oil pressure question

I own a 1997 cherokee sport 4.0

when cold, the oil pressure gauge reads about 40.
as the engine warms up after driving it drops to 20ish. while driving its a bit higher.
If i stop at a red light the gauge will sometimes read 0 and i'll get a warning light saying check gauges!

it's been doing this for sometime now. yet the engine runs nice and smooth. no ticking and lots of power.\

bad oil pressure sensor?

First step is to verify with a mechanical oil pressure gauge and go from there.

the cold and hot temps sound about right with what my gauge cluster reads out, except the drop to 0.

when you say when you stop at a red light it drops to 0. does it idle at 20 and then all of a sudden drop? or does it slowly go down? oil pressure will not make "instant" changes unless you have some sort of catastrophic failure.

My guess would be bad wiring or faulty connection. if the sensor is reading fine normally and under most conditions then it may be more a connection issue. perhaps more vibration at idle and with the motor unloaded moves a bit more and causes the connection issue.

best way to confirm is to check with another mechanical gauge if you can.

Or a good preventative fix is to check the connector, clean up the connection at the pressure sensor use dielectric grease. also check at the gauge cluster the 95 uses a connection that is known to have "issues" not sure if the 97 uses the same type or not. if you still have the problem get a gauge.

but as said, fluid pressures do not just "instantly" change unless there is some huge type of failure.

Cold oil pressure is a nearly useless measure. Typical 4.0L oil pressures when warm are 10-20 at idle, and 35-55 at 60 mph.

You must confirm oil pressure readings with a mechanical gauge, and genuine Jeep oil pressure senders are the most accurate. Lots of 4.0's have run lots of miles with low oil pressure.

the 4.0L is a monster. During cash for clunkers there were many videos showing the guys trying to seize up the motor with the blend of motor killing cocktail. the Jeeps would take the longest and require the most of the stuff to kill the motor.

Toss a sensor at it. Extremely common failure.

Thank you everyone.
I will replace the sensor with one from the dealer.
I've been running it like this for about 10,000kms now. so probably just the sensor.

you never answered do the pressure instantly drop to 0 psi and then instantly come back up?

The wiring right at the connector and the connector itself is suspect. This area is sometimes damaged by changing the oil filter from the top and the oil sender connector pins can loosen or the wiring going into the connector can be broken. When the oil pressure hits "0" again, push in on the wiring loom towards the connector and see if that gets a reading back. Replacing the connector and pigtail will fix it.

What brand filter are you running? If it's a Fram, get rid of it. I and a lot of others here use Wix.

Not to derail to much but Motorcraft FL-1 IIRC is also a replacement filter and is larger than stock. That's what I have been running for the last 4 oil changes.

the oil pressure doesn't just drop to 0. it slowly dips really low, very close to zero.
pretty sure its the sensor. will be replacing on the weekend.

My 99 XJ would slowly drop to zero at low idle when it was warmed up. I drove it like that for a number of months. I tried replacing the pressure sensor, checked all wiring etc and determined the reading to be accurate (as in, it basically had no oil pressure). It turned out my engine was just worn (crank bearings etc). I swapped out the engine (used the same oil pressure sensor) and the pressure never came close to zero under any circumstance.

northern_joe said:

the oil pressure doesn't just drop to 0. it slowly dips really low, very close to zero.
pretty sure its the sensor. will be replacing on the weekend.

Click to expand...

Do yourself a favor, and go to your local harbor freight, purchase on amazon, or rent from your local parts store, a mechanical oil pressure gauge to confirm your pressure.
Yes, more than likely your oil sender has failed. But, to know for sure is the key to keeping your heep running.