I have a 1989 jeep Cherokee with the 4.0L and 186,000 miles. Recently i had the oil pan of to replace the rear main, and the oil pan gasket, and i thought that it would be a good idea to replace the oil pump while i was at it, i mean its a old jeep, and oil pumps are cheap, and plus my stock oil pressure gauge didn't work so i just went ahead and did it. So i went and changed it, and got a oil pressure gauge, and i was only getting about 10 psi at idle, and just about 20 psi when hot (100 degrees outside) when i started it cold i got around 40. Well, i talked this over with a mechanic, and he said the oil pump was bad. So i went and took it apart again, and replaced the oil pump again, and i also replaced the oil pickup tube. So i put it all back together and when i start it cold i get around 50 psi of oil pressure, but as soon as it heats up at idle i get around 10 psi, and driving its averages 20. I am using 10w-40, and i looked on alldata.com and it recomends 20w-50.... is it my oil thats causing me to have low oil pressure or is it normal, or is it because my motor is crap? i just don't know what to think anymore. please help?

 

The manual says 13 at idle and 40-50 under load,what was your pressure before you made these changes?

 

you could have a bad oil pressure sensor. i had to same problem. changed my sensor and im runnin normal pressure now

 

I have no idea what it was before.... and i have a aftermarket mechanical gauge on it.

 

did you replace the oil sending unit? Its the sensor just above the oil filter adaptor.

 

I finally got my sensor working, with 5w-30 I'm getting 35 at idle and 60 under load.