Jeep 4.0 Leak w/synthetic

Messages
460
Location
North Carolina
Well...it finally happened to me. I had been running Havoline or Havoline HM in my old (1990) Jeep Comanche. I recently replaced the Havoline HM 10W30 with Havoline Synthetic 5W30. After 400 miles of driving I have developed a nice leak in the rear of the engine. The Jeep never leaked a drop with any prior oil, so I can only assume that the synthetic cleaned a seal and allowed the leak to occur. In defense of Havoline Synthetic, the Jeep has 160,000 miles and it sat with minimal driving for almost 5 years in my Dad's barn. I have been driving it for 1 year with 2 ARx treatments. The engine runs well and I want to keep it running as long as possible. I chose to run the Hav.Syn because I had it on the shelf and because it has been pretty cold here. The engine runs great with this oil (smooth, nice idle, etc.), but now I have this leak. Would you guys suggest.. - Running the sythetic for another 500 miles to see if the leak stops - Replacing immediately with a HM oil Of course the issue might be that a seal has deteriorated beyond the ability of any oil to stop the leak. In that case I might just have to accept the leak stains on the driveway. Thanks for your advice.
 
Messages
9,461
Location
Not Seattle, but close.
How much leaking are you talking about? If it's a small amount, maybe you can live with it. Maybe another round of Auto-Rx treatments, using the directions for dealing with leaky seals? HM oil might fix it, but maybe not. Maybe worth a try. If it's a bad leak, you might just have to replace the seal.
 
Messages
700
Location
USA
What happened is that the high mileage oil swelled up your seals, and the seals have worn because they were swelled-tighter. Now that the high mileage oil is out, the seals went back to the original size and leak because of the worn seals from being swelled. I'll assume it is your rear main seal. I had to replace mine on my Jeep. If you keep using HM oils, your seals will swell back up and seal better. Any oil other than HM would have leaked.
 

NewGuy

Thread starter
Messages
460
Location
North Carolina
I guess I knew that the correct choice was to switch back to HM oil. I just hated to throw away all of that good oil. I will get a new filter and replace it tomorrow morning. I really don't want to spend the $$ to get the seal fixed. This old truck isn't worth much and I just drive it for odd jobs. It is just a pain to see those oil stains on my concrete driveway. I will let you guys know if the HM stops the leak. Thanks for the advice!!
 

NewGuy

Thread starter
Messages
460
Location
North Carolina
The 4.0 is one tough engine!!! adam123...I haven't looked at it real closely, but the lead does appear to be at the rear of the engine. The oil is leaking down from above the drain plug. Forgive my ignorance, but what is the "torex 60" that you referenced? I will call the dealership and see if they have the O-ring kit. Would you happen to have a part # for this kit or will they recognize it by name? thanks for your help.
 
Messages
625
Location
West, Ky.
Just tell them its the Oil filter Mount O-ring kit. And the Torex 60 is a socket type device just like 3/8,/3/4 etc.. Should beable to pick one up at your local Hardware store. Good luck hope thats it.
 
Messages
4,500
Location
Massachusetts
NewGuy, It is most likely that the rear main seal is leaking on your 4.0L. I have changed many on friends Jeeps (I'm in several Jeep clubs) and it isn't a hard thing to do. The seal itself is a two piece that costs around $12+/- and takes(me) around two hours to install. The oil pan will need to be dropped and the rear bearing cap removed to access the seal. The last seal I did was on my best friends XJ Wagoneer (1989) last year and with 200K+ miles, there are no leaks and it runs strong. A competant shop would probably charge you 4 hours labor to install. Depending on where you live (labor rate), it's around a $250 to $350 job, but worth it if it runs well. I own many Jeeps and only run 5W30 in the winter time. I would go back to your HM 10W30. Depending on the summer temps, I even use 10W40 for extra protection out on the trail. Good luck. [Coffee]
 

NewGuy

Thread starter
Messages
460
Location
North Carolina
Zaedock....I have heard that the rear main seal in these older 4.0s are a problem. I might call around and see what the rate would be to get it changed here in NC. The engine runs great and it is a very handy vehicle to have around. I would have to pay more than $300 for another truck, so it is worth considering. I am definitely going to switch back to the HM oil. Thanks for the advice.
 
Messages
742
Location
Lake Anna, VA
Brother's 98 4.0 TJ began leaking a little from the rear main after I switched it to M1 5w-40 at 87K miles. I changed it again with the same 5W-40 and now at 96K it's quit leaking. The area around the drain plug and transmission was a little wet. After cleaning the area up last time it's stayed dry for over 5K now. Knock on wood.
 
Messages
4,500
Location
Massachusetts
NewGuy Member # 5847 Icon 1 posted January 22, 2006 02:05 AM "Zaedock....I have heard that the rear main seal in these older 4.0s are a problem. I might call around and see what the rate would be to get it changed here in NC. The engine runs great and it is a very handy vehicle to have around. I would have to pay more than $300 for another truck, so it is worth considering. I am definitely going to switch back to the HM oil. Thanks for the advice." Well, I don't know if it's a "problem" per say, but the rear main on a 4.0L is pretty common to seep with some miles on her. At least it's an easy fix. In addition to the rear main, I recommend trying to get a one piece rubber oil pan gasket that has the steel grommets built into the bolt holes too. It can't be over-tightened, and will seal better than cork. Plus, I think the cost is the same. Anyway, going back to HM is cool and may save you the trouble. (Quick story) Back in 2000, I blew the 2.5L/AX5 combo in my '92 Wrangler and swapped in a 4.0L/AW4 auto from a beat '87 XJ until my new 2.5L/SM420 combo was done. That engine dripped everywhere, so I tightened the oil pan gasket until it only leaked a lot. Take it easy.
 
Messages
4,887
Location
Lakeville, MN
Jeeps don't leak - they're only marking their territory! [Smile] As others have said, give the HM oil a shot again for a bit and see if that takes care of it. After that, as stated above, look at the rear main seal or the oil filter adaptor seals. Both are very common on that vintage 4.0l. On my 88 Cherokee, I had a leaky valve cover seal that was repaired that took car of its territory marking days!
 

NewGuy

Thread starter
Messages
460
Location
North Carolina
I found the leak today. I cleaned all of the old oil off the bottom of the Jeep using degreaser and a wire brush. Then I tightened up the oil pan. I drove the truck about 5 miles pretty hard. It is definitely leaking around the oil filter mount. Adam123 was correct!!! Thank you... [Cheers!] The problem is that I don't see any fittings for a wrench other than a 5/8" nut in the center. I will buy a Torex 60 and get the Mount-O-Ring kit from the dealership. Hopefully things will be more apparent once I get the filter off. Any further insight or guidance would be appreciated.
 

NewGuy

Thread starter
Messages
460
Location
North Carolina
I reomoved the oil filter mount and took it apart. On the 1990 model it is held on with a 5/8" nut instead of a Torex nut. The o-rings were brittle and flattened out. I guess after 16-17 years and 165,000 miles the o-rings were shot. I replaced them with the kit from the dealership ($14.50 total) and re-installed the oil filter mount. I changed the oil filter and replaced the Havoline synthetic with Castrol GTX HM 5W-30. I cleaned off the previously leaking oil with degreaser and took the Jeep for a long drive. It was definitely the o-rings that was causing the problem. The rear main seal weeps very slightly, but I don't have any spots on the driveway. I have driven it several times without leaking enough oil to wet the oil pan. I believe that I have the problem solved. I am going to stay with Castrol HM oil as the 4.0 seems to run very well with it. Thanks for all of the help. [Cheers!]
 
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