low oil pressure at operating temp

[bosco01xj]

I'm curious why my oil pressure has been a little low lately. When I start my jeep I'm at over 45 psi. After I drive around a bit, especially on the interstate, the oil pressure reads a steady 40 but when slowing down to city speeds the pressure drops to 20-25 psi. When I actually stop at a light or stopsign, the oil pressure reads 10 sometimes 15.

I'm using rotella t 15w 30 with a wix filter. 4.0 liter inline 6 123,000 miles.

 

[UNCC_99XJ]

Assuming you have a 2001...

First, verify that the gauge is showing accurate. Grab a mechanical gauge and put it in place of the sending unit. Have a friend start the Jeep cold and watch to see what you get on the mechanical gauge. Keep it running until it gets nice and warm and see how low it drops down.

If the mechanical gauge confirms what you're seeing on the dash, open the oil cap, shine a flashlight down and see if you see a crack in the head. On the 0331, they usually crack where you can see it by looking down the oil cap. If the mechanical gauge shows consistent higher readings, replace the sending unit.

Noticing any coolant disappearing? Does the oil look like a chocolate milkshake?

 

[bosco01xj]

It is a 2001. I actually have noticed recently that my coolant does dissappear. The oil does not look like a chocolate shake though.

 

[Cottontail]

Go to an auto store and get some UV liquid to pour into your radiator. Get the UV glasses and flashlight. Then drive the Jeep for awhile and circulate that coolant/liquid mix through the ENTIRE system. Then put on the glasses and turn on the flashlight and look for the glow.

That liquid will glow like it was under a blacklight. Pop open the oil filler cap and see if you see the glow on your head. If not, no crack. THen look all over the engine compartment to see if there is any coolany leaks anywhere.

I suspected a cracked head in my '01 and didn't end up seeing anything under the valve cover, but found other leaks.

 

[Rmart30]

It is a 2001. I actually have noticed recently that my coolant does dissappear. The oil does not look like a chocolate shake though.

On the 2 I had with 0331 heads that were cracked neither made the oil milky. If I took a CLEAN yellow plastic drain pan and changed my oil I could let it sit a hour or so then go and slowly pour out most of the oil and the green coolant droplets in the bottom of the pan almost glowed.
The yellow pan lets light show up thru it where a black one doesnt.

 

[MELKORsXJ]

Those are about the same psi readings I get from my guage cluster... I have a 2000, with an 0331 head. It has cracked on me once, when I first got the jeep in 07. I've had no other problems, and that is the factory spec for the oil pressure. 10-11 psi at idle, 25psi @ 2500rpm, 35psi @ 3500rpm... basically just take the first two numbers, and your oil pressure should be about there...
Not sure if this helps, but thought id share I have had the same readings for a few years now, with no problems... and I haven't noticed coolant missing either.

 

[mshanejolly]

2000 XJ, 4.0L, All Stock, 159,000miles

I have a similar but different oil pressure problem. I have around 35-40psi while running at highway speeds at temperature. Usually 40+ at cold start-up. When hot at idle, the oil pressure will drop to NOTHING and I get the "Check Gauges" dummy light. Put it in Neutral and rev the engine a little and oil pressure comes back up. I'm scared, really scared that this is the oil pump. Any thoughts?

 

[UNCC_99XJ]

2000 XJ, 4.0L, All Stock, 159,000miles

I have a similar but different oil pressure problem. I have around 35-40psi while running at highway speeds at temperature. Usually 40+ at cold start-up. When hot at idle, the oil pressure will drop to NOTHING and I get the "Check Gauges" dummy light. Put it in Neutral and rev the engine a little and oil pressure comes back up. I'm scared, really scared that this is the oil pump. Any thoughts?

Same thing as I told the OP. Verify what your oil pressure actually is by use of a mechanical oil pressure gauge. If your pressure, particularly at idle, is higher than what your dash gauge is telling you, replace the sender unit. If the mechanical gauge shows what the dash gauge is showing, start looking for a cracked head.

 

[ChuckstrPT]

2000 XJ, 4.0L, All Stock, 159,000miles

I have a similar but different oil pressure problem. I have around 35-40psi while running at highway speeds at temperature. Usually 40+ at cold start-up. When hot at idle, the oil pressure will drop to NOTHING and I get the "Check Gauges" dummy light. Put it in Neutral and rev the engine a little and oil pressure comes back up. I'm scared, really scared that this is the oil pump. Any thoughts?

I had the same exact problem w/my '01...if you can't find a mechanical gauge, just go get a new sending unit and change it. I can't remember how much it was, $14?? Problem solved. It was very disconserting...but never "sounded" bad, or behaved badly...just PSI dropping....:wave:

 

[mshanejolly]

New sending unit didn't fix the problem. I still need to put the mechanical gauge on, but indications are that it has oil pressure. Otherwise, I would expect the engine would make a lot of noise when the pressure drops off. Any other ideas?

2000 XJ, 4.0L, All Stock, 159,000miles

 

[Team Willys]

My 2 cents worth...

You would have to run an engine for at least 10 mins with 0 oil pressure for any damage to occur. There is no load at idle, so not really any heat buildup, and the oil film on the bearings is enough for a bit. The lifters will collapse before a bearing gets damaged. Do the rocker arms start clicking after idling for a few minutes? Also, pull the oil cap off and look at the top of the rocker arms while its idling and see if there is plenty of oil flow going across them. If there is, it could possibly be a partially blocked oil passage in the block.

 

[j_epcherokee]

I had a similar situation with the 2000 I just picked up. Good (40psi) oil pressure on startup, and dropped as it warmed up. Talked to a Chrysler tech at work, and looked up some info.

The oil pressure switches in these get real sensitive to temperature over time.

If you have access to scan data, the voltage reading should be 5V unplugged, and check the ground path for resistance. If both of those are good, your wiring isnt to blame.

Next, check the pressure with a mechanical gauge, if the pressure is good, your sending unit is junk.

I priced a few sending units, and got one at cost through work for $40. AutoZone sells them for around $50, but expect to have difficulty with them either out of box or in the future. A quick search on IdentiFix showed me many shops had problems with aftermarket units, so I went ahead and installed a new OE unit. Works perfectly. Aproximately 45psi at cold start and now just under 20 at warm idle.

 

[Talyn]

You would have to run an engine for at least 10 mins with 0 oil pressure for any damage to occur. There is no load at idle, so not really any heat buildup, and the oil film on the bearings is enough for a bit.

The main culprit in bearing damage isn't the low oil pressure at idle. Its the fact that coolant + oil make an acid that eats the bearings.

 

[bosco01xj]

This is thread was brought back from the dead. Lol.

 

[j_epcherokee]

Re: Re: low oil pressure at operating temp

This is thread was brought back from the dead. Lol.

Yeah, I'm sorry. My fault, but I blame Google....

 

[shelbyluvv]

Never hurts to add new info.

I wish my Jeep had those oil pressure readings. I have 20# cold and 0-1# hot. It sounds like hell but somehow has stayed together for a couple months!