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no oil pressure at idle

C

ChuckstrPT

NAXJA Member #791
Location
Birmingham, Alabama
Ok, so this is my second '01 XJ and it has developed the same problem the first had....but has progressed much quicker. When cold, reads over 30 psi at cold start..when it warms up it drops to 0 and that little "Check Gauges" light comes on. Bringing the rpm's up to near 2000 will give me 20psi. Running on the interstate, near 2500, gets me only 20 psi. As soon as the revs drop back to idle....gauge drops to ZERO. I'm not thinking this is a good thing. We did change the filter yesterday, with no change in symptoms. The oil is at the correct level.
Any input is appreciated:wave:
 
Does the oil look like a chocolate milkshake? How about the coolant, is it disappearing rather quickly with no signs of a leak?

If either of those apply, sounds like the dreaded cracked cylinder head to me. Some have said that if it cracks in the normal spot and the engine isn't too sludged up, you can take the oil cap off and shine a flash light down onto the head and see the crack.
 
UNCC_99XJ said:
Does the oil look like a chocolate milkshake? How about the coolant, is it disappearing rather quickly with no signs of a leak?

If either of those apply, sounds like the dreaded cracked cylinder head to me. Some have said that if it cracks in the normal spot and the engine isn't too sludged up, you can take the oil cap off and shine a flash light down onto the head and see the crack.
Click to expand...

Yeh, redneck was looking down there last night...didn't see any crack. Oil looks ok. Coolant looks ok too. No signs of overheating. The first '01 did have a mysterious coolant leak, and I was suspecting the cracked head, before the tree took it off my hands:doh:
 
What brand filter are you using? If it's a Fram, throw it away. If it's not a Fram, I would look at the oil pressure sending unit next.
 
UNCC_99XJ said:
What brand filter are you using? If it's a Fram, throw it away. If it's not a Fram, I would look at the oil pressure sending unit next.
Click to expand...

Yeh, we put a Mobil ! on it yesterday before the 2.5 hr drive home....and no change.....dumped a can of "restore" in it also before the drive home....no change.....hmmmm
 
sounds like a good time to get a mechanical gauge and see if the pressure is really dropping. If it is, and the oil isn't diluted with coolant, you'll probably be changing main and rod bearings after a two hour trip with low pressure.

If the engine isn't making odd noises or running hot, I'd say you've still got some pressure though.
 
Shorty said:
sounds like a good time to get a mechanical gauge and see if the pressure is really dropping. If it is, and the oil isn't diluted with coolant, you'll probably be changing main and rod bearings after a two hour trip with low pressure.

If the engine isn't making odd noises or running hot, I'd say you've still got some pressure though.
Click to expand...

Yeh, temp was good the whole trip. I'm under the impression that 20 psi is not nearly what it should be at 2500-2800rpm...so there was some, but not good pressure on the highway. I'll go listen to it again....
Thanks:wave:
 
my 2000 xj idles at about 20psi and 1200- highway speeds it sits at about 50 psi, but i run royal purple oil 10w40 and royal purple filter.

what viscosity of oil are you running? a thicker oil will boost oil pressure... but im thinking your problem lies in the oil pump itself
 
Ok, well that rules out the filter. As mentioned, put a mechanical gauge on it to verify what the pressure really is. This will determine if the sender unit is faulty or not.

Cold idle pressure should be around 45psi
Hot idle pressure (after driving around a while) should be around 20psi (w/ 13psi minimum according to the FSM)
Cruising psi should be in the 40-45psi range depending on RPM's.
 
Well....no strange noises with it running...still not getting much pressure even at cold....that ISQ. So I guess I need to go borrow a pressure gauge from Autozone....hmmm
and as for oil.....dunno....I got it at 140k, and I've only but 1700 on it since May...the PO changed the oil right before purchase. hmmm:scared:
 
You are on the right path--put a mechanical gauge on it to see if there IS a problem.

If the mechanical gauge readings are essentially the same, then you have problem(s) other than a bad sender.

Smell the oil--is it fuel contaminated?
 
so, Autozone doesn't HAVE a mechanical gauge...for loan of sale....and neither does Sears. Any suggestions on where to get one??
Thanks.
 
ChuckstrPT said:
so, Autozone doesn't HAVE a mechanical gauge...for loan of sale....and neither does Sears. Any suggestions on where to get one??
Thanks.
Click to expand...

Harbor Freight is your friend :)

A handy tool that is worth investing in keeping, in my opinion.
 
ChuckstrPT said:
so, Autozone doesn't HAVE a mechanical gauge...for loan of sale....and neither does Sears. Any suggestions on where to get one??
Thanks.
Click to expand...

Of course it has to be a Sunday.

There has to be other parts stores in Birmingham--got Schucks/O'reilly/Kragen?
 
Solution....put on a mechanical oil pressure gauge....50+ pounds cold....stabilized near 30 lbs at idle.....replaced the sending unit. Done.
Thanks Vortec!
 
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