Rear Main Seal Issues
::CF Moderator::
Joined: Aug 2011
Posts: 43,971
Likes: 1,578
From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
CRUISER'S MOSTLY RENIX TIPS
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, 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: “Crap 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. A little tip here. Rather than use a dizzy gasket, use an o ring instead. NAPA #727-2024. Tips 12 and 13 will help you get your distributor back in place correctly.
REAR MAIN SEAL DIAGNOSIS
OCTOBER 31, 2015 SALAD 3 COMMENTSI’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, 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: “Crap 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. A little tip here. Rather than use a dizzy gasket, use an o ring instead. NAPA #727-2024. Tips 12 and 13 will help you get your distributor back in place correctly.
Junior Member
Joined: Jan 2020
Posts: 30
Likes: 6
From: Colorado
Year: 2001
Model: Cherokee (XJ)
Engine: 4.0
::CF Moderator::
Joined: Aug 2011
Posts: 43,971
Likes: 1,578
From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
I don't think I've ever found a 4.0 that the valve cover bolts weren't snug, especially the rearmost ones......
This^^ falls in the "JUST DO IT" category.
This^^ falls in the "JUST DO IT" category.
Member
Joined: Jun 2019
Posts: 190
Likes: 25
From: Greeneville, Tennessee
Year: 1995
Model: Cherokee (XJ)
Engine: 4.0
CRUISER'S MOSTLY RENIX TIPS
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, 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: “Crap 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. A little tip here. Rather than use a dizzy gasket, use an o ring instead. NAPA #727-2024. Tips 12 and 13 will help you get your distributor back in place correctly.
REAR MAIN SEAL DIAGNOSIS
OCTOBER 31, 2015 SALAD 3 COMMENTSI’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, 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: “Crap 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. A little tip here. Rather than use a dizzy gasket, use an o ring instead. NAPA #727-2024. Tips 12 and 13 will help you get your distributor back in place correctly.
Thread Starter
Seasoned Member
Joined: Dec 2019
Posts: 257
Likes: 11
From: Los Angeles
Year: 1992
Model: Cherokee (XJ)
Oil leak found ????
Before starting to replace the rear main seal, I took advice from others on this forum and used the dye test to locate the leak. It seems the oil if leaking from the bolt on the driver side that holds the oil pan over the rear main bearing cap. Is this likely to be only the oil pan leaking or is it the rear main seal? If it's only the oil pan gasket, can I just replace that and leave the rear main seal alone?
Thread Starter
Seasoned Member
Joined: Dec 2019
Posts: 257
Likes: 11
From: Los Angeles
Year: 1992
Model: Cherokee (XJ)
CF Veteran
Joined: Sep 2017
Posts: 1,560
Likes: 307
From: MO
Year: 1996
Model: Cherokee (XJ)
Engine: 4.0
At that mileage, it could last a while longer before leaking but again best to just get it over with while the oil pan is off. Especially if the rear main seal is leaking you'd hate to have the pan gasket done and still have a leak.
Thread Starter
Seasoned Member
Joined: Dec 2019
Posts: 257
Likes: 11
From: Los Angeles
Year: 1992
Model: Cherokee (XJ)
thanks for the advice. I'll do both!
CF Veteran
Joined: Aug 2019
Posts: 1,467
Likes: 267
From: Littleton, CO
Year: '96
Model: Cherokee (XJ)
Engine: 4.0 HO
For my own future knowledge if I ever come across this, can it be visibly obvious if the oil is coming from the rear main or just the oil pan? I'm guessing maybe not if the question was asked... Or are the 2 areas too close together to tell where the oil is coming from even if the area is de-greased and dye is added to the oil?
Thread Starter
Seasoned Member
Joined: Dec 2019
Posts: 257
Likes: 11
From: Los Angeles
Year: 1992
Model: Cherokee (XJ)
For my own future knowledge if I ever come across this, can it be visibly obvious if the oil is coming from the rear main or just the oil pan? I'm guessing maybe not if the question was asked... Or are the 2 areas too close together to tell where the oil is coming from even if the area is de-greased and dye is added to the oil?
CF Veteran
Joined: Sep 2017
Posts: 1,560
Likes: 307
From: MO
Year: 1996
Model: Cherokee (XJ)
Engine: 4.0
Thread Starter
Seasoned Member
Joined: Dec 2019
Posts: 257
Likes: 11
From: Los Angeles
Year: 1992
Model: Cherokee (XJ)
Black pad covering oil pan
This pad is bolted and clipped in. How do I remove the clips and why has this not been covered in any write up or video? Dont even known what this thing is called
Senior Member
Joined: Nov 2016
Posts: 804
Likes: 123
From: Homer Georgia
Year: 2000
Model: Cherokee
Engine: 4.0l