Jeep engine question(blown seal)

genoany · May 30, 2009

My question is my 1994 Jeep cherokee has a blown rear main seal(alot of oil)

The oil light come on periodically. Will changing the seal up the oil pressure or does this indicate permanent engine damage?

The jeep has some pretty rotten floorpans so I do not wish to change the seal unless there is a chance the engine is OK. The repair does not look too difficult, but I have never done one before. If the engine is shot the Jeep goes to the Junk yard(much to the wife"s delight).
Thanks

Mark

Janicholson · May 30, 2009

If the oil is not low, and the light comes on, use thicker oil. The oil pressure is not related to the leak at all (unless there is a leaking cam plug on the rear of the engine) so fixing the two issues separately is necessary. JimN

Anonymous-0 · May 30, 2009

From MY experience with a Jeep 4.0 six, be VERY wary of using thicker oil to increase the oil pressure. In my '88 Jeep Comanche pickup, I decided to "help" the oil pressure by switching to straight SAE-30 high-detergent Havoline motor oil a few years back. After the oil change, the oil pressure was reluctant to pick up enough to turn out the light, and by the time it did [15-30 seconds, according to the lube rack guy at the dealership where I worked] the engine had a rod knocking. The oil pump was shot, and apparently the heavier oil finished it off. Cost me a crank kit, an oil pump, a lower gasket set, and with 60k miles on the odometer, I also replaced the timing chain set [no nylon gears for me, thank you].

So if it was me, based upon my experience with the 4.0, I'd assume the oil pump was on the way out [if you've never replaced one on that engine before], and start looking for a replacement vehicle if you don't want to dig deep to fix this one.

Janicholson · May 31, 2009

I agree for that 6 cyl. Any engine with parts so worn that 30wt oil causes suction problems is in need of primary triage. JimN

Hobo,NC · May 31, 2009

First confirm the PCV valve and plumbing is not stopped up,,, I do not thing the seal has any thang to do with OP

Install a master OP checker gauge to confirm the light operation

I have never had any luck replacing a leak'n rear crank seal on a 4.0 so theirs a no guarantee statement noted and signed on the work order along with prepayment of the attempted replacement of the seal (this is away of run'n folks off with a worn out engine) I do recommend they find a fool that will guarantee his seal will fix the leak

Make sure the leak is not from the front of the engine,,, leaks of any kind will run down the pan rail and seam to B coming from the rear of the engine (BTDT)

Remember NO seal will retain excessive crank case pressure (blow by)

one more thang,,, the head gaskets do leak oil on the 4.0 out the right side of the engine and the oil filter adapter also (if it has a adapter) if the O/F screws directly to the block theirs no adapter,,, if its pointing to the back then their is one

Good engines but a worn out engine is a worn out engine

Rollie NE PA · May 31, 2009

A leaky rear main seal is not uncommon on the older 4.0 Jeeps. My 1992 has been leaking for 3 years now 190,000 miles. I run 20/50 oil in it. Wal-Mart oil. I also have a 1988 with the same leak, 237,000 miles.
Like some one said check the crank case ventilation. Sometimes the vaccuum fitting on the intake will block. The main thing is to keep the oil level full.

Jeep engine question(blown seal)

genoany

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Janicholson

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Anonymous-0

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Janicholson

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Hobo,NC

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Rollie NE PA

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