regular mobil 1 10w30 for jeep 4.0?

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Hi guys, Any thoughts on the flat tappet Jeep motor, being sensitive to the newer oils, or is that a thing of the past? Are they more sensitive to synthetics? I know of a few dino oils guys have had good luck with, I'm thinking about just running it on dino and forgetting about it! Any thoughts?
 
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 Originally Posted By: ryan2022
Hi guys, Any thoughts on the flat tappet Jeep motor, being sensitive to the newer oils, or is that a thing of the past? Are they more sensitive to synthetics? I know of a few dino oils guys have had good luck with, I'm thinking about just running it on dino and forgetting about it! Any thoughts?
MANY threads can be found on here about the Jeep 4.0. They're not super hard on oil, and M1 10w30 would be fine. Yes they have flat tappets, but the valve spring pressures are low compared to the muscle car engines that have had lifter problems in recent years. Many people, including myself, like Shell Rotella T Synthetic 5w40 in the 4.0.
 

ryan2022

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Yeah, I've read through a pile of the posts. It still wasnt clear to me. I still cant bring myself to run a deisel oil, but they seem to be a good bet. Thanks for the reply.
 
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Anything works. The sun will run out of hydrogen before your 4.0 dies from lube related stuff. It may or may not tick/click ..even if well cared for or neglected. You may or may not consume oil. It really won't matter much. Use a 5w-20 if you want. Use a 15w-40/50 if you want
 
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I read on one of the Jeep boards a while back the 4.0L Jeep did better with a 10W30 oil than any of the 40wt oils. As I mentioned "I read", seems they had tear downs and UOA's to back it up. FWIW.
 
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 Originally Posted By: ryan2022
I'm thinking about just running it on dino and forgetting about it!
So Mobil 1 or dino? Mobil 1 is not dino. Did you mean Mobil 10w-30 (without the "1")?
 
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Any modern SM, ILSAC GF-4 licenced oil should do great. They test for cam and lifter wear to get this rating. http://www.swri.edu/4org/d08/GasTests/iva.pdf According to Valvoline, Use a break-in oil or additive during break-in only, and then only on high spring pressure, high performance flat tappet engines. Then you can switch to regular SM oil--even on those engines. I don't think you need to worry at all about regular Mobil 1 in your Jeep.
 
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 Originally Posted By: ryan2022
thanks fellas. I think when I said Mobil 1 and dino, its was a separate thought. thanks again.
I forgot you asked if there were any special issues with the 4.0 and synthetic. Short answer: no. The rear main will probably start to weep eventually no matter what you use. Mine seems to put about 1 drop per overnight on floor where I park it, and that was with Pennzoil yellow bottle (jiffy lube default) that the previous owner used, with the fill of Mobil 1 10w30 I ran, and with my current diet of Rotella T Synthetic (which is actually a petroleum-derived Group III+ oil, not a natural gas derived PAO Group IV). Like Gary said, it'll run forever on pretty much anything. I use synthetic HD (diesel) oil because I like the engine to look brand-new clean when I open it up to replace gaskets occasionally, and because I like to push my change interval out beyond 5000 miles consistently. Not because I really need them for wear protection. I will probably see how it does with a fill of M1 0w30 AFE at the end of summer. The 4.0 isn't a gas mileage champ, so I don't really expect much change, but what the heck. VOAs on that oil look pretty good.
 
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 Originally Posted By: demarpaint
I read on one of the Jeep boards a while back the 4.0L Jeep did better with a 10W30 oil than any of the 40wt oils. As I mentioned "I read", seems they had tear downs and UOA's to back it up. FWIW.
Probably so. I imagine that a different group of people could prove the same thing with a 40 grade being the winner. What you would probably find is that the tester (or the test conditions) is the difference in the results ..or not Most 4.0 engines that are degraded are hurt due to moving 40" meats while the owner is looking for an excuse to do a V8 swap so he can upgrade to 44" meats. The most frequent fatigue item I've ever heard of in a 4.0 is the timing chain. At least in what would require attention. Any that have really broken have been hammered. As I said, they may or may not have lifter noise over a wide range of care. Just my opinion based on observations.
 
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 Originally Posted By: Gary Allan
Most 4.0 engines that are degraded are hurt due to moving 40" meats while the owner is looking for an excuse to do a V8 swap so he can upgrade to 44" meats.
Most of the 4.0s I hear about getting seriously hurt have been hydro-locked from trying to cross rivers without a snorkel :-/ And a number of them continued to run with one or more bent rods for a surprisingly long time. I have heard of a few putting rods out the side of the block when subjected to sustained high RPM (even if not technically over-revved). It really doesn't seem to like being spun fast, but then it's got no additional torque above ~4000 anyway so spinning it up there is little more than abuse anyway.
 
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Yeah ...there's a few that got in over their head ..so to speak. Most of the tired engines (4.2's) are those that were 20 some odd years old and in CJ's ..reclaimed for trail use after having a couple of decades as farm/summer camp/snow plow duty. The TJ's rejuvenated the SWB fever. I know the torque peak is in the 4k range, but it's pretty (not exactly) flat from about 1800-2000 Mine truly feels ..hmmm...strained when you push it into the upper rpm range. That's not really the right term. It sure feels like the PCM puts on some virtual secondary to allow it to perform the task ..almost like an afterburner is required to get the mass at that rotational speed. It loafs along under 2500 without any objection.
 
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