I have a 98 xj with 150k, and I changed the oil in it today. Before, I had 45-50psi at cold start. About 25-35 at hot idle. I changed to 5w30 valvoline max life synthetic blend and a mopar filter. Now,I have the same cold start oil pressure. But, I let it warm up and it has 35-40, but when it's fully hot (Highway driving) and I come to a stop, it had anywhere from 12-20 psi. When I touch the gas pedal, it rises to 40. It seems like the gauge has a huge delay. I haven't verified with a mechanical gauge. Any input is extremely appreciated. Thanks!

 

What type and weight oil did you previously run?

 

I just bought it 2 weeks ago from a dealer, no clue

 

It probably had thicker oil in it before. As for the delayed reading, I've read that these are somewhat prone to clogging where the gauge is screwed in. I think the easiest, tho messy way, to clear it is to start it briefly with the sender out. Then make sure the sender is clean too. Might be a better way, I've never done it.

 

Is it normal to have around 12psi at hot idle?

 

"Normal" as in a lot of people experience it, yes.

Technically a dealer is supposed to fix engines with less than 13 PSI at hot idle, as checked by a test gauge. If you're looking at the dash you may not actually have 12 PSI lol

A lot of factors influence oil pressure: bearing wear, pump wear, oil filter, oil viscosity, oil temp, busted sending unit, poor wiring.

If your engine isn't making bad noises and oil still makes it up under the valve cover I wouldn't worry. Take care of easy things though. Most of Jeep ownership is maintenance.

 

I read somewhere you can put a t-fitting on the stock sending unit and use a mechanical gauge inside the Jeep. Is that possible?

 

Mechanical oil pressure gauge from T fitting to inside the Jeep, yes its possible.
Practical, has risk. What if the line fails and leaks, how fast will that oil spray make a mess.
This is the purpose of a sending unit, no fluid line into the compartment.
Would you consider a cowl mount gauge, any possible leak is still outside the compartment.

 

Dealer probably put some thick oil in there to show a high pressure and now you are seeing the real pressure.

 

High pressure is resistance to flow.

That's not a good thing.

 

I just went for a drive in it. Warm idle is 23, hot is 15. If the a/c kicks on, it goes to about 13 with the drop in rpm. If I raise the rpm to anything over idle, it goes right up to 40.
Think I'm alright?

 

VERIFY the pressure with a rented mechanical gauge. Did you whack the oil pressure sending unit when removing the filter?

 

This man knows what he is talking about
This man knows what he is talking about
That oil type flows easier than 10-40 dino which means a little lower pressure