1998 Cherokee 4.0
Oil pressure is fine when it is first started up and sits at about half when driving at about 2,000rpm doesnt go much past that. drops down to the 1st or second line at idle when warm.
only has 130,000kms
any ideas bad pump or faulty sending unit?
i dont think that its a clearance issue with such low KMS

 

I used to have low oil pressure woes and I have done a lot to fight it.

First I siwtched to Rotella 15/40 engine oil. Better for our Flat tappet motors anyway.

Slightly better oil pressure

Then I removed the Valve Cover, and oil pan and commenced to cleaning all the crude out.

No real Changee in Pressure.

In the progress I fixed all my oil leaks.

Slight increase but gradually went back to nothing.

Then I changed out the sender. I did get my highest increase in pressure by like yours once it warmed up good it would start to go back down.

Last and finally I went to a high flow oil pump. OMG what a difference. I run 60 PSI at start up now and then once it warms up it is at a constant 40 PSI.

If that didn't fix it I was gonna start replacing the Bearings on the engine. But I was able to get the Oil Pressure up with a new pump.

 

first thing to do is to get a manual oil pressure gauge and put on it to see what you actually have for oil pressure. it could be as simple as a bad sending unit reading improperly.
if you put a manual gauge on it to test it with and it verifies low oil pressure then it could be quite a few different things.

 

same thing with my xj... i started to run heavier oil which did help but still after it warms up it does drop to the second line. a mechanic friend of mine told me (dont know how much truth there is in this as he's a chevy guy) that dodge (jeep included) are notorious for "lazy oil pumps" and he may be right as my dakota is the same way.. so as Stryker said, get a new pump and it should fix the problem for ya but in the meantime just run a heavier oil and that will help.

 

How much did that high flow oil pump run you?

 

If the pump is lazy I wouldnt run anything heavier thru it and it dont help that much its just harder on the pump think about it.

 

That sounds pretty normal to me. When hot you should idle at about 20psi, which is the 1/4 marker on the gauge, or the second line. As low as 15psi is OK. At 2000RPMs 40PSI sounds about right too.

 

the rule is there should be at least 10psi per every 1k rpm.. pressure and flow are 2 different things.. u have too much pressure you wont necessarily have enough flow..

 

il check the pressure manualy this week, thanks for the help

 

I think it was about 100 bucks.

 

Amen. Flow rules.