Rear main seal is NOT common failure.
Misdiagnosis of the real leaks is the issue.

CRUISER'S MOSTLY RENIX TIPS
REAR MAIN SEAL DIAGNOSIS
OCTOBER 31, 2015 SALAD 3 COMMENTS EDIT

I’d be looking up ABOVE first, and VERIFYING the source of the oil leak YOURSELF.
Everybody, who doesn’t own or have to pay for or perform your vehicle repairs, loves to poke their noggin UNDER the Jeep and come out bearing the false bad news that your RMS is leaking. Many mechanics, friends, and good old Uncle Bob seem to enjoy telling you it’s the rear main seal. Has a catastrophic ring to it, doesn’t it?
A simple leak at the back of the valve cover or other source could produce the same symptoms. You don’t need to be a mechanic to figure this out. If you have good eyesight and a dim flashlight, you’re good to go on your own. Don’t jump on the RMS/oil pan gasket bandwagon right off the bat.
Almost any oil leak on your 4.0 is gonna drip from the RMS area for two simple reasons:
First off, the engine sits nose-up and any oil will run back to the RMS area.
Secondly, the RMS area is also the lowest point on the engine. Simple physics and the old plumber’s adage apply here: “Crap flows downhill”.
Valve cover gasket, oil pressure sending unit, oil filter adapter seals and distributor gasket, in that order, have to be eliminated as possibilities first. A little tip here. Rather than use a dizzy gasket, use an o ring instead. NAPA #727-2024. Tips 12 and 13 will help you get your distributor back in place correctly.

 

All of my MY Rear main seal issues have been fixed by changing the valve cover gasket....
Your Leaks May Vary.

 

You will never find the leak until you de-grease the entire engine top to bottom. There are many fine products but the best in my opinion is one called Purple Power. It absolutely dissolves everything and is water soluble so it can be rinsed off with a hose. Just cover up sensitive stuff like the alternator.


As Wyo stated, in my case the valve cover gasket also was the culprit. Since you changed yours it could also be the timing cover seal or gasket. You may even have to add a dye to the oil and trace it with an ultraviolet light.

 

<snip> I was told you can go 2 ways pull motor or as last time was done remove the tranny and replaced.

What?? The RMS is a 2 piece seal on the 4.0 You drop the pan and then the rear cap.

And.. what the others say about the VC, Distributor, OFA and others that tend to run to the rear and look like the RMS is leaking.

 

Ok I have changed Valve Cover gasket and Oil filter adapter oil rings and the oil pressure swicth is not leaking and distributor gasket is good and it still is leaking some where. Cant find it.

 

As I have several of the 4.0 engines one was really problematic on the valve cover, previous owner had really torqued on it and not only deformed the hole areas, had distorted the whole of it in what I presume to be an attempt to stop the leaks or was just clueless. I spent a goodly amount of effort trying to straighten it.

2. All gaskets are not created equally, I use the blue Felpro and pay attn to the bolt washers as well. Clamp it down with care and pattern the bolts like a head gasket so you get even clamping force.
Your Leaks May Vary.

 

Then, it might be the rear main seal.
Have you double checked what you repaired and degreased the engine?

 

What VC gasket did you use? Cork ones are very easy to overtighten and cause leaks. Cleaning the head to remove ALL TRACES of the old gasket can be difficult at the rear of the head.

Like WYO suggest, the Feltpro Permadry (blue) have "torque limiters" that prevent overtightening. I have one on my '88.

So back to "square 1". Clean everything, especially the rear of the block (as best as you can), then closely monitor for signs of leakage. If you're certain the other areas are not the source of the leak, then RMS it is. Be prepared for a messy job.

 

Agree with all of the above. I take it a step further and schmear a decent amount of Permatex Ultra Black on the valve cover gasket- both sides. It takes a while longer because you are supposed to let it set up for an hour before final torque then cure overnight. In fact I use it with ALL gaskets no matter what. And I never get any more leaks. As nice as it is to have the built-in grommets so you can't over-crush the gasket- it also allows the gasket to shrink- and leak.

 

Others are correct. All leaks end up at the rear main seal. Valve covers, Oil filter adapter (I think there are 3 o-rings that should be replaced). I did the oil pan gasket, there are a few spots for permatex even with the gasket. The rear main seal does not require you to remove anything major. Engine and trans stay put. Getting the oil pan out can be tricky if you haven't added several inches to your suspension. You need to let the axle droop pretty far to get it out. Unbolting the shocks will help. The scariest part is knocking out the RMS itself. You have to give it a good wack and you don't want to damage the surfaces at all. There are a couple of spots for permatex here too. If you just put in the gasket, I believe it will still leak.

 

Well between me and my trusted mechanic we have determined they rear main seal is leaking so I am determining on what to do he thinks with alomost 280,000 miles on its not worth messing with and if I can get 20,000 more thousand out of the jeep and make 300,000 I will be happy with that.

 

It's a messy job but not really all that hard to do. Two piece seal means you don't have to pull the engine or trans. Did mine in my driveway. Worse part was cleaning all the old gasket material off and straightening the pan sealing lip.

DO NOT USE a steel punch to get the upper half seal out. Make sure you follow the installation procedure in the FSM.

 

Since you're open to "band-aid" tricks, I put a vacuum on the crankcase by blocking the fresh air side of the PCV system (the hose that goes from the front of the valve cover to the air cleaner). Of course, under WOT conditions, crankcase pressures can overwhelm the CCV valve (that's what a PCV valve is called when they put it on the 4.0 Jeep engine) and cause excessive crankcase pressures. I use a power brake booster check valve so when the crankcase is under vacuum, the check valve is in blocking mode. If there is more pressure in the crankcase than ambient, the check valve opens, venting pressure. You can read up on it here.

What could this do to help your situation, you ask? Normally, a leaking seal or gasket will drip minute amounts of oil out while driving. With a vacuum on the crankcase, you would be sucking minute amounts of air into the crankcase where oil normally would leak out. An added benefit is that power is harnessed because of the differential in pressure between the top and bottom of the piston -- burn fuel and create pressure on the top of the piston. Put a vacuum on the bottom of the piston and the pressure differential increases. I know Moroso makes a vacuum pump for race engines that does just that (under WOT conditions where there is no usable engine vacuum).

 

I'm trying to understand this concept. On a closed PCV system, at low rpm, the intake manifold vacuum is putting high vacuum on the crankcase. As rpms increase the vacuum goes down and the scavenging is defeated. That is why the other hose is plumbed to the fresh air intake. As rpms increase the velocity of incoming air increases and takes over sucking crankcase gasses. Therefore at all times there is vacuum on the crankcase. Can the crankcase pressure exceed the PCV vacuum? Yes, especially in a worn engine. I once saw a Chrysler 360 that if you removed the valve cover breather you saw puffs of smoke shoot out every time a cylinder fired. I remember a racing system that ran a hose from each valve cover [on a V8] to a header collector. The exhaust velocity increased as rpm rose and sucked the crankcase fumes. The idea was that the negative pressure also helped seal the rings for less blowby. So if the above system has a check valve that opens under pressure, it merely vents to atmosphere. Would it not be better to connect to a vacuum source like the air filter or exhaust flow or a vacuum motor?

 

Fourspeedman, all of your observations are valid. The concept of putting the crankcase under a vacuum has been around for many decades. The method I use would never survive heavy racing. My ZJ 4.0 has 233k miles, so it isn't fresh any more. Perhaps if it were on its last leg, my PCV mod would quickly get overwhelmed. However, I've been running this under 2 different configurations (the picture shown in Post #13 used a vacuum regulator valve instead of the brake booster check valve) with no adverse effects. My oil consumption has dramatically gone down; which is one of the primary reasons I did it to begin with.

 

Mpgmike I am confused. What is the vacuum source? I am no racer, and I have quite a few high mileage engines. I would be interested in anythinmg that helps with crankcase evacuation. But I don't see it. Are you saying that open-to-atmosphere is better than connected to the air intake box? What am I missing?

 

There are 2 PCV ports on the valve cover; the one at the rear connects to the intake manifold vacuum. The one in the front vents to the air cleaner box. Plug the one to the air cleaner box and do absolutely nothing to the other one. The engine's manifold vacuum will be your vacuum source. Of course, I omitted a few components in this explanation to illustrate where the vacuum comes from.

 

So I need to plug the air cleaner pcv line or I need to add the little air cleaner with vacuum pump?

 

Oh Yeah Now I see your methodology, I too was initially confused....... GOT IT!

One question though, rather than the little filter post Check valve, why not just run back to the filter box after installing the Check valve?

 

One question though, rather than the little filter post Check valve, why not just run back to the filter box after installing the Check valve?

I don't have a stock air filter housing.

 

Wow.. I was trying to illustrate a concept, not necessarily the absolute best method of execution of said concept. Since I replaced the factory air cleaner box with a cone filter, AND didn't add a port for the PCV vent to my home-made adapter pipe, I chose to use the mini cone filter. If nothing else, it acts as a wick to keep the oil from dumping on the engine. Under normal driving conditions, the amount of blow-by is small enough to be drawn out by the CCV (PCV) valve into the intake charge, while still maintaining an effective level of vacuum on the crankcase. It would only be under extreme throttle conditions where the manifold vacuum was so low, AND the crankcase pressures caused by blow-by were so high, that the vacuum CCV set-up (my method of execution) would become overwhelmed. Thus in a racing condition where most of the time is spent at or near WOT, this configuration would prove inadequate.

With the vacuum regulator, it restricts flow in one direction to cause a constant vacuum; bleeding (filtered) ambient air to balance the vacuum level. When crankcase pressures become positive -- above atmospheric pressure -- that first method left nowhere for the pressures to flow. Hence, I replaced the vacuum regulator with a power brake booster check valve. Check valves require a minimal amount of pressure to overcome the flap pressure. The brake booster check valve needs very little pressure to open.

What is happening in MY engine, with THIS configuration is under normal driving conditions, the blow-by volume is less than the flow potential offered by the CCV circuit. Hence, there is a vacuum on the crankcase. When I accelerate normally, the relationship between CCV flow and blow-by remain such that there should still be a slight vacuum on the crankcase. When I pounce on the go-fast-pedal, the crankcase pressures can overwhelm the CCV circuit and create a positive pressure in the crankcase. This is when the brake booster check valve opens venting that pressure. As pointed out, it would ideally be vented to the air filter housing (which I no longer have) and be recycled into the intake charge.

I hope this helps.

 

I just went out to the garage & snapped a shot of the latest rendition with the brake booster check valve:

 

Oooooooh, I get it now. I miss-understood. I thought this was supposed to be better than OEM. Rather, it is a good way to solve a specific problem. You know I had the same problem on my daughter's 1995 Firebird Formula. Someone added a K&N filter but the PCV at the airbox was rendered inoperable. This would have been a great way to fix that. I guess for the OP if he wanted to induce a high vacuum to draw the oil leak back in rather than out, a vacuum pump would be good. Of course if it is a gross leak, repair is the only cure.

 

If you decide not to fix it, it might be worth trying HAPCO Pro-Seal. It's a little expensive and you may need to shop around a bit to find a decent price, but it can sometimes work wonders on smaller engine seal leaks.

 

Can you send a picture of the one you got I looked and there all different kinds for that brand need to know which one thank you.I also have put in Lucas stop leak for engine when changing oil out is this like that or can you just put it in at anytime time.Don’t want to overfill it.

 

No, leave it alone. He removed his factory air filter box and needed a way to vent the crankcase. It is a good fix but does not apply to your situation. I can't believe it is leaking again after being fixed two years ago. Something does not add up. We have two 4.0 XJs with 100k and 180k miles. Neither rear seal leaks. But BOTH needed front timing cover seals and valve cover gaskets done.

 

It’s been about 4 years since it was replaced I checked my invoice and last time it was dumped oil fast now it’s just a slow drip but it is the RMS everything else has been changed or fix that it could be.

 

I know that they changed over to the new type seals that are supposed to be far superior than the old rope type. But the old rope type you took a punch and pushed the old seal back up into the seal cavity in the block. That compressed the seal and increased the seal pressure on the crankshaft surface, effectively 'tightening up' the seal. Then you cut a small part of the new seal and pushed that up into the cavity to fill it completely. Then you put a new section in the bearing half and pressed it in as best you could. Some silicone sealer where the bearing half met the block and now you had a better seal than when it was new. The really old rope seals had some asbestos in them so that got deleted eventually. The non-asbestos seals did not last as long. Eventually they changed to the synthetic seals we have today. I think the problem with them is that they tear unlike the old style.

 

Hapco makes a number of products, This is the only one of their products I've used: Pro-Seal 8 oz - Hapco Products

It worked well for me on two vehicles, both just minor leaks so I don't know how well it would work on more serious ones. Worth a try, a lot easier than replacing a seal if it works and not too much cost involved if it doesn't.

 

FKUNC I got some ordered so i will add some when it gets here I am going to start driving it this week again I had to in shop do some maintenance that I couldn't here at home. So maybe next I will get to add it in and see if it works I drive it 160 miles from home and back to here.Thanks for the idea man.

 

I hope it works for you too, let me know so I have more than just my personal experience to draw on.

 

Update we had to change the Rear Main Seal and all in good now just a little bit of oil every so often. Nothing like before mechanic said seal was hard and brittle and looked like it had never been changed out so we are good to get back on the road next week after I get new Tires on it.