Yeah, yeah, all Jeeps mark their spot. If we hear that one more time we're gonna puke. The real truth is, not all Jeeps mark their spot. Only the ones with shoddy maintenance, worn components, and lazy owners mark their spot. And while most tend to attribute that oil-puking-excuse of a saying to older Jeeps, even newer models from the '80-'90s aren't free from inherent sealing troubles.
Case in point: at around 100K-150K miles almost all 2.5L and 4.0L Jeep engines develop a leak at the two-piece rear main seal, the back of the valve cover gasket, the harmonic balancer seal, or any or all of the above. And while the apathetic Jeep owner can simply add engine oil as needed and tell the neighborhood association, "It's not leaking, it's just marking it's spot," the problem can be taken care of in a couple of hours with simple hand tools. So check it out as we put a stop to the oil leaks on our little 2.5L engine. And if you've got a 4.0L, the process will mostly be the same.
The three most common areas...
The three most common areas for oil leaks on a 2.5L or 4.0L are the valve cover gasket, the rear main seal, and the harmonic balancer seal in that order. The valve cover gasket is the easiest, since the valve cover is pretty simple to just pop off. Since our 2.5L was leaking at the harmonic balancer seal, we stripped the fan, accessory drive, and fan shroud for a teardown.
The only way to get the harmonic...
The only way to get the harmonic balancer off the crankshaft without damaging anything is to rent or buy a harmonic balancer puller. The 2.5L engine bay gives you plenty of room in which to work. On a 4.0L you'll need an extension and a wobbly universal joint to clear the radiator. An impact gun works best to keep the engine from spinning as you install/remove the balancer bolt, but applying the E-brake and putting the vehicle in gear usually works in a pinch if you only have hand tools.
Seals and gaskets simply dry...
Seals and gaskets simply dry up, shrink, and crack over time. This is especially true if a vehicle is left sitting for extended periods of time, as was the case with our Wrangler. After a long hibernation, our harmonic balancer seal in the timing chain cover was hard and cracked. We used a seal puller to pop out the old seal without damaging the aluminum cover, but you can use a prybar or even screwdriver if you're very careful.
Unfortunately, when a seal...
Unfortunately, when a seal dries out and gets hard it can wear a groove into the steel surface of whatever it's designed to seal. In this case, check out the shiny divot in the seal surface of this Jeep's balancer. Even with a new seal installed, this would still leak if not taken care of.
Although our rear main seal...
Although our rear main seal was in good shape, the replacement procedure is to remove the rear main bearing cap and thread a wood screw partially into the seal half that's in the block. Yank it out with a pair of pliers, then lube the new seal half with engine oil and slide it back in the bore. It seems daunting, but it always goes easier than we think it should. Replace the other seal half in the bearing cap and then retorque to factory specs. When installing the pan gasket, we only use a dab of RTV at the corners of the pan gasket and where the rubber and cork gaskets meet. Otherwise, we coat both the gasket and mounting surfaces with Permatex Aviation Form-A-Gasket sealant or Edelbrock Gaskacinch. Don't gun down the pan gaskets more than 12lb-ft, or it can crush the gaskets and cause a leak.
We bought this Fel Pro timing...
We bought this Fel Pro timing chain repair kit for our little 2.5L at our local auto parts store. In addition to the timing chain cover gaskets (which we didn't need), the kit included a new balancer seal, which we carefully tapped into the cover using a seal installer. You can use a regular hammer to install the seal if you're careful. The kit also included a steel repair sleeve for our balancer. You coat the balancer seal surface with the included Red Loctite and then carefully tap on the sleeve to create a smooth, unmarred seal surface.
Since we were already this...
Since we were already this deep into the project, we decided to drop the oil pan because it looked as though the front pan seal had started to weep. You can drop the pan in most 2.5L and 4.0L Jeeps without much trouble, although you may need to remove the swaybar on some 4.0L models. Carefully scrape all the old gasket material off the block and pan in preparation for the new gaskets. Note the amount of sludge in our pan, no doubt due to poor maintenance in the past and its long-term storage.