Tribal4x4 said:
i usually use valvoline high mileage 10w40 with a fram filter. i have noticed that it does it at idle or when i slow down. when i have my foot on the throttle, it is right around 40psi. i dont really drive it hard either. well not in the last year or so. i will change my oil this weekend and move up to like 20w50 or so and check that plug for the sending unit. if that doesnt work i will pull the pan and check the oil pump screeen. and then...( yes theres more) if that doesnt work then i guess its time for a rebuild or possibly a small deisel swap( heh heh heh)
Jeeps minimum factory spec for oil pressure for the 4.0 is 13 psi :shiver:. So if you still have 20 psi at hot idle, and a good pressure gauge and sensor than you are still OK. Sounds like your gauge and sensor is working if your getting 40 psi cold and higher rpms, and 20 psi at hot idle with a used engine, most gauge failures read zero or over 80 psi.
But if you are like me and have trouble sleeping at night think of your poor 4.0 having such low oil pressure, the fix is easy. I run 20W50 plus a quart of Lucas oil additive in the summer in mine. And then just 20W50 in the winter. I have 248,000 miles, and I get 22 psi hot idle, 30-40 psi hot cruizing, and 60 psi at cold engine start up.
I had only 10 lbs of oil pressure one day when I freaked out and stop using 10W30 and Fram filters. If you are in a real hot climate where cold weather starts are not an issue, you might try straight 40 wt, or 70%/30% blend of straight 40/50 wt. I am actually thinking of going back to single viscosity oil this summer and trying about 4 quarts of 40 wt with 2 quarts of 50 wt here in Houston, to see if the oil pressure is more or less stable from hot to cold operation than the 20W50. An ex-mechanic from a Chrysler Jeep dealership here suggested it to me yesterday, and I had already been considering it.
I am starting to think there is a problem with the polymers the oil companies are using now, a problem with viscosity loss under high shear in our engines at high temperatures that is contributing the low oil presures so many of us are seeing at hot idle oil pressure. They use some kind of synthetic polymers to get the multiviscosity effect, but I have read that they can break down over time from shear forces (and possibly oxidation?). Any way this ex Jeep dealership mechanic said the 4.0s would run forever on straight 40 wt dyno oil! That is of course with regular oil and filter changes.
We crossed paths at a muffler shop yesterday. He also told me that Chrysler has had a lot of problems for years now with cat converter warrantys, and that it was a Jeep factory defect. Hmm.
Unfortunatley it may be a very long time before that 4.0 dies and gets replaced with a diesel.
Oh, and get rid of the Valvoline, it is well known for sludge and wax
build up in engines. I use Exxon and Castrol :loveu:, and they are available in the 20W50 dyno oils.:sunshine: If I had a new engine I would probably use Mobil 1, 10W30 in it!
