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wtf, oil pressure again

R

rehab

NAXJA Forum User
Location
The Citadel, SC
i have a 4.2 with 4.0 HO head and it has been runing great.

but today driving to work, i stoped at a light and the oil psi went from 30 - dead zero. so i'm like ok, wtf? then when accelerating it bumped back up to 30 and stayed there while crusing at 55. now i changed the oil, 10w 30, and added a mobile one filter, with a lucus addative for bumping up the oil pressure. now i am still at 20 psi when idleing, but here is the catch, it only happens when the engine gets to runing temp. when i first start it up its at 40 psi and holds strong.


i have gone through and checked the guages and sending unit with a new mechanical guage and they both read the same reading, 20 psi at idle when warming up. I havent had a chance to drive it yet with the new oil and filter but i am suspecting the same result as before. what do you guys think?

is it ok to continue running the jeep with 20 psi? I have no clue other than the oil pump, as to what could cause this.
 
13psi at a hot idle is factory spec.
 
I have a stock 4.0 in my 2000 cherokee and had the same problem with my gauge dropping to zero at idle. After trying lucas and checking if the motor was properly grounded, I checked all wiring connections making sure no dirt fouled any contacts, then removed the oil pressure sensor (oil pressure interupter switch "?") to check for blockage and thoroughly cleaned out the sensor and reinstalled it. I figured the sensor should last longer than seven years but I was ultimatly wrong since the problem remained until I gave in to paying the $46.99 for a new sensor at autozone and problem solved!
 
Last edited:
rehab said:
i have a 4.2 with 4.0 HO head and it has been runing great.

but today driving to work, i stoped at a light and the oil psi went from 30 - dead zero. so i'm like ok, wtf? then when accelerating it bumped back up to 30 and stayed there while crusing at 55. now i changed the oil, 10w 30, and added a mobile one filter, with a lucus addative for bumping up the oil pressure. now i am still at 20 psi when idleing, but here is the catch, it only happens when the engine gets to runing temp. when i first start it up its at 40 psi and holds strong.


i have gone through and checked the guages and sending unit with a new mechanical guage and they both read the same reading, 20 psi at idle when warming up. I havent had a chance to drive it yet with the new oil and filter but i am suspecting the same result as before. what do you guys think?

is it ok to continue running the jeep with 20 psi? I have no clue other than the oil pump, as to what could cause this.
Click to expand...

Since you have verified that the 20 psi reading is actually 20 psi, at idle, you are just fine. The FSM says 13 psi at idle is OK, and the idiot lights are apparently set even lower than 13 psi. As long as it holds 20 psi at idle and goes back to 30 psi or more at cruising speed you are fine.

On the ticking problem try adding a pint of Marvel mystery oil with the Lucas, the combo of the two did wonders for ticking. The MMO might drop you oil a pressure about 1 psi at first, but don't worry 19 is still OK.
 
PornstaR said:
I have had multiple sending units fail...... going with a OEM one now to see if it lasts more than a month or so
Click to expand...
I've gone through about 5 sending units and found that one off an 88 xj (renix style) worked better and lasted longer.

after driving it around last night it seemed to be holding pressure a lot better and not droping down as low.

thanks for the help guys.
 
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