Oil Pressure Q...

88 XJ 4.0L, AW4 Auto Tranny 5k mi on reman engine. Engine running great (knock on wood, don't wanna jinx myself, lol).

I searched for Oil Pressure Questions but couldn't find any ans to my Question which is:

At idle Oil Pressure Guage is around 40psi

Driving and reving engine says 45-55psi

My Question is: What should the Pressure be when the engine is off?

When I shut off the engine it drops a little below 40 like around 30 (Ten O'Clock Position)? Should it go back to ZERO or not?

Is this NORMAL? If not do I need a new OIL PRESSURE SENDER? Please advise.

Thx.

Oil pressure with the engine stopped will be 0.Hot idle 10-15 psi,at running rpm 40+ psi is normal.
You need a new sender-
Wayne

UPDATE...UPDATE...UPDATE...

Just came in from outside while there I was more observant of the Oil Pressure Guage:

1. Engine Off says 35psi

2. Idling and warmed-up says 30psi

3. When Starting the Engine I noticed the Guage goes to ZERO and then jumps back up to 40psi until warmed-up and says 30psi.

Is this NORMAL to drop to ZERO when starting and then rise up from there? I hadn't noticed it before...strange?

Do you still think my OIL PRESSURE SENDER is bad?

Thx.

Try this, with the engine off, turn the key to the on position without starting the engine. If, the gauge reads anything other then zero, replace the sending unit.

Midnight Krawler said:

Try this, with the engine off, turn the key to the on position without starting the engine. If, the gauge reads anything other then zero, replace the sending unit.

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Hey MK,

I turnt the key to the ON Position (w/o starting the engine) and the gauge needle immediately goes down to zero and then up to almost a 1/4 position.

After starting it goes to 40psi, warmed up to 30psi

Reving and/or driving to 45-60psi.

1. Does this mean my SENDING UNIT is good or should I replace it?

2. Does anyone know what this SENDING UNIT costs and the part number (aftermarket is ok)?

Thx.

Your sending unit's behaving normally and the gauge is fine. Enjoy driving your Jeep 'cause there's nothing to worry about.

Dr. Dyno said:

Your sending unit's behaving normally and the gauge is fine. Enjoy driving your Jeep 'cause there's nothing to worry about.

Click to expand...

Exactly. Sometimes older guage clusters can behave oddly when the engine is shut off. I've seen tachometers jump to 3000 when the key is off and work fine while the engine is running, as well as other guages doing similar cocamamie stuff. Don't worry about it.

If you're paranoid, go to AutoZone and get a cheap mechanical fuel pressure guage (they cost like 10-15 bucks), then remove the pressure switch and install this guage in its place (you don't have to install the guage inside the car, just open the hood and hook it up to see what it reads). If the mechanical guage reads properly, your oil pressure is fine and just ignore the guage's wierd behavior.