Oil pressure sending unit question

Coldstrat

Coldstrat

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Joined
May 13, 2021
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11
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Colorado
Need help understanding oil pressure sensor.

When I cold start my TJ (99 4.0l), the oil pressure reads 40. Once warm, the pressure drops down and is based on RPM... 2k RPM = 20. My worry is that at idle, the pressure Guage will, occasionally, drop so low that the check engine light will illuminate. Increase RPM and needle rises accordingly. Oil is at correct level (5w-30.. cold here).

Do I replace the sensor? Something odd going on.

Thanks
 
Best bet is to confirm pressure with a gauge on the oil rifle. If that’s not possible for you it wouldn’t hurt to change the sensor with a quality replacement.

You can check and see if the electrical connector has oil in it.
 
My thoughts are that you might actually have an oil pressure problem. When was the last time you changed the filter, oil, etc?

The reason that makes me lean towards the oil pressure problem is that you didn't mention the gauge being erratic, and it seems to give you consistent results.

It can be something as simple as a clogged oil filter or as bad as you can imagine, or the sensor, but I don't have enough experience with the TJ oil pressure units to be able to comment on what a common failure mode for a TJ sending unit is, I am sure others can comment.

One thing I know for sure, don't ignore it.
 
Coldstrat said:
Need help understanding oil pressure sensor.

When I cold start my TJ (99 4.0l), the oil pressure reads 40. Once warm, the pressure drops down and is based on RPM... 2k RPM = 20. My worry is that at idle, the pressure Guage will, occasionally, drop so low that the check engine light will illuminate. Increase RPM and needle rises accordingly. Oil is at correct level (5w-30.. cold here).

Do I replace the sensor? Something odd going on.

Thanks
Click to expand...
Your pressure going up and down in direct step with the engine rpms is 100% normal since the oil pump is engine driven. 10 psi per thousand engine rpms is the time-honored rule of thumb for acceptable oil pressure.

Dropping low enough to light the Check Gauges light is not normal however, I'd guess nothing worse than a bad oil pressure sender which is easily replaced. I'd try to find a Mopar replacement, or at least avoid all store brands like Duralast from Autozone which are junk. Check them out at Rockauto.com, avoid their economy senders, go with their daily driver versions.
 
Thanks for feedback. Guage behavior has been consistent (odd) across a couple of oil/filter changes.

Jeep is due for another change (perform every 5k miles) soon, will go ahead and swap out sensor while I'm there.
 
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Reactions: Jerry Bransford
Doesn't strike me as a sender issue, but perhaps you'll get lucky.

How many miles?
How long have you owned the jeep?
How long has this been occurring?
 
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