be enough to make them work right.

As for the other leak, one of the usual suspects is the O-rings in the oil filter adapter. Owing to air currents and the like, much of this leakage will end up in the same place as leakage from a rear seal, and it can be hard to distinguish sometimes. The O-rings are cheap but the adapter can be hard to get off. Threads on this are common, dealing with the various ways you can undo the ridiculously tight T-60 bolt on the adapter.

cheapcherokee93 said:

I'm running 10w40, do i really need to go to 20w50? seems awfully thick
EDIT: not synthetic

the vacuum lines are hooked up right, i have an 87 XJ to compare it with and mines hooked up exactly the same. i though that the line going to the rear of the valve cover could be plugged too, but i pulled it and blew in it and air flow was fine, so that can't be it. it hasn't been rerouted and goes directly into the intake manifold. sounds like the breather valve(s) might be clogged up? looks like i'll be pulling the valve cover to check and see

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Climate here is normal 35-105 F, Houston, I use 20W50 in all my gas engines, 130,000, 210,000, and 278,000 miles each. They run fine, burn less oil, etc. Bear in mind in the 1970s we all used straight 30 W or 40W oils (not 10W-X or 20W-X).

Check the rear valve cover rubber grommet as well, it has the orifice, and it may be brittle, decayed and trashed into the valve on the inside of the cover. It is more of an oil deflector assy than an actual valve.

If you have too much blow by on the pistons, it will also blow oil into the air filter assy....

Also consider how the CCV plumbing works. If the air filter is clogged up, the intake will suck air from the valve cover, thus drawing in oil!

When all is working properly, air flow is balanced, and air is drawn in from the air filtered side of the filter box, into the valve cover, where it dilutes blow by gasses, and then they are sucked into the intake manifold via the rear CCV line. So look for an air filter problem, clogged Valve cover outlets in the top where the CCV lines attach, clogged CCV line (the rear one), a leaking CCV line (cracked or poor connection, not sealing), and excess blowby into the crankcase. A slight vacuum in the crankcase is critical to keeping oil from getting pushed out of the engine past seals!!!

Just adding to what you said below, even if that small rear CCV is still open, it does not mean it is not partly clogged!!!! A small change in the internal diameter, due to carbon gunk fouling, kinda like gloged arteries, restricts air flow enough to cause the blow by. Just a 30% blockage of the diameter of that tiny line would probably do it!!!

Matthew Currie said:

Ecomike is probably right on this. Although later 4.0's are better than the earlier on this, the crankcase vent system here seems to rely mostly on black magic or chi or something. It's a delicate balance, and if the lines clog internally, or even, in some cases if they are not the right shape, size and curvature, it will blow out the intake into the filter. ON my old 87 I had terrible blowby problems until I got a new vacuum line from the dealership. It was an upgrade from sharp 90 degree fittings to more gently curved, nothing more, but it solved the problem. It's not at all uncommon for the lines to clog with gunk, and just getting them clear enough to blow through may not be enough to make them work right.

As for the other leak, one of the usual suspects is the O-rings in the oil filter adapter. Owing to air currents and the like, much of this leakage will end up in the same place as leakage from a rear seal, and it can be hard to distinguish sometimes. The O-rings are cheap but the adapter can be hard to get off. Threads on this are common, dealing with the various ways you can undo the ridiculously tight T-60 bolt on the adapter.

Click to expand...

wow, thanks for the help! i've been discovering that most of my vacuum lines are brittle, so I'm going to replace them all with new ones from the dealer, including the small CCV one you guys have been talking about. my dad did the same on the 87 XJ and they wernt that expensive so i think new is the best route.

Good choice!!!

Yes. Good choice. And FWIW, in 88 or 89 the size for the orifice might have been changed and the grommet, too. This was to prevent the issue you're describing. Get the rear grommet while you're there..

well i went to the dealer and to my dissapointment they arent making them any more

the parts guy showed me that they have been, and are on back order and that none are even being shipped out anymore. looks like a i may resort to cleaning out the current CCV tube and gromet and finding a somewhat decent vacuum line set in the junkyard.

Try NAPA:

http://www.naxja.org/forum/showthread.php?t=949660

ah, thanks for the info, i will be heading there soon!

got everything at NAPA, it was pretty cheap compared to the dealer. now to put it all in and see what happens

drove to and from class tonight, no sign of new oil on the valve cover and no sign of oil in the new tube going to the air box. looks like that part is fixed, but it still leaks a bunch. that leaves the valve cover (again), distributor gasket, and RMS. already replaced the oil filter O rings and i don't see any leakage there so i know its holding up. i have a feeling its the RMS, which i am really not thrilled about; but I'm gonna try everything to avoid doing it haha

Check that valve real close before jumping on the RMS bandwagon.

I hope you have checked the tightness of the rear oil pan bolts. They can loosen up, and contribute to this.

Matthew Currie said:

I hope you have checked the tightness of the rear oil pan bolts. They can loosen up, and contribute to this.

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Good point. Only takes 5 minutes to do.