HOrnbrod Posted January 15, 2008 Share Posted January 15, 2008 WallyWorld had Mobil 1 syn oil on sale, so I picked some up and put it in my motor last oil change for the first time. Not 200 miles into this oil change, my rear main started leaking. I have not had a leak of any kind since I put the stroker in over two years ago! :mad: I let it run it's course until I had 3K miles, then dumped the crap out today and put in a fresh batch of Chevron DELO 400LE 10W-40 with a new big Mobil 1 filter. Hopefully the rear main will seal itself back up, but I'm not holding my breath. I had read everywhere that syn oil can cause leaks to start; IT DOES! :eek: Link to comment Share on other sites More sharing options...
LJRockstar Posted January 15, 2008 Share Posted January 15, 2008 This actually happened because Synthetic oil, while providing FAR superior protection, is much thinner than conventional oil. You may even notice a slight drop in oil pressure. Putting conventional oil back in may stop the rear main from leaking for now, but it is on it's way out, you will be in there soon enough replacing it. :roll: If it is the two piece seal it really isn't that bad of a job to do. Worst part is taking off the oilpan. Link to comment Share on other sites More sharing options...
HOrnbrod Posted January 15, 2008 Author Share Posted January 15, 2008 This actually happened because Synthetic oil, while providing FAR superior protection, is much thinner than conventional oil. You may even notice a slight drop in oil pressure. Putting conventional oil back in may stop the rear main from leaking for now, but it is on it's way out, you will be in there soon enough replacing it. :roll: If it is the two piece seal it really isn't that bad of a job to do. Worst part is taking off the oilpan. Done it before - not fun. :cry: Any job I can eliminate (or postpone) is good. :cheers: Link to comment Share on other sites More sharing options...
Eagle Posted January 15, 2008 Share Posted January 15, 2008 This actually happened because Synthetic oil, while providing FAR superior protection, is much thinner than conventional oil. You may even notice a slight drop in oil pressure. Putting conventional oil back in may stop the rear main from leaking for now, but it is on it's way out, you will be in there soon enough replacing it. :roll: If it is the two piece seal it really isn't that bad of a job to do. Worst part is taking off the oilpan. Synthetic oil isn't thinner than conventional. "Thinness" is viscosity, and synthetic oil actually maintains its viscosity better than conventional oil. The "problem" is that synthetic oils have more and better detergents than conventional oils, so they tend to clean out gunk and deposits that the dinsaur oils leave behind. In the case of old seals, removing the deposits removes the stuff that's been doing the sealing. Once the gunk is gone, it'll take a long while before it builds up enough to close the gap again -- if it ever does. I think you need to bite the bullet and just replace the rear main seal. It's long overdue anyway. Link to comment Share on other sites More sharing options...
jtdesigns Posted January 15, 2008 Share Posted January 15, 2008 has anyone heard you can't use synthetic oil to break in a fresh engine? Link to comment Share on other sites More sharing options...
TNT Posted January 15, 2008 Share Posted January 15, 2008 One of the other things is synthetic oil has a smaller molecular composition when compared to non-synthetic oil. Basicly it can leak out of a smaller hole. R-134 also has a smaller molecular composition when compared to R-12. R-134 can leak threw R-12 hoses and seals. This is why my 89 will have a complete '95 R-134 AC system. The same thing applys to the extended life Mopar coolant. It will find leaks that were never there before. I converted a car and had leaks all over. The heater valve, thermostat housing, around the hose connections and at the seals on the plastic radiator tanks were it attaches to the aluminum core all started to leak within 3 days. I replaced the radiator, eliminated the heater control valve, put new hoses on and replaced the thermostat gasket. I was never able to stop the thermost from seeping no matter what I did... I'll stick with my green coolant and distilled water on my MJ for sure. Link to comment Share on other sites More sharing options...
DirtyComanche Posted January 15, 2008 Share Posted January 15, 2008 Is a rear main seal only supposed to last 2 years? :nuts: Link to comment Share on other sites More sharing options...
TNT Posted January 16, 2008 Share Posted January 16, 2008 has anyone heard you can't use synthetic oil to break in a fresh engine? Yes use regular oil for break in so the parts wear in correctly. The 4.0 that is going into my MJ has 3000 miles on it and has had 2 oil changes with regular oil. I will be using Mobil One 0w-40 oil in it from here on out. I also use Mopar synthetic 75w-140 gear lube in my axles and Amsoil synthetic ATF in my transfer case. For my AW-4 I run Motorcraft Mercon/DexronIII ATF. I use Fleetguard green coolant mixed with distilled water and add some Water Wetter to it. Link to comment Share on other sites More sharing options...
LJRockstar Posted January 16, 2008 Share Posted January 16, 2008 One of the other things is synthetic oil has a smaller molecular composition when compared to non-synthetic oil. Basicly it can leak out of a smaller hole. This is what I was getting at but didn't describe it correctly. Link to comment Share on other sites More sharing options...
HOrnbrod Posted January 16, 2008 Author Share Posted January 16, 2008 Thanks for all the replies guys. Like I originally mentioned, the stroker has never had had syn oil ever until the last oil change. The motor has been in for almost 2-1/2 years, almost 17K miles. Never leaked until the last oil change. Coincidence - I don't think so. I am running the Hesco high-volume oil pump, and my oil gauge basically stays pegged most of the time except at idle. I'll see if the new Chevron DELO oil slows down the leak, but I suspect Eagle is right and I'll prepare to do the RMS. I'm done with synthetics, except for the diff. Oh - and last time I was down at Hesco, they recommended switching to synthetic oil, which was a major reason why I tried it. Link to comment Share on other sites More sharing options...
BLHTAZ Posted January 16, 2008 Share Posted January 16, 2008 Synthetic is definitley the way to go. I have been an AMSOIL user for over 10 years now, and and AMSOIL dealer for 6 years and I use it in everything I own. The only thing that I have not put it in so far is the MJ as it is not a good thing to put in a high mileage engine that has used conventional oil all it's life as it will cause problems with leaks and the "cleaning" ability described above can actually cause oil journals to clog and restrict/block oil flow if there is a sludge build up inside. I am sorry to hear of your bad experience with Mobil 1 hornbrod, but I can assure you that it's not the oils fault. It is a problem with your seal...and yes, I have seen rear mains go in 2-3 years many times. I'm sure you know it, but I'll say it anyway... ;) It is a known problem with 4.0L engines. I have seen many rear mains replaced under warranty with less than a years use :roll: . Link to comment Share on other sites More sharing options...
Tonedef131 Posted January 16, 2008 Share Posted January 16, 2008 I put synthetic in my man-tran because I wanted the very broad viscosity range it offered. It shifts like new now. However I would never bother putting it in the 4-oh, so other than my tranny the rest of the truck gets conventional dino bones. Link to comment Share on other sites More sharing options...
Duner Posted January 16, 2008 Share Posted January 16, 2008 Again so everyone understands: Conventional oil relies on parafins (parafin wax) to provide lubrication (slipperyness) the side effect is sludgey burnt wax buildup in the engine over time - not to bad if you religously change oil and filter every 3k or sooner. Synthetics do not use any organic compounds to make them slippery so they do not build up sludge but the are really good at removing any deposits in your existing high mileage engine especially around the seals. If your engine is in good condition with low miles it should not effect anything. Otherwise if you want the benefits of synthetic with out the issues on the 160k mile engine just add 1 quart of royal purple at every oil change. I can not vouch for all synthetics but royal purple is designed to blend fully with convential oil. Does anyone have a solution for the leaking valve cover seal or do I just continue to replace evey two years as a maintenance item? Link to comment Share on other sites More sharing options...
Pete M Posted January 16, 2008 Share Posted January 16, 2008 Does anyone have a solution for the leaking valve cover seal or do I just continue to replace every two years as a maintenance item? I used a regular ol' cork gasket with a dab of silicone between the gasket and valve cover and have somehow fixed mine. :dunno: Could be dumb luck though. The proper torque is very important. Link to comment Share on other sites More sharing options...
BLHTAZ Posted January 16, 2008 Share Posted January 16, 2008 You need to find a good quality gasket in the aftermarket and do like Pete said. The factory specs are to use nothing but silicone and you can not even get a gasket at the dealer as they are not made for it. Link to comment Share on other sites More sharing options...
Eagle Posted January 16, 2008 Share Posted January 16, 2008 has anyone heard you can't use synthetic oil to break in a fresh engine? Yeah, I've heard that. Don't tell VW, Audi, BMW or Mercedes -- they haven't gotten the memo. Link to comment Share on other sites More sharing options...
HOrnbrod Posted January 17, 2008 Author Share Posted January 17, 2008 Here's an email I received from Lee Hurley, owner of Hesco: Don, I don't have any problem with synthetics, you have to use compatible weight when changing over. 20W/50 is the grade I recommend for the stroker as the piston moves a long way in the bore. It is a common leak with Jeeps and some time is just an over fill that will start the seals to leak. One of the main problems some have is over filling, never fill to the full mark when changing always leave 1/4" down for heat expansion. Remember with this stroke the rods are closer to the oil and will make oil foam if over filled. This will cause oil leaks. Changing the rear seal is not a big job if needed. Lee I may have been guilty of slightly overfilling at oil changes in the past. :cry: So maybe I can't blame the rear main leak entirely on the Mobil 1. Link to comment Share on other sites More sharing options...
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