New to the 4.0L jeep and wondering what avg. oil pressure runs (idle/~2500RPM) for the 4.0L? When I start my Jeep cold, it sits around 80 and when its hot at idle is sits around 40. That seems pretty high to me especially for 134K miles. I did some searching and everything I find is people having defective sending units, but they say they are always pegged at 80 and don't move. Mine seems to work the way I would expect (reads higher when cold, a bit lower when warm and varies with RPM accordingly), but the values seem a bit high. Is this normal for this engine or is something else going on here?

 

sounds good to me......i see 65ish when cold and 40-45 when at cruise...1,800+

 

what weight oil you got in it?

 

mine 2001 jeep Cherokee Sport oil pressure runs 50 psi 2200 rpm and idle is 20 sounds like yours is running a little high side - could be sending unit going bad.

 

when warm you should have around 20-25psi at idle, and 40ish at over 2000rpm according to haynes and chiltons, you probably have the wrong grade of oil get a thinner viscosity oil, or the oil filter is clogged, which changing it would fix it, i would check those first

 

Jeep oil senders are not known for their precision. If you really want to know what you are dealing with, get a mechanical guage and hook it up temporarily and compare. FSM oil pressure specs on the 4.0 are 13 psi @ 600RPM and 37-75 psi @ 1600 RPM and higher.

 

what grade oil are you running

 

regular Castrol 10w-30. Didn't figure I would need anything thinner in an engine with over 100K on it.

 

Yes, if you're running 10w-30 then those numbers do sound a bit on the high side. You're not running any kind of an oil additive are you? Perhaps trying changing your filter and using a different brand? Was the engine neglected, do you suspect there's build-up inside the engine?

 

my vote goes for the sending unit. When they go bad they won't always be pegged or not move, its common for them to read higher than normal pressure or lower than normal pressure. They aren't hard to replace so I would start with that. Most are broken when they get banged into while changing the oil filter. Start with the simple stuff first

 

Rule of thumb, 10psi for every 1000 rpms.

 

your beating a dead horse using the stock guage for a 100% reference.....PERIOD. hook up a mechanical guage stop guessing.

 

I just replaced mine this week. It was reading 50 at start and then would go to 80 and stay there. After replacing the sender and checking it with a mechanical to verify it now reads 50-60 at start cold and after hot at idle reads 20-25.

 

I'm just a bit unclear about the switch versus the sender.

Is this what the sending unit looks like for the oil pressure gauge?

 

^^^^^yes...oil pressure sender