Oil leak

I have a 88 jeep cherokee 4x4 4.0 replaced the rear main seal and oil pan gasket and valve cover gasket. And it still leakes. Where else could it leak from?

It's usually helpful to use a strong light and look closely.

Another common source is the joint between the oil filter adapter and the engine block -- there are 3 O-rings there that eventually get cooked and no longer seal well.

Is the leak really lightweight oil? If so, check the power steering high pressure hose. When it starts to fail it usually only sprays a fine mist when the steering is cranked all the way to the stop, and that mist tends to collect on the auto trans cooling line making it look like the source of a leak.

But really, clean everything up well, drive around a bit, then look closely starting at the top and front (because the fans will blow anything toward the rear and gravity will pull anything downward) to find the source(s).

Thanks for the advise! I will definitely check those things out.

Precisely why I wrote this:




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, people on Jeep forums who can’t see your Jeep from where they’re at, 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. "$hit 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.

Revised 02-26-2013

I agree with the above...just like every time a temp gauge creeps above normal it must be a head gasket. Seen many Chevy 5.3 rear mains were replaced when real problem was the back of the intake. To determine oil leaks go to the highest point. Just as post above states it will end up at the bottom due to that gravity thing.

The most common places I've found oil leaks is the rear of the valve cover gasket, the front main seal, the oil filter adapter and the RMS.

One PITA is the front seal and the the oil filter adapter often leak onto the pan rim and travel to the rear of the motor. It can fool you.

I good way to check your front seal is to stick your finger behind and as near the center of the harmonic balancer as you can and see what sticks to your fingertip. Fresh oil is likely a leak or seep, old thick oil and grit is less likely to be a concern.

Even a leaky transmission cooler line can fool you. Some oil usually ends up on the bottom of the bell housing. It may not be noticeably red by the time it makes it to the rear of the motor.

I power wash my motor, being careful to avoid the troubles spots, like the TPS and the distributor etc. let it dry and then drive it around for awhile and then do the XJ crawl with a good flashlight and a small mirror. Dabbing around with a folded piece of white paper towel can also be helpful, stuff our eyes may miss on the dark motor show up on a white background vividly.

And you really need to check the rear vacuum line going to the top of the valve cover, The line itself and both ends where it plugs in. That line gets plugged and a tiny oil seep can turn into a gusher quick.

Thanks guys! The front seal seems to be good still. So ill check out the other problem areas.

I just posted this a second ago in another thread but what the heck - hope it helps. Don't waste any more time trying to eyeball where the leak is coming from without doing a UV dye test - a cheap and effective solution.

I purchased the following parts from Advance Auto with a coupon code and online order/pick up in store I saved 30% to boot:

AutoCraft UV Leak Detection Kit
Part No. AC992/UVA-1CS

Interdynamics Oil and Fuel Systems UV Dye (1 oz.)
Part No. 374CS

Put that dye in where you normally pour in the oil, drive it around town. Then park in a garage at night with the lights off, or at night outside will do but try to get somewhere with very little ambient light, use the UV light and glasses to see where that oil is coming from. Sure there are better kits out there but this did the trick for me - which was to show me that I had a constant drip from my rear main seal.

Replaced the oil pan gasket and rear main seal, no more burning oil stink from the leak burning off the oil pan, no more puddles on the driveway

Good luck!