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Oil Pressure Crazy

Jeff-97XJ

NAXJA Forum User
Location
Atlanta, GA
1997XJ, 4.0L, AW-4, 231J, 460K miles. Original Motor.
Oil pump changed at dealer at 250K as maintenance item.

When I start the XJ cold, she powers up pressure to 50 PSI.
After 10 minutes or so pressure gauge drops to 10 PSI.

Once hot, everytime I stop and turn of motor, when I turn it back on the check engine light comes on and the pressure is 0. after driving 30 seconds or so, the light goes off and the pressure goes up to 10 PSI.

I put in a new Chrysler oil sending unit and things were better for a couple of days and now back to 10 PSI.

I use 5-30 oil in my engine.

Any ideas what is problem?
 
460K miles is probably the main problem. So is 5w-30 weight oil during the summer.

Use 10w-40 or even 20w-50. The sending unit may be slightly off, another sender might read a few psi higher or lower.

10 psi is on the low side, and will likely trigger the warning lamp, but lots of 4.0 L owners have driven lots of miles with less than perfect oil pressure. Clean the wire plug connections at the sender.

10-20 psi at warm idle and 30-50 psi at 50 mph would be normal.
 
Sort of related, I'm having to use Lucas Oil stabilizer to get my hot idle up a bit. On my next oil change, I'm considering changing from 10w-30 to 5w-40. Thought being I have some piston slap until it warms up, and have read too much viscosity at startup can exacerbate the piston slap, but want 40 at hot to help the hot idle.

Thoughts?
 
I recommend the 15w40 Rotella. Rotella still has ZDDP in it for the cam wear. Otherwise I recommend adding ZDDP with each oil change.
 
I've read that recommendation (and the maelstrom of opinions about ZDDP etc), but isn't 15 a bit thick on the cold side?

Also, I thought Rotella phased out the high ZDDP some years ago.
 
Conventional 15w-40 in Austin will be no problem year round.

Synthetic 5w-40 is a good viscosity for year round use in the continental U.S.
 
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