jeep oil pressure problems

[hansj3]

My 97 Jeep Wrangler, with the 2.5l out of a 87 wrangler, that I brought back from the dead Is having a weird issue. When its hot it runs 45 psi But when its cold the gauge slowly works its way down and then tanks to 0.
I have a mechanical gauge I'll be at a cheap one and when I hook it up after i get zero on the dash I still have 20 pounds pressure
Would the oil cool off that fast as to thicken up in that time?
I'm running 15w40 delo but I'd like to thin that out for winter.
I'm not worried about pressure, I've read the pressure hot, and its 3 times minimum hot spec, and theres no telltale signs, eg. Lifters.
I have replaced rod bearings and rebuilt my oil pump, but i cant tell if the housing was good.
I think im just going to go get a melling hv pump

 

[Brybo86]

Any way to put an electrical testing gauge on the oil pressure gauge wires?

 

[Johnny2Bad]

First thing is to check with a known good gauge; gauge failure is reasonably common with Oil Pressure gauges. You don't have to be driving, can be done from under the hood.

Just get a reading on your old gauge, substitute the new gauge and see how it matches up. Chances are there will be a big discrepancy if the gauge is the issue, especially at one or the other of the scale (eg at 0 psi or 60 psi).

" ... I have a mechanical gauge I'll be at a cheap one and when I hook it up after i get zero on the dash I still have 20 pounds pressure ..."

I'd say "bingo" on a bad gauge.

[took me a moment to figure out "... I'll be at ..." which is why I didn't nail it right away. You mean "albeit". Not language police, just a laugh cuz it went past me at first].

https://www.google.ca/#q=albeit

 

[hansj3]

[censored] autocorrect

 

[SwampSurvivor]

20 hot PSI is within spec for the AMC150 engine.

The Jeeps of that era have the pressure sensor mounted on the filter housing. They get flaky after 20 years of oil changes.

 

[Chris142]

Sensor or gauge problem

 

[Kuato]

Faulty gauge sounds right to ke too. Thinner for winter? Engine specified for 5- and 10w30 right? At least my '97 2.5 was.

 

[salv]

bad oil pressure sensor or gauge. common jeep issue.

 

[440Magnum]

Sounds like a faulty electrical gauge sending unit to me, although they usually poop out when they're hot worse than when cold. But they fail often, and they're pretty cheap, replace it and I'll bet the problem goes away.

 

[hansj3]

After months of thinking about this, I decided to look up how a oil sender works. They are pressure variable resistors. on the ground side of the circuit... and the gauge has read low...

Maybe I should go ohm out the ground side of the harness...

 

[PierreR]

Replace the oilpressure sensor.
They are the very fisrt thing that fails on jeep engines.

They are also known for being more of an fancy "idiot light"
IE dont trust them so much, if your mechanical testguage shows pressure there is.

Oilpressure at idle should be at around 25-35psi
At 1600+ rpm around 37-75 psi