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Low oil pressure

M

Mbjeep91

NAXJA Forum User
Location
Arlington Ohio
2000 XJ Classic, 4.0L, A/T, 163K, The jeep had a cracked head when I bought it, I replaced the head and am now running 10w40 with a napa filter, When the jeep reaches operating temp. the oil pressure falls to about 12 psi, when driving down the road it is around 40 psi, my guess is that the main and rod bearings are shot as result of coolant in the oil, my question is can i replace the bearings with the engine still in the jeep and do i replace the oil pump as well? any input would be greatly appreciated.
TIA
 
First thing I would do before you jump to that conclusion is verify with a mechanical oil pressure gauge that the pressure really is doing that at hot idle. The oil pressure sender unit's do like to go out.

If everything checks out, then I would look at opening the motor up.
 
X2 on the sending unit. A 3 minute replacement job too.
Yes you can do the bearings from under the jeep. I hear it's a bit tricky to get the pan off with the front axle in the way. But yes it can be done. Is it knocking??
 
Once you've checked the sender, consider the fact that replacing the bearings will probably bring up the pressure for a steep price in labor.

The low buck method is to pour in a can of Slick 50 and watch the pressure jump 15-20 pounds across the gauge, then run 15-40 to keep it up. With a nine year old vehicle, there are worse things that could happen.

I've got 195k on my '90 and it's still strong, having had 15 pound pressure at hot idle for years.
 
has he not got good pressure? Ten psi per thousand revs as the golden rule of thumb for ANY engine hes well within. Hes not using thick oil specially with the age and mileage. Hes got great flow. I know the manual for jeeps says a low point of 13? But if no other issues and verified psi, whats the problem, i dont get it? I get 40 on start up and running and would like it lower. But my low point is 9psi at hot idle which is as low as i would dare go so im stuck with 40 on start up?
 
My 98 shows a low oil pressure at a hot idle. I have yet to have any problems at all, and was told 1 psi per 100rpm is acceptable. I wouldn't worry about it too much, if you really did have a VERY low pressure you would know by the sounds the engine made.
 
So where is the problem?

Verify your oil pressure with a mechanical gauge. If your numbers are correct, there is nothing wrong.
 
Thanks for the input, really the engine has no abnormal sounds, at least not any my other to xj's don't have... I was just worried because of the coolant being in the oil and the fact that I read on Mitchel On Demand that the idle oil pressure should be around 20 psi.

I will verify with a mechanical gauge and if different change the sender. Other than that I guess i'll let it go till it starts makin funny noises.

Thanks again!!
 
I have a question about replacing the sender. Is there a different sender for 4.0's with the gauge versus the idiot light?

My XJ came with the idiot light cluster, and I swapped for a gauge cluster. When I started it, the starting pressure showed at 40 to 45 PSI on start up/short trips of less than 10 miles. Those trips have been long enough for the temp gauge to read 210. After changing the oil, it's between 45 & 50 on start up. When I first started it after changing the oil, it took a second or two for the gauge to come up. I couldn't figure out a way to put oil in the filter and not have it leak out when I was attaching it.

I'm taking my gauge readings with a grain of salt right now. The engine runs well with alittle tick/tap when it's first started. The other odd thing is that the original odo showed 248,000, so I know I should investigate to see if the engine was swapped at one point. What has me wondering if the engine has been replaced is that quite afew replacement parts are either Jeep or performance replacements (hotter accel coil, K&N air filter, exhaust is a factory replacement), so somebody was really taking care of this jeep at one point.
 
Last edited:
Not sure if your saying youve got coolant in the oil? Well if you have that obviously aint right and i see the point.
 
dagr8tim said:
I have a question about replacing the sender. Is there a different sender for 4.0's with the gauge versus the idiot light?

My XJ came with the idiot light cluster, and I swapped for a gauge cluster. When I started it, the starting pressure showed at 40 to 45 PSI on start up/short trips of less than 10 miles. Those trips have been long enough for the temp gauge to read 210. After changing the oil, it's between 45 & 50 on start up. When I first started it after changing the oil, it took a second or two for the gauge to come up. I couldn't figure out a way to put oil in the filter and not have it leak out when I was attaching it.

I'm taking my gauge readings with a grain of salt right now. The engine runs well with alittle tick/tap when it's first started. The other odd thing is that the original odo showed 248,000, so I know I should investigate to see if the engine was swapped at one point. What has me wondering if the engine has been replaced is that quite afew replacement parts are either Jeep or performance replacements (hotter accel coil, K&N air filter, exhaust is a factory replacement), so somebody was really taking care of this jeep at one point.
Click to expand...

I believe the idiot lights are simple on/off senders where the gauges use a variable sender.
 
dunbad said:
Not sure if your saying youve got coolant in the oil? Well if you have that obviously aint right and i see the point.
Click to expand...

I'm sorry to be more clear, it had coolant in the oil when i bought it 0331 head cracked enough said.

After the new head i haven't seen any coolant in the oil but I wasn't sure if i should be concerned with the lower than normal pressure.

Hope thats a little more clear.
 
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