Oil pressure fluctuates at idle, concern?

[mfran12335]

I have a 2000 Cherokee sport. My oil pressure gauge drops to about 20 while at idle at a red light once warmed up and goes back up to 40 or so when driving? Do I need to be concerned?

[abebehrmann]

I remember one of the more 4.0L knowledgeable people on here once said that as long as you have 15+psi you're OK so I wouldn't worry too much about it unless it drops more.

Could just be a bad oil pressure sending unit though, mine moved all over the place when it was going bad but stopped moving so much after I replaced it.

[Mudderoy]

I have a 2000 Cherokee sport. My oil pressure gauge drops to about 20 while at idle at a red light once warmed up and goes back up to 40 or so when driving? Do I need to be concerned?

When mine was new in the South Texas summer time it would drop to 5. :( I started using straight 30 weight just because it bothered me.

[OrangeXJ]

When mine was new in the South Texas summer time it would drop to 5. :( I started using straight 30 weight just because it bothered me.

All of the 4.0's I've had (2 XJ's and the current TJ) have done the same thing once the engine gets warm. Not saying it's right but consistent. And they are all still on the road driving fine.

[nickyg]

I have a 2000 Cherokee sport. My oil pressure gauge drops to about 20 while at idle at a red light once warmed up and goes back up to 40 or so when driving? Do I need to be concerned?

That's what mine does too. I'm too concerned.

[4.3LXJ]

No, just about any engine I have had does that

[XJ Wheeler]

Sounds normal. Mine is the same way once warm. 15-20 at idle (depending on outside temp) and 40 at any rpm off idle.

Sent via messenger pigeon. I talk, he types.

[Cheromaniac]

I have a 2000 Cherokee sport. My oil pressure gauge drops to about 20 while at idle at a red light once warmed up and goes back up to 40 or so when driving? Do I need to be concerned?

You can expect the oil pressure to drop as the engine oil warms up and its viscosity is reduced. The oil pressure is also rpm dependent to a degree. The minimum should be 13psi at idle and 37psi at 2000rpm using 10W-30 grade.
If your oil pressure is a steady 20psi at hot idle and goes up to 40+psi when you increase the engine rpm, your oil pump is good and the bearing clearances are within normal tolerances.
If the oil pressure fluctuates at idle or at any steady rpm, possible causes are a bad gauge sending unit (more common) or a sticking pressure relief valve inside the oil pump.

[slvmart]

Just consider it normal, unless it drops to a lower value with the same weight oil. Most fluids will have the viscosity drop with temperature and rpm (shear). Here is a Wiki : https://en.wikipedia.org/wiki/Viscosity

[Mudderoy]

All of the 4.0's I've had (2 XJ's and the current TJ) have done the same thing once the engine gets warm. Not saying it's right but consistent. And they are all still on the road driving fine.

I was told that if the lifters are chattering the oil pressure is good. Might be time to replace the oil sensor. Mine runs around 40 psi and drops to 5 to 10 depending on the air temps at idle.