Oil leaks only when engine running

[88 cherokee owner]

I have an 88 jeep cherokee with 180,000 miles. I have an oil leak that only surfaces when the engine is running. it seems to be from the back of the engine. If this helps, the oil drips off the tranny and the oil plug. also, this is a two wheel drive. Any ideas?

[fredjacksonsan]

Based on other posts I've seen here, it sounds like the rear seal.

In this case, there are two scenarios: 1) Seal is mechanically unsound, so will need to be replaced 2) Seal is sound, but either somewhat inflexible due to age or covered in deposits. For this case, I'd try some Auto RX. I've used this myself and it works as advertised. See www.auto-rx.com (Of course there are many products that claim to clean/revitalize your engine and seals, but I have had no experience with them)


Also, welcome to AF! You'll find a lot of good information here.

[88 cherokee owner]

ive heard a lot of people say in some similar situations, it could be a distributor seal/gasket; any truth to that and where is this distributor located?

[fredjacksonsan]

If you look on top of the engine, you'll see that the plug wires run from the right (passenger) side of the engine to a common point - the distributor. In most pushrod engines there is a long shaft that runs from the distributor down to the crankshaft, and there may be a seal that keeps oil from leaking from this area.

[sector95]

Before you start delving into the the rear main seal, take a good look at your valve cover gasket... better yet just go ahead and replace it as it is easy to do and yours has probably far exceeded its useful life. The 4.0l does have a reputation for bum rear seals but try this first. The engine is mounted with a slight rearward tilt and when it's running, the oil flow in the valve area will drain towards the firewall. If the valve cover gasket has deteriorated, chances are the oil is leaking out the back area of the valve cover, running down the back of the block and *appearing* to come from the rear main seal area. While you've got the valve cover off, make sure your CCV system is clean and will flow easily. The CCV is what is used insted of a regular PCV. The rear elbow is the vacuum draw and needs to be clean to allow a good flow; the front is the inlet for filtered air from the airbox. Doing this will help keep the crankcase from overpressurizing due to blow by and creating a potential for additional leaks.

mike'00XJ

[RedneckXJ4x4]

check the PCV valve, my XJ used to be really bad for dripping oil to and it will leak out thru the air box which in turn heads right toward the bottom of the engine

[88 cherokee owner]

ok so this sounds ridiculous, but i fixed it. the leak was pretty substantial, so when my fix worked, i could just shake my head in amazement. i changed my oil again and used the 'high mileage oil' for the change. i also used some of that engine restorer which is supposed to stop blow-by, restore this and that, and possibly restore seals. well, it seems to have worked as i have no more leaks.