I think my oil leak woes are finally over...

If you search some of my past threads, you'll see that I have had a pretty bad oil leak on my 99 XJ for some time now. It would only be a big problem on long road trips or when pushing the engine really hard (like in the mountains on the way to the ski resort) and the oil would be dripping out quickly. A few weeks ago I decided to replace the oil pan gasket, valve cover gasket, and the rear main seal. I did all that and I would still have drips on the new cardboard that I park over at night. I finally got the correct tool to replace the oil filter adapter O-rings...

After replacing them, it has now been a week without a single drop of oil on the new cardboard. Needless to say, I am ecstatic.

I was reading an article in Jp magazine last week about how the 4.0 Jeeps are known for "leaving their mark." In the article it mentioned the 3 most common causes for oil leaks, (and I am recalling this from memory since I don't have the mag in front of me), and it said they were: 1) the rear main seal, 2) the oil pan gasket, and 3) the harmonic balancer seal.

I agree with the first two, but has anyone ever had a problem with their harmonic balancer seal? That was the very first time I had even heard of this, so I hope I'm not alone in finding this strange. I am praying that the oil leak I had doesn't reappear only to find out that I gotta change that bugger. It didn't appear to be nearly as easy as the others.

Let's hear your thoughts about that seal...

Glad to hear your leaks have stopped. :thumbup: I'm planning on doing those same seals myself on my '99 in the very near future. I never get any oil on the ground, but I'm still tired of the engine and pan always being covered in a layer of sludge.

I too read that same article you mentioned and was wondering the same thing. I've never even heard mention of the harmonic balancer seal here on before and am hoping I don't need to worry about it. Anyone ever had one leak, or was Jp just a little confused?

my '87 xj developed a "drool" right there at about 180k. and with about 190k my '96 started POURING oil out one day about 100 miles from home-seal had hardened and a chunk of the lip just broke off. it's a really fun job to do in a parking lot on a hot day with very few tools. on that topic, a gutted d-cell maglite head makes a lovely seal installer in a pinch.:gee:
it's not bad at all to do at home when you're prepared, provided the balancer and bolt aren't stuck too badly.

I have 5 XJ's and none of them leak, but I can do a rear main in about 2 hours now and oil filter adapter "O" rings in a half an hour. Its part of owning a 4.0, they love to leak.

I always tell new Jeep owners that if their Jeep isn't leaking oil then they better check and make sure there is some in it.

every 4.0 i've owned so far has leaked from the rear main, oil filter adapter, and oil pan gasket at some point. both renix's came with severely leaking valve covers as well.

So... so far only one person has had a problem with their harmonic balancer seal leaking. Does this mean that Jp Magazine was mistaken in saying that was one of the most common areas for a Jeep to leak oil?

well, fwiw, I've got some oil running down from the front of my engine, and suspected as much about the HB seal, is there another leak that could be more common up front? timing cover? that portion of oil pan?

The actual name for the harmonic balancer seal is the front main seal I believe.

I have a definite rear main / pan gasket leak... have the new gaskets on my desk, just haven't gotten around to installing them yet.

kastein said:

The actual name for the harmonic balancer seal is the front main seal I believe.

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Can anyone verify this?

jeeperguy21 said:

Can anyone verify this?

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Wasn't sure where I read it - turns out it was in 5-90's rear main seal replacement howto. http://naxja.org/forum/showthread.php?t=101118

My parts catalog tells me that Chrysler calls them the "SEAL PACKAGE, Crankshaft" (part number 4778 126 - note only 7 digits) and the "SEAL, Oil, Crankshaft Front" (part number 3300 4681). Usually, the Fel-Pro BS40612 is cited as being the best rear main seal to use; I don't know what the best front main seal is.

EDIT: http://www.jeep4x4center.com/jeep-engine-parts/engine4.0L-242-b.htm seems to have a front main seal for sale, don't know how good it is.

jeeperguy21 said:

Can anyone verify this?

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That's how it pulls up at Napa. I've replaced this on both of my Jeeps so far. Also replaced the rear main, valve cover, and oil filter adapter o-rings on both. Now it looks like the 89 MJ is leaking at the head gasket along the passenger side (no pressure there, just the oil galleys.)