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Something is different, don't know what?

Demonoid369

NAXJA Forum User
NAXJA Member
Location
Salem, OR
So I've had my 97' 4.0L jeep for almost a year and after a few months I got lucky and found a full gauge cluster to swap out my dummy light ones. Afterwards I kept a good eye on the oil pressure and up until now its been pretty much 100% consistent with being a hair under 40 at hot cruise and 20 at hot idle. But lately I've noticed the oil pressure at 35 ish at cruise and 10-15 at idle? Nothing has change with the oil and filter(Dino oil/napa gold filter) so I'm kinda stumped as to maybe the oil sender is fritzing? It's got 200k miles on it. Haven't done a mechanical gauge yet but was hoping to get some ideas as to why the pressure seems to have gone down. Any ideas?
 
My bet is wear and oil breakdown when warm.
35 psi on a 200k engine is decent.

You already run a decent filter. I run 10w30 and change it every 3k, or once a year, whichever comes 1st. Synthetic is more stable when warm, but is more $.
 
My bet is wear and oil breakdown when warm.
35 psi on a 200k engine is decent.

You already run a decent filter. I run 10w30 and change it every 3k, or once a year, whichever comes 1st. Synthetic is more stable when warm, but is more $.

Ya I know 35 and 10-15 isn't bad, it just has me curious as to why the change since its been so consistent for the last 8 months. Figured if I could get ideas maybe I can figure it out before it could/possibly turn bad. Not worried at the moment, just curious lol. Last oil change was 1k ago, and I change it every 3-4 thousand miles.
 
Could it be that Summer is upon us? For the last 8 months (here anyway) it's been under 100 degrees outside regularly. In the recent weeks, temperatures are climbing, and as such I have seen slightly higher temps on the gauge. While my coolant is only getting slightly warmer I imagine that on these 100 degree days the oil gets a good amount hotter, thus causing a little lower pressure. I also tend to run in the same ranges as you, and have recently seen this behavior from my Jeep.
 
First rule of XJ Club when it comes to oil pressure:

Put a mechanical gauge on it.

Peace of mind; priceless.
 
First rule of XJ Club when it comes to oil pressure:

Put a mechanical gauge on it.

Peace of mind; priceless.

That's what I'm gonna do as stated in first post. Just figured I'd get some other opinions as to what else lol would warmer day in a way cause the pressure to be a little less? Makes sense in a way.
 
That's what I'm gonna do as stated in first post. Just figured I'd get some other opinions as to what else lol would warmer day in a way cause the pressure to be a little less? Makes sense in a way.

With Dino oil, yes.

Synthetic blend or full synthetic will hold up to higher heat better than Dino.
 
Toss some synthetic 5w40 and and call it done. Doesn't drop off as much when warm and quiets the lifter chatter. Best choice I made so far.

My 4.0 was the same when on the highway, don't get thev heat as much up here. On 500km runs to work I'd see a drop after an hour of driving. Usually about oil change time in winter and always during summer.
With the 5w40 syn ... No longer happens.
 
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