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Another Rear Main Seal post...quick question


NAXJA Forum User
Hey guys, my rear main seal went tonight, i had a drip every now and then, but man it just spewed a large portion of my oil out tonight. I am almost positive it is the rear main seal but tell me what you think:

I was wheelin with my friend and we were headin back on the highway probably doin around 80 or so with my foot to the floor accelerating (traffic was goin about 80). I started to smell something other then the normal smells and it gets fairly strong. So i turn to my friend and ask him, he says he doesnt smell it, he turns around and tells me to look out the rear window. I could barely see the cars behind me through the smoke. I pulled off the highway and ran to the back and noticed a trail of oil spewed everywhere following from down the highway to a puddle under the front of my jeep and to top it off oil is dripping off my rear diff too. It looks like what happened was it spewed out covering the tranny, crossmember, driveshaft and whole rear axle along with most of my exhaust pipe (causing the cloud of smoke). It was not a pleasant moment in the life of my jeep. I had to get home for a meeting so i called my dad to bring me more oil just in case and filled up with what i had and headed home slowly. The oil pressure stayed around 40 on the ride home and i made it back fine after filling the oil.'

My guess is because i was accelerating hard the pressure built up to the point where the seal finally let loose and once i started taking it easy the pressure was low enough that the seal was holding. Does this make any sense? It didn't leak after that one inicident and i dont even think it is leaking more than a few drops now if even that. Oil is full and only used about a quart and a half after the initial spew. Is there anything else that would fit this description? It seems as if it is coming from rear main because it was dripping all around the bellhousing on the tranny and it definately isnt tranny fluid.
Check along the right side of the block to make sure it's not coming from the oil filter adapter or the oil pressure sender...and don't drive it with an oil-soaked cat and muffler until you clean those off and determine the source of the leak.

I've corresponded with a guy who lost his oil pressure sender on the highway but lost his Jeep shortly after that when the hot exhaust ignited the cloud of oil...
the weird thing about it is that it barely leaks now, maybe one little spot when it has been sitting for a while, like 1 or 2 drops. When i drive it the oil pressure is now up around 55 today. The oil on the cat and muffler burned off on the highway already (thats how i knew i was leaking oil) and they are dry now. I will check those two things though.
It is the rear main seal, and your problem was caused by pressure -- but not by oil pressure.

Your crankcase ventilation system is plugged up. When you put your foot in it, the high revs and heavy load caused more than the normal amount of piston blow-by. This built up pressure in the crankcase and forced the oil out past the seal.

Been there -- done that. (13 quarts of oil from Connecticut to Montana.)
So what do you suggest doing about the crankcase ventilation? I plan on replacing the seal when i get a chance, it isnt giving me problems around town, but i am driving another car now. I have gone harder than that on the thing without problems and this is the first problem.
The 4.0L does not use a PCV valve. The tubes themselves are sized to control the crankcase ventilation. Those CCV tubes are supposed to be replaced every 80,000 miles, when you replace the oxygen sensor.

Replace the CCV tubes. You'll still need to replace the rear main seal, but if you don't replace the CCV tubes you'll blow out a new seal as soon as you put it in.
You could just take the tubes out (the ones stuck in the valve cover) and clean them with solvent and paperclip but youre likely to break them trying to get them out. I had to use a flatbar and pry. Take them to the dealership to get new in the right size (they had serveral?!) and get the o rings also. Once you get them out, coat them with lithium grease and pop em in. I take them off every 15-20k miles to inspect.
Fix the CCV by blowing the lines out with carburettor cleaner or some similar solvent - prefereably from a spray can. On the smaller line, try to work from the small end of the hose first so you can get most of it out.

Once you get everything loosened up, a small flexible wire can help break up anything heavier than the solvent can reach. Work gently, so you don't poke a hole in the line.

Probably won't hurt to clear the hole in the rear grommet - use a small wire or a drill bit (I don't remember what size, but keep it SMALL.)

Since there are oil droplets in the crankcase vapours, they collect and sludge up the lines. Clearing all that stuff out should see to the problem.

At least for the Renix years, NAPA sells the CCV tubing replacement kit (three parts) for about 1/2 to 1/3 of dealer price. The part numbers were posted awhile back (not by me) -- try a search and they should show up.
Here's the link with the dealer part number's:


Found the other one Eagle was talking about. Titled "Why is this happening", 5th reply.

prljeep said:
I disagree (I think)- go to NAPAonline.com I was a disbeliever too!

715-1367 $18.99
715-1366 $18.99 (one is the air filter side, and the other is the valve cover side)
715-1365 $7.69 (This is the little vacuum tube that goes from the intake manifold to the rear of the valve cover. Includes Gromit)

They all come up, just type the number without the dash on the first screen.
They are listed as Belkamp products. Belkamp is a part of NAPA that repackages items made by other manufacturers into a NAPA box.
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Thanks a ton for your help guys, you helped me figure out my brothers oil problems too. But i am still confused on one thing. Take a look at this picture of what i was under the impression was the PCV valve: http://community.webshots.com/photo/269864747/348315055DYyKgM

I looked in the haynes manual which refers to it as a valve, and my brother claims he bought it as a PCV Valve. That picture is the rear of the engine.

The haynes says to shake it to see if it rattles, and if it rattles it is good. I shook my brother's new one, its good, i shook mine, no rattle at all. I think i have bad PCV due to that which caused the pressure that blew my main seal. Does that sound right?
If a pcv valve doesn't rattle, then it is no good. It could be part of the problem.

Not ragging on you, but you need to help us help you. Make sure that we have all the info on the vehicle at the start. Jeep changed things over the years and where my 88 has the tube size controlling the crankcase pressure, your newer one has a pcv valve. Don't think it's even listed in your public profile. Anyways, good luck and have fun.
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That would be an especially neat trick - especially since the 4.0 does not and never did have a PCV valve.

As mentioned previously, the 4.0 uses what is referred to as a CCV - "Constant Crankcase Ventilation" setup. This means that a slight vacuum is ALWAYS present - dependent upon throttle position - at the vavle cover, and that that suction is going to always be venting CC blowby gasses into the intake for another pass at the spark plugs.

The "shake" method of checing a PCV valve is correct, but does not apply to us.

Haynes, by the way, isn't the best writer of tech manuals from what I've seen (I have Haynes, Chiltons, FSM's, and some old Clymer's books lying about. Haynes is usually used to level out odd legs on workbenches around here.)

Do you have a better picture of your part? I'd like to see where the other end of the hose goes, and where exactly the thing mounts. My first impression is of the grommet at the rear of the valve cover where the CCV suction line plugs in - but I've got RENIX, and parts differ.

Meanwhile, cleaning everything out like I mentioned earlier should help with crankcase pressures (pressure will increase due to blowby unless and until it is vented,) and should be fairly simple and cheap. As long as the lines themselves are in good shape, you should just need to clean them and you'll be on your way again. Technically they SHOULD be replaced, but if they're in good condition they can continue to serve (I think mine finally see replacement at around 150-180Kmiles - mainly because the soft rubber parts pull like taffy...)

Sorry i forgot to include info. Its a 1993 XJ with the 4.0 HO. Do you think it is worth it upgrading to the 2000 CCV system?

As far as that picture, that piece connects to a hose going to the intake manifold. When it is connected it is at the rear of the valve cover like where i have been told the rubber grommet is. I will get pics tomorrow if i have time/remember. Thanks.
I'm doing both cause i have the same problem , way too much oil leaking/blowing by in both the air box and out the back end. Just fingured i move that rear hose up to that size , it's about twice the size of the one i have on there almost. So it should last a longer with less chances of blockage like the older style .It's like the if there wasn't a problem with why did they make that rear hose bigger you know. Then i moving below to do do my rear main seal, which i planning on like 2 days min for me , as mine isn't lifted and I've have some back fusion about 5 months ago so i'm giving my self enough time to do the job right.

Mine is a 1993 cheroke country 4.0l HO btw, and my dip is on like the left/driver side of the motor between the oil pan and the trans, which drips onto the exhust and when driveing down the underbody and up onto the rear window , so it's a must do this weekend for me