I have a 96 jeep cherokee sport with 276000ish miles with a growing oil leak. I am assuming it's from the rear main seal based on the oil spot's position and how common it is for the RMS to leak. The question I have is should I replace the front and rear main seal at the same time? My dad (35+ years forklift mechanic experience and generally a whiz at fixing things) said I should due to camshaft wear on the bearings. That makes sense, but I've seen folks replace the rear seal without replacing the front. I don't want to cause another oil leak or some other failure, though. I'd say I'm replacing almost a quart every two weeks with the weather warming up. Next time I change my oil I'd like to try to replace the rear main and oil pan seals. Honestly, should I even bother with those. With 276k miles, should I just wait for the engine to go and worry about everything then? I don't have any knocking sounds and the engine seems to be pretty strong. I just don't know and would appreciate any opinions.

Thanks again!

 

You'll be pulling the oil pan to replace the rear main seal and the oil pan gasket set will incorporate the front seal. There's no 'front main oil seal'


Line up a calibrated foot/pound torque wrench to torque the rear main cap (80 ft/lbs).


You'll need a tube of gray RTV to seal the rear main and the front seal.


Keep track of where the oil pan bolts go.


The two rear bolts are a PITA to get at.


Examine the cylinder walls and piston skirts while you have the pan down. Rotate the crank so you can get a look at each cylinder wall and piston.


See if the oil pump pick up screen is full of crud. Think about replacing the oil pump. Use only a Standard volume pump. Melling makes pumps, and I think the dealer still has them. Requires a new gasket.

 

I can only assume he is referring to the front crank seal. it's easy to do once the timing cover is removed. however, that's a lot of work to change a $3 seal.

 

I generally re-seal the bottom end of the engine all at once - oil pan gasket, rear main seal, front cover gasket, front crank seal, timing chain (if needed), and oil filter housing o-rings. Fel Pro sells a "conversion gasket set" for this job and its pretty cheap. It is more work to tear the front of the engine down, but as CCKen states, the oil pan gasket is part of the front cover seal. If done separately, the front cover gasket set has you cut the oil pan gasket out and replace it with a new (different style) piece. The gaskets & seals are cheap, its the labor that gets you. I usually do this at a coolant change interval & also remove the water pump and replace its gasket & change the thermostat & its gasket and any hoses at the same time. The parts are something like $40 plus the chain if you're doing that too. That way you have a nice leak free engine, fresh coolant, a new chain if needed. I find it easier to clean the entire front of the block when everything is off. Sometimes those front cover gaskets are hard to remove from the block, and having the water pump out of the way makes it a little easier, at at least more complete. Again, its the labor that hurts, not the parts costs. For $40 (or more if you're changing the chain) and a weekend you can have a leak free Jeep, with all fresh gaskets and new coolant

 

I'd do this before proceeding:




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