Originally Posted By: Zaedock
Originally Posted By: dlundblad
Originally Posted By: Zaedock
Your 4.0L does not require a daily dose of ZDDP. SM/SN rated oil has plenty for the factory low tension valve springs. I like the 5W30 SOPUS GrpIII synthetics, but if the TDT has been working well for 50K, why change?
I have always felt that 2.5/4.0/258 engines have only adequate valve train oiling and have repaired about a half dozen noisy lifter Jeeps with a HV Melling oil pump. In my experience, the factory oil pump life expectancy is about your mileage anyway, so you may want to look into it.
With your experience? That's a new one on me. Even after a quick google search a failing oil pump isn't that common. I even gave it the benefit of the doubt by rewording my search.. still nothing much. Not saying they never fail, but they normally last the life of the engine.
I have quite a bit of experience rebuilding Jeep 2.5/4.0/258 engines. I think I may have a 199 or 232 under my belt too. I also have a lot of experience driving these engines in very precarious off road situations. By life expectancy, I don't mean absolute failure. The oil pump can "last" for 300K miles, but it loses efficiency. Google Jeep tick and you'll find countless threads on the dreaded issue. I have repaired several of the tick issues during rear main replacement by installing a Melling HV pump at the same time. In one severe case (I mean it was a LOUD lifter tick!) it was night and day. My friend thought I swapped engines!
Google 4.0L and allpar for more info on the 4.0L.
Originally Posted By: Miller88
I'm a light oil person where it's warranted, however, in the case of the AMC 4.0 - the UOAs show that they wear less on a 40 grade oil.
Will it make any difference in the life? Probably not.
The best 4.0L UOA I've seen on here was on Havoline 10W30. The Fe numbers were insanely low. I also achieved single digit numbers during a wheeling season on the $.99/gal Delo SAE30 I scored years ago. So far, The 2.5L in my trail rig likes the QS UD 5W30. The Fe numbers were very low and the drivability is so much better with the lower viscosity compared to the SAE30 or a XW40, especially with the start/stopping on the tougher trails.
I have also been around 4.0's my whole life and have never had or heard of an oil pump failure......
BUT it would make sense and could cause lifter tick with lost pressure, at the same time I would think your oil PSI gauge would display a change in pressure that would effect lubricating your lifters. I also understand mechanical parts loosing efficiency with wear (it is a gear typr pump) and using a heavier oil would probably increase oil pressure and quiet a tick caused by less oil pressure.....
I was always under the impression that the tick was related to the surface mating between cam and lifters (flat tappets)