Low Oil Pressure Advice Jeep 4.0

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6
Hi all, Recently purchased an '01 Cherokee with the 4.0. Once I got it home I found out it had the cracked 0331 head. I've replaced the head with an aftermarket replacement. The jeep has 140k miles on it, no knocking, ticks, engine noise etc. It does however have low idle oil pressure when hot verified with a mechanical gauge. (5-8 PSI at idle. 20-35 while at cruising speeds). Even at idle with the low oil pressure all of the rockers are receiving oil and everything sounds pretty quiet. I know there are many posts on many forums about the same issue, just looking for advice until I can decide to sell the car, rebuild it. or drive it till something blows. I know that oil selection alone will not replace engine tolerances or fix damage already done by the coolant/oil contamination. Just looking to buy some time and maybe bump the oil pressure a bit to keep the 'check gauge' light from coming on when the car is idling in traffic. I am currently running a Napa Gold Oil filter stock size, and PYB 10w30. I'm looking to go up a grade in weight to a 40w if possible, not overly concerned about extended oil changes, and cold weather starts aren't a problem as I am in South Carolina and we only get a few days a year of below freezing mornings. Do I: ? 1. Leave the 10w30 PYB in, and drive it with the low hot idle pressure? (oil pressure does not equal flow debate) 2. Bump up to a thicker HM 30w oil like M1 HM which seems to be a thicker 30w when compared to PYB? Would I even notice this change? ([email protected] value of 12.1 vs 10.5) 3. Bump to a 40w HDEO oil like Rotella T6 5w40 or M1 TDT 5w40? These types of oil seem to get alot of praise for the 4.0 with or without oil pressure problems. Not too concerned about spending a few more bucks on these even if i'm not using them to their full OCI potential. 4. Some other combination/oil not mentioned? Would a larger oil filter like a wix 51515 help? How about mixing weights to get something not as thick as say a 40w but thicker than my PYB 10w30? (I have read some previous posts where a thick 40w caused engine knocks and ticks that weren't present before changing to the thicker oil) Thanks!
 
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3,275
Location
On another site
First, welcome What about a new oil pump? If the old one has excessive wear from the 0331 situation, that may be the only issue. How's the pressure cold?
 

Carnut123

Thread starter
Messages
6
I did pull the pan to check the pump and pickup screen and both looked new. I'm assuming the previous owner had the pump replaced chasing the low oil pressure issue. (not knowing the head was cracked and leaking coolant into the oil). Cold pressure on startup is 45-50.
 
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4,059
Location
Chicago, IL
it's possible that you have encountered some bearing wear. not sure why, but when I had my 1989 4.0, I got low oil pressure around 125k miles. I had always changed the oil every 3k miles and drive it conservatively. ended up rebuilding the engine and driving for another 50k until rust took it away. no harm in running a 15w-40
 
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13,194
Location
Maricopa Arizona
My FIL toasted his 4.0 with coolant in the oil it took close to a year but he finally did it. Replaced it with a lower mileage 4.0 until he toasted thr transmission. Likely you need a rebuild but a higher grade such as 40 will give you about 10 PSI hot idle PSI.
 
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2,714
Location
PA
Isn't most 10w30 thinner at hot idle than 5w30 or 0w30...? I would switch to a Xw40 or even try running some 5w50
 
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2,499
Location
South Carolina
Since you have already R/R the oil pan the long term solution is: Water in oil = replacement of rod and main bearings. I would replace the oil pump while you have the pan off. This engine is perfectly happy with the factory recommended 10w-30.
 
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13,194
Location
Maricopa Arizona
Originally Posted by Warstud
I don't know what people think there going to solve by using thicker oil other than getting the numbers up.
There is a specified minimum to keep parts separated. IRC for a 4.0 Chrysler the minimum is around 13PSI. If the OP can obtain this with a higher grade good. Ideally the engine will be replaced.
 

Carnut123

Thread starter
Messages
6
Thanks for all the replies! I know the damage is already done to the bearings. Was just looking for some guidance on bumping the idle pressure a few psi to keep the check gauge light from bouncing off and on while I figure out if I want to rebuild or sell. I'll give one of the 40w recommendations a shot. Most likely the T6 , TDT, or Delo as they are all available locally at Wallyworld.
 
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22,874
Location
Apple Valley, California
Originally Posted by ka9mnx
Since you have already R/R the oil pan the long term solution is: Water in oil = replacement of rod and main bearings. I would replace the oil pump while you have the pan off. This engine is perfectly happy with the factory recommended 10w-30.
The cam bearings can't be done in the car. Those are what causes low oil pressure in these engines when it ingests coolant.
 
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25,050
Location
ON, Canada eh?
As a short term solution I would use a thicker weight oil like a 40wt / 50wt being in South Carolina. I would check the pump first and pressure relief valve to be sure it's in good condition and if it is then I would look at the bearings. Do not continue to drive it with low oil pressure using a 10w30 as this won't end well.
 
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Messages
26,085
Location
Upstate NY
This is the engine and year that has had engine issues with cracking piston skirts causing catastrophic engine failure. Ask me how I know.
 
Messages
2,499
Location
South Carolina
Originally Posted by Chris142
Originally Posted by ka9mnx
Since you have already R/R the oil pan the long term solution is: Water in oil = replacement of rod and main bearings. I would replace the oil pump while you have the pan off. This engine is perfectly happy with the factory recommended 10w-30.
The cam bearings can't be done in the car. Those are what causes low oil pressure in these engines when it ingests coolant.
I doubt the cam bearings are that bad. Rod and mains go first in this case.
 
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10,970
Location
Cincinnati, OH, USA
I've been running MaxLife red (actually NextGen green) bottle 10W40 in my ‘98 XJ for the past 15K, it has helped with both the slow RMS leak & hot oil pressure, there seems to be no trouble starting in sub-freezing weather. Both 5W30 & 10W30 didn't give enough oil pressure, and the engine went through both a LOT faster than 10W40. Need to remember the 4.0 is basically an old school AMC design-guess what the most common multigrade oil was in the day? 10W40!
 
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