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low oil pressure at idle when warm

B

bwickett

NAXJA Forum User
Location
SoCal
Hey, I've searched for everything I could and have had to resort to posting this. I have a 2000 4.0 with 58,000 miles on it. The oil pressure is fine when it is cold and when I am driving, but once it gets hot and starts to idle the pressure immediately goes to zero. I changed the sending unit, I have no leaks, and this all started happening after I overheated my engine about two weeks ago. The first thing I did was to have the oil changed on my lunch break, they put in 5w30 and didn't help. Sending unit didn't help. I don't seem to be mysteriously losing coolant either. Then a few days ago I started to get a "fluttering" sound in my engine. Sounds like an exhaust leak but it seems too coincidental to not possibly be something related. I am worried that I going to kill my engine if I continue driving (and I'm sick of revving my engine at stop lights) Any ideas?
 
My guage does wiref things too. Like when I start it it will stick at zero for a few seconds then jump up. But mines a 89, quite a bit older. Have you checked the actual oil level, just to be sure it's full? I think the oil pump is gear driven so if your engine running fine, it should be pressurizing.

For the coolant check under the engine to see if you can find any antifreeze drips. When water pumps go they will leak a little bit out of the weap hole untill the quit.

A exhuast leak wouldn't be uncommon as alot of XJ have them but I wouldn't think you would yet as your still low in miles.
 
If you overheated the engine, it's possible that you scored one or more of the bearings. 5w30 is not a very heavyweight oil to try if you're having pressure problems. I'd suggest doing another oil and filter change. Try Castrol 5w50 or Mobil-1 15W50 synthetic with a good brand filter like a Purolator and see if that makes a difference. If not, drop the oil pan and replace the main and rod bearings.
 
Is there a reason to rule out the oil pump? Just wondering. What about the fluttering?
 
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i'd prob do an oil change like Eagle said but after that try to find a mechanical guage to read oil pressure. i know on my boat there is just a guage with a hose going to the block in a pressureized area of the oil. and it reads the pressure. bet you could find a friendly shop or person to lend u a mec gauge.
 
No reason to rule out the oil pump, but I didn't see anything suggesting that anyone had ruled it out. But the internals of the oil pump are less likely to be affected by the extreme viscosity reduction you'd get if the engine overheated badly, which is why I think the next step if heavier oil doesn't work should be to replace the bearings. Yes, you can just "inspect" them -- but bearings are cheap and labor isn't. The added cost for new bearings once you have the pan off isn't much, and it eliminates any uncertainty.

I don't know what a flutter sounds like. To me, a flutter is something I feel when driving, an irregularity in the power curve, not a sound. Can't help you there.
 
When that happened to me (on a road trip to the Badlands no less), I dumped in heavier oil and it helped out a bit. Kept it from dropping all the way to zero at least. When I got home I relayed the "adventure" and a fellow Jeeper told me about problems that Fram was having with collapsed filters or something like that. Sure enough, I popped the hood and there was a Fram. I swapped out the filter (which I hadn't done when I changed the oil 'cause I assumed it was an internal problem with the engine) and the problems went away. :D
Oh, and a few years ago the same sort of deal happened, but that time it was due to my rear main seal getting waaaay worse all of a sudden and the engine was down to under 2 quarts. :laugh3: D'oh!
Not sure if any of this will help you out any, but maybe someone else reading this can benefit.
Jeep on!
--Pete
 
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Eagle... the "fluttering" sounds like a puff of air or a tick sound that changes speed is relation to the rpm. On my 86 xj it was the exhaust manifold but I haven't had any free daylight hours to investigate on the 2000. I've read about "lifter knock" what does that sound like? Thanks
 
bwickett said:
Hey, I've searched for everything I could and have had to resort to posting this. I have a 2000 4.0 with 58,000 miles on it. The oil pressure is fine when it is cold and when I am driving, but once it gets hot and starts to idle the pressure immediately goes to zero. I changed the sending unit, I have no leaks, and this all started happening after I overheated my engine about two weeks ago. The first thing I did was to have the oil changed on my lunch break, they put in 5w30 and didn't help. Sending unit didn't help. I don't seem to be mysteriously losing coolant either. Then a few days ago I started to get a "fluttering" sound in my engine. Sounds like an exhaust leak but it seems too coincidental to not possibly be something related. I am worried that I going to kill my engine if I continue driving (and I'm sick of revving my engine at stop lights) Any ideas?
Click to expand...

An oil pressure that drops to zero at idle when the engine's hot but is OK when the engine's cold is almost certainly due to worn main/rod bearings. Since the problem was preceded by the engine overheating, the oil probably became too thin to protect the bearings and you've toasted them.
You could try a heavier grade of oil, say 20W-50, and see if things improve. The thicker oil will partially compensate for the increased bearing clearance so your oil pressure might not drop right down to zero but to 5-10psi instead. It's only a temporary bandaid though and you'll still need to replace the bearings.
Why did your engine overheat in the first place? Coolant leak? Stuck closed t'stat? Since you overheated the engine enough to toast the bearings, you may well have blown the head gasket or cracked the head as well.
 
Before chasing a problem that may or may not be there, hook up a mechanical gauge and check the pressure. Factory specs say a minimum for around 12psi at a hot idle.
 
My wife has been driving my 2000 after parking her 95. The 2000 has 150k on it and started doing this same thing yesterday morning. Good pressure till it gets good and warm. I noticed that the sesor had oil in the electrical plug and was also leaking where the plastic and metal halves are crimped together. I hope that takes care of it. I know when the sensor went out on the 95 that the oil pressure gauge was all over the place it did not just drop when warm like this one. On the 2000 it acts just like it it should and then it is like it reaches some temp where it just starts dropping off. Unlike yours my jeep has never been overheated.
 
Jay3XJ+ said:
My wife has been driving my 2000 after parking her 95. The 2000 has 150k on it and started doing this same thing yesterday morning. Good pressure till it gets good and warm. I noticed that the sensor had oil in the electrical plug and was also leaking where the plastic and metal halves are crimped together. I hope that takes care of it. I know when the sensor went out on the 95 that the oil pressure gauge was all over the place it did not just drop when warm like this one. On the 2000 it acts just like it it should and then it is like it reaches some temp where it just starts dropping off. Unlike yours my jeep has never been overheated.
Click to expand...

Have you changed the filter since this started happening?
Jeep on!
--Pete
 
Pete M said:
Have you changed the filter since this started happening?
Jeep on!
--Pete
Click to expand...


No not yet, I plan to do that as well...She just parked it I only looked long enough to see it was leaking around the sensor...
 
Replacing the sending unit seemed to not help. Had a reputable mechanic change the oil using 10w30 and check the oil pressure using a mechanical gauge. The gauges were reading significatly higher than the in dash unit.
The in dash shows around 12 to 13 psi at idle and the mech. gauge showed 20-30. At high RPM the in dash = a tad over 40 and the mech. gauge showed 50-60. The in dash used to show exactly what the mech is showing now. Perhaps the problem is on the gauge end and not the sending unit....


SO....
I guess now I need a good mech gauge to mount in the jeep because I am becoming parannoid because of the 150K miles. I need it to last another 50-60k Any sugestions on a good gauge so I can keep my eye on things.



 
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