Normal Oil Pressure for 4.0

MrBClark

MrBClark

TJ Enthusiast
Joined
Mar 30, 2019
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300
Location
Montoursville Pennsylvania
Ok I just kinda want to hear opinions on my Jeeps oil pressure. I have read around and it seems that it is fine, but just want to make sure.

Note: The head was cracked on my Jeep. I'm sure the OP isnt what it used to be, but I still dont think it's horrible.

I have posted a picture when the jeep had been run for like 40 mins. One at idle, and the other at 2k rpm. At idle it seems it dropped around 12-15. At 2k rpm, it is around 37-40. It was tough to take a pic so you probably cant see the one at 2k rpm all that well. Of course, when it starts cold it is much better, then it drops. When i start it up warm, it takes a bit for the OP to build up. The check gauges comes on for a few seconds. Then once i get going, it stays up there. It is always 40+ on the highway.

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I bought my 02 with 116k miles on it & was steady & just under 40 psi. A few months later it spun a rod bearing. I never saw the oil pressure drop, and even with the rod knocking, the oil pressure never dropped. But after I rebuilt the engine & up to now with like 2000 miles on it, the oil pressure is rock solid at just shy of 60 psi. RPMs will make it go up a little but not much.
 
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Airjunky said:
I bought my 02 with 116k miles on it & was steady & just under 40 psi. A few months later it spun a rod bearing. I never saw the oil pressure drop, and even with the rod knocking, the oil pressure never dropped. But after I rebuilt the engine & up to now with like 2000 miles on it, the oil pressure is rock solid at just shy of 60 psi. RPMs will make it go up a little but not much.
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If mine does something like that, I will fix it, but at this point, I want it to run for a very good bit of time. It has run great, it's just I know the bearings arent at factory level.
 
And just to state the obvious here, that factory oil pressure gauge is practically worthless. If you want to measure oil pressure accurately, you need to hook up an aftermarket oil pressure test gauge to it. Just putting this info out there (y)
 
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Chris said:
And just to state the obvious here, that factory oil pressure gauge is practically worthless. If you want to measure oil pressure accurately, you need to hook up an aftermarket oil pressure test gauge to it. Just putting this info out there (y)
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That explains why it just sits on 40 or so. The engine seems fine though
 
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Raymund said:
That explains why it just sits on 40 or so.
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The factory was forced to reprogram the oil pressure gauge sometime around 2002 to always read mid-scale so long as the real oil pressure is ok. Forced because the new TJ introduced in 1996 brought lots of new buyers who had never owned a vehicle that had an oil pressure gauge. Early TJ oil pressure gauges were accurate and they scared many new owners because the oil pressure indicator varied up and down as it was supposed to. They complained to the dealers who couldn't convince them it was normal. The dealers forced the factory to reprogram them to stay mid-scale so the owners wouldn't complain. Early TJ oil pressure gauges are accurate, newer gauges were just dumbed down. But so long as they're reading mid-scale the real underlying oil pressure is fine.
 
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Jerry Bransford said:
The factory was forced to reprogram the oil pressure gauge sometime around 2001 to always read mid-scale so long as the real oil pressure is ok. Forced because the new TJ introduced in 1996 brought lots of new buyers who had never owned a vehicle that had an oil pressure gauge. Early TJ oil pressure gauges were accurate and they scared many new owners because the oil pressure indicator varied up and down as it was supposed to. They complained to the dealers who couldn't convince them it was normal. The dealers forced the factory to reprogram them to stay mid-scale so the owners wouldn't complain. Early TJ oil pressure gauges are accurate, newer gauges were just dumbed down. But so long as they're reading mid-scale the real underlying oil pressure is fine.
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Thanks for that info. The only time it moved was when it needed a new oil pressure sensor and the old check engine light said hello.
The wealth of knowledge here is impressive as well as the willingness to share it. 👍
 
Thanks Jerry for the explanation. I have a 2006 TJ with 4.0, and the guage will show a good bit over 40, like 50-55 only when I first start it up in the morning, when cold. After it's warmed up it will stay a little over 40 no matter what, high speed. low speed, idle. Doesn't matter, it just stays put. I kinda figured that guage was more of an idiot light.
 
Jerry Bransford said:
The factory was forced to reprogram the oil pressure gauge sometime around 2001 to always read mid-scale so long as the real oil pressure is ok. Forced because the new TJ introduced in 1996 brought lots of new buyers who had never owned a vehicle that had an oil pressure gauge. Early TJ oil pressure gauges were accurate and they scared many new owners because the oil pressure indicator varied up and down as it was supposed to. They complained to the dealers who couldn't convince them it was normal. The dealers forced the factory to reprogram them to stay mid-scale so the owners wouldn't complain. Early TJ oil pressure gauges are accurate, newer gauges were just dumbed down. But so long as they're reading mid-scale the real underlying oil pressure is fine.
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Yea mine is an 01 with an actual gauge. Not the one that always stays around 40
 
Hi Guys - New question on this topic. My 98’ TJ used to idle at 20psi and then go up to about 40psi with the temps before shifting. Recently it idles at 40psi and goes up to 60psi with the rpms. The dip says it’s in the safe zone. First question, is operating in the 40-60psi range okay or will I be breaking something soon. Second, any ideas what could cause it to now be operating at higher psi?
 
MossGreen98! said:
Hi Guys - New question on this topic. My 98’ TJ used to idle at 20psi and then go up to about 40psi with the temps before shifting. Recently it idles at 40psi and goes up to 60psi with the rpms. The dip says it’s in the safe zone. First question, is operating in the 40-60psi range okay or will I be breaking something soon. Second, any ideas what could cause it to now be operating at higher psi?
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From my understanding, that gauge isn’t very accurate. Mine always reads between 40-60psi. I don’t know why yours would have changed. Hopefully someone else will chime in.
 
The earlier years have accurate gauges. My '98 is bang on compared to a mechanical gauge.

MossGreen98! said:
Hi Guys - New question on this topic. My 98’ TJ used to idle at 20psi and then go up to about 40psi with the temps before shifting. Recently it idles at 40psi and goes up to 60psi with the rpms. The dip says it’s in the safe zone. First question, is operating in the 40-60psi range okay or will I be breaking something soon. Second, any ideas what could cause it to now be operating at higher psi?
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Totally normal pressures. Pressure relief valve on the pump is 72psi IIRC. You don't have to worry about hurting your motor because too much oil pressure. Also, it has no correlation to your oil level---well, almost no correlation. The only way oil level will affect pressure is if you don't have enough and you suck air. Then we will be talking about how to rebuild your engine. The increased pressure likely has to do with cooler weather. I'll bet if you drive it longer/harder it'll be back towards what you were seeing before.

**Edit-- you said:

MossGreen98! said:
Hi Guys - My 98’ TJ used to idle at 20psi and then go up to about 40psi with the temps before shifting.
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Where you said temps, did you mean revs? Your oil pressure will be very high in the first few minutes of cold start up then drop as the oil gets warmer.
 
JMT said:
From my understanding, that gauge isn’t very accurate.
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It is on his '98 TJ, early TJs had "real" oil pressure gauges that showed the true oil pressure. The oil pressure gauge was reprogrammed later, 2000-2001 or so, to only show a mid-scale reading because the real varying oil pressures were scaring too many new owners of TJs. Their dealers couldn't convince them the oil pressure was supposed to vary up and down in step with the engine rpms.
 
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Jerry Bransford said:
It is on his '98 TJ, early TJs had "real" oil pressure gauges that showed the true oil pressure. The oil pressure gauge was reprogrammed later, 2000-2001 or so, to only show a mid-scale reading because the real varying oil pressures were scaring too many new owners of TJs. Their dealers couldn't convince them the oil pressure was supposed to vary up and down in step with the engine rpms.
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Thanks. I wouldn't mind a real gauge!
 
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Jerry Bransford said:
It is on his '98 TJ, early TJs had "real" oil pressure gauges that showed the true oil pressure. The oil pressure gauge was reprogrammed later, 2000-2001 or so, to only show a mid-scale reading because the real varying oil pressures were scaring too many new owners of TJs. Their dealers couldn't convince them the oil pressure was supposed to vary up and down in step with the engine rpms.
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My first Jeep was a ‘97 TJ, oil pressure above 40 has been good, if it drops below it’s time for a new filter. I just bought an ‘06 LJR, and it also runs above 40, but apparently that’s the firmware, not the actual reading? Haven’t had it long enough to need a new filter. Is there a way to make the gauge accurate?
 
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