Hey all, new member here, and new jeep owner as well. I bought a 1990 Jeep Cherokee with the 4.0 engine. It had several problems which I got fixed, and the one remaining was an oil leak. I couldn't tell exactly where it was coming from because it was at the very rear of the engine. After learning a little bit about the 4.0 liter engine's propensity for rear main seal leaks,, knowing where the oil was coming from, and also the amount of oil that is coming out, I convinced myself to replace the rear main. I did that last night, and drove it to work today. The thing still leaks - just as bad as before I replaced the rear main. My question is, what else could it be? There's not too much back there at the rear of the engine. Is it possible I screwed up the install that bad? It didn't seem to be too bad of a job. I did make sure I put the seal in the right direction, so that's not it. Thanks for any help and suggestions. neil

 

I forgot to mention - it has 172k miles on it.

 

valve cover gasket. they are known to leak and they leak in the back so it looks like a rear main

 

oh and welcome to the forum

 

Hi and welcome from Tj in NJ, like a1 said the valve cover or it may even be from the O ring seals in the oil filter housing ( That was my problem) the O ring seals have a tendency to leak and it will drain towards the back of the motor...Tj

 

It's really leaking alot - would the valve cover gasket leak much? I'm thinking it's got to be coming from somewhere that's pressurized. I already replaced the o-ring seals in the oil filter adapter due to some other work that I had to do to it. Thanks, Neil

 

Oh yea it will leak alot from the valve cover. especially on the highway the way the motor sits the oil will go to the back of the valve cover and run down the back of the motor and it will appear to be a rear main.

 

X2 on that, it will leak a lot from the Valve cover...Tj

 

stupid question I know, but you put a new pan gasket in right?

 

when i did mine the gasket was a pain to get on and aligned. it leaked a bit so i took it back off and redid it and it stopped. so yeah that could be as well

 

The 4.0 is a great motor for keeping oil fresh, they are notorious oil leaker's.. When you decide to fix the leaks. ALWAYS, start at the top of the motor and work your way down, fixing as you go. Main culprits are Valve Cover, Oil pressure sender, Oil filter adapter O-rings, oil pan gasket, Rear Main and, rarely, front main seal.

 

wow

 

Thanks for all the replies - I'll check the valve cover gasket next.

Some more info -I did put a new oil pan gasket on when I did the rear main. The one piece rubber type, and had a friend help me with it to make sure I got it aligned right.

Some more info - I bought the jeep for $130 (), and have been spent about $200 fixing up a bunch of little things and getting it road worthy (off-road worthy?), including plugs, wires, distributor, rotor, air filter, oil change, new rear main, and oil pan gasket. In addition, I replaced the o-rings on the oil filter adapter between the block and the filter.

This oil leak is pretty bad, and I really need to get it fixed before moving on to anything else I want to do.

Thanks, again! Neil

 

Since you already replace the rear main seal, the next logical source would be the valve cover gasket. My brothers old girl friend had a Jeep Comanchee with the 4.0L engine and was loosing a quart of oil every 3 days. I work part time in a Sear Auto garage and a few fellow younger weekend mechanics that knew her offered to replace the rear main seal. They did their thing and the truck was still leaking oil. I finally had time to look at the engine and started from the valve cover downward. I noticed a large puddle of oil below the head in a pocket near the engine mount. This could only come from the top some place. I started the engine and could watch the oil pour out of the side of the valve cover. Some other friend of hers, at some replaced the gasket and kinked the rubber gasket ,leaving a small opening between the cover and head.

Take a look at the valve gasket, check the bolts, they loosen up over time and the gasket loses it seal, or if they used RTV, a loose cover will pull the sealant from the mating surface and cause a leak.

If you pull the cover, don't forget to check the PCV valve and clean the openings of dried sludge. The top of the cover does a good job of collecting this sludge over years of ownership.

 

Get under your Truck with a pressure washer or hose and scrub brush

Clean it all off.

Then start your engine and get under the truck and look. If the leak is THAT bad you will see where it is coming from.

More than likely you dicked up the rear main seal on install.

You won't lose a tremendous amount of oil no matter how bad of a valve cover leak you have. Just a few drops while running.

Although I would say it is still a good Idea to change the gasket so you can see how dirty your rockers are.