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I have a 1997 Jeep TJ Wrangler 4.0 with 171K miles on the clock. This mechanic at work is making me very nervous telling me that the oil pump on the 4.0L takes a dump between 150 and 200 thou miles and I should be aware of this..Im a worrier and he's got me going now. Anybody have any input on this and what I should do? the engine runs great. When I start it cold it has 50 lbs oil pressure. when its warmed up its 40 while driving and 20 sitting at a light. Sounds normal to me but have any of you had issues with the oil pump? He says when it goes its too late..New motor time..

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Superwinch...I don't have a crystal ball but can share that the Jeep 4.0L oil pump is as reliable as any other engine's pump.  I use Melling high-volume replacement pumps at rebuild time, but I've never had a Jeep inline six-cylinder oil pump "fail" between normal engine overhaul points.  Your oil pressure sounds reasonable and consistent with most other 4.0L engines at this mileage, and there's a good likelihood that the oil sender has some restriction, making the gauge read low.  A pressure test with a mechanical oil pressure gauge could eliminate any guesswork here.  As a point of interest, the CJ and early YJ 4.2L senders were notorious for clogging and making the gauge read low.

50-plus PSI would be better above 1600 rpm, but normal 4.0L pressure according to Jeep is 37-75 PSI at these speeds.  Your engine reads lower on the oil pressure range, but this does not indicate a pending oil pump failure.  My guess is that the 40 PSI reflects normal wear in the engine, in particular crankshaft and camshaft bearing clearances and, to a lesser extent, the oil pump gear clearances.  The pressure relief valve on your stock 4.0L oil pump is set for 75 PSI, and this produces enough pressure and flow volume to maintain the necessary lubrication throughout the engine.  If the engine has the same oil pressure as it did tens of thousands of miles ago, I'd call it good.  Is that the case? 

Note: My '99 XJ's 4.0L OEM pump has nearly as many miles on it as yours, which does not concern me. If I were doing a somewhat common rear main seal replacement with the oil pan down at this mileage, I might install a new Melling high-volume oil pump and new oil pump pickup screen as a practical consideration.  But I cannot see dropping the oil pan just to change the oil pump.  That can wait until the inevitable need to completely rebuild your engine, which I would project as 200K to maybe 225K miles.  Had my engine run synthetic oil since day one (we bought the vehicle at 94K miles), I would expect 250K-300K miles from the factory build.

Now, if you want to worry about something that might wear out before the entire engine needs rebuilding, consider the valve timing chain and gears.  These do last to 150K-200K miles, and if the chain does begin to "go", you'll have advance warning in the way of chain noise or a camshaft position sensor MIL Check Engine code.  The chain seldom breaks, they generally loosen, even rattle, and retard the valve timing.  This retards the ignition timing as well, and there's a general loss of performance at lower engine speeds.  On your 4.0L engine, a trouble code for the camshaft position will indicate that the camshaft position is lagging behind the crankshaft position.

As for engines and wear, your friendly mechanic at work likely has experience to back up his comments.  I have seen rare cases where the oil pump/distributor drive gear pin shears or the gear teeth strip, and this causes the distributor's driveshaft and oil pump to stop rotating.  With your engine design, the distributor rotor would also stop turning, and that means the engine has stopped running.  There's little "surprise" element here.

How long have you owned this Jeep, and are you aware of the engine having major work at any time?  What kind of oil and filters do you use, and how often have you changed oil?  This has a large impact on how long you can expect the engine to run without major work.  My view is that a running engine is money in your pocket.  You will inevitably need to rebuild your 4.0L engine if you keep the TJ.  However, each day that you get reliable service from the current build is added value.  You'll have ample forewarning and time to plan your 4.0L inline six rebuild.  These Jeep sixes are among the most reliable and fundamentally forgiving gasoline engines ever built.

Moses

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Thanks so much for your input. I have only owned the Jeep since December. I hit a deer with my  caravan and got totaled. I had that since new and had 254 thou on it. As far as the Jeep,it had 168 when I bought it. Got it home and changed the oil. I like Pensoil syn 10/40 with a fram filter. I changed the plugs,wires,cap  and rotor. Flushed the cooling system. Did a tranny service changing the oil and filter and I put a new pan on it that holds 2 more qts and it has a drain plug. 2 wks later I drained it again and put fresh oil and 2 wks after that drained it again and put the required oil in. Darn expensive 8 bucks a qt. I also adjusted the bands. shifts a lot better and It might last a while if I don't beat on it. Im 67 yrs old so those days are long gone. I only put 22mi a day on it back and forth to work. Had to put a new feul pump in and now it starts first time every time,I love it. Oh and by the way im a big fan of Motorcoat so that's a plus in motor and trans. Ran some Seafoam in the tank. If anything happens to the trans or motor its worth it to me to replace it. The Jeep was garage kept and the frame and body has no rust at all..You have a great site and I really appreciate your input..Thanks Moses..Pete 

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Pete...We have a lot in common with both our Jeep vehicles and our matching ages!  Sounds like you found an exceptional Wrangler with just higher miles on it.

The 32RH transmission likely did need attention on your Jeep, this was the "weak link" for these early TJs, though it was not a transmission weakness.  The unit is the classic 904/999 with electronic controls and a lockup converter.  Its issue off-pavement was dry sumping when the vehicle was on a steep angle.  The loss of fluid at the filter would cause the transmission to run intermittently without fluid under these conditions and cook the bands and clutches.  Your Jeep apparently escaped this fate, what you have encountered suggests that the vehicle was not "hardcore" four-wheeled.  

Did your dropped pan include a spacer for the filter?  If so, the filter rides deeper in the pan, which reduces the risk of dry sumping, the most significant advantage with some deep pan kits.  Then there are the inherent design concerns, and you will want to at least review my article on the Ram and Jeep RH/RE needs:  http://www.4wdmechanix.com/Survival-Upgrades-for-Jeep-and-Dodge-Ram-Automatic-Transmissions?r=1.  Watch for symptoms I describe in the article or apply the preventive measures if practical.

From what you have encountered, this Jeep was very well maintained.  Did you get service and repair records to know what work has already been done?

Moses

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