Oil pressure on 4.0

BrunoPizz97

BrunoPizz97

TJ Enthusiast
Joined
Jul 11, 2019
Messages
408
Location
Long Island
Hey guys,
Been a while since I have posted, mainly because Ive had minimal issues with the jeep ... Knock on wood...

But im back and for obvious reasons.... I have an issue or I have a concern and would like to prevent an issue.

On my 97 Wrangler at idle oil pressure reads about 15 ish PSI and at crusing speeds it reads just shy of 40 PSI i would say about 5 - 10 psi variance because it fluctuates.

Now it wasnt shy of 40 PSI a few months ago and it would always read 40 when I would be doing any kind of driving.

Im not sure if I should be concerned. is my oil sending unit going bad or is it just a faulty sensor?

The motor runs flawlessly ... Knock on wood....
No ticking or knocking at all and always turns over on the first try.

If anyone has a solution it would be much appreciated
 
BrunoPizz97 said:
Hey guys,
Been a while since I have posted, mainly because Ive had minimal issues with the jeep ... Knock on wood...

But im back and for obvious reasons.... I have an issue or I have a concern and would like to prevent an issue.

On my 97 Wrangler at idle oil pressure reads about 15 ish PSI and at crusing speeds it reads just shy of 40 PSI i would say about 5 - 10 psi variance because it fluctuates.

Now it wasnt shy of 40 PSI a few months ago and it would always read 40 when I would be doing any kind of driving.
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A varying oil pressure is absolutely 100% normal, and the oil pressure gauge on your '97 was designed to show that varying oil pressure. The oil pressure varies because the oil pump is engine-driven so the oil pressure will definitely vary in direct step with the engine rpms. A good rule-of-thumb for acceptable oil pressure is 10 psi per thousand engine rpms.

Your would not have stayed at 40 psi all the time no matter what the engine rpms are. Varying engine rpms are absolutely 100% normal and to be expected.

Only on newer TJs was the oil pressure gauge reprogrammed to no longer show the true varying oil pressure which was scaring some new TJ owners who had never had a real oil pressure gauge before. For newer TJs it does show a continuous 40 psi or so but it's not the real varying underlying oil pressure.
 
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Jerry Bransford said:
A varying oil pressure is absolutely 100% normal, and the oil pressure gauge on your '97 was designed to show that varying oil pressure. The oil pressure varies because the oil pump is engine-driven so the oil pressure will definitely vary in direct step with the engine rpms. A good rule-of-thumb for acceptable oil pressure is 10 psi per thousand engine rpms.

Your would not have stayed at 40 psi all the time no matter what the engine rpms are. Varying engine rpms are absolutely 100% normal and to be expected.

Only on newer TJs was the oil pressure gauge reprogrammed to no longer show the true varying oil pressure which was scaring some new TJ owners who had never had a real oil pressure gauge before. For newer TJs it does show a continuous 40 psi or so but it's not the real varying underlying oil pressure.
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This i am completely aware of with the programming of the oil gauge on newer Tjs. I just thought it was odd since the 4 Years of ownership I haven't seen the oil pressure go below 40 PSI while driving. so I just wanted some input. if you think that this is normal then ill leave it be. And i did not know that the oil pump was engine driven, so basically what this means is that the oil pump wouldnt have any issues. If this is incorrect please correct me!

Thank you
 
BrunoPizz97 said:
This i am completely aware of with the programming of the oil gauge on newer Tjs. I just thought it was odd since the 4 Years of ownership I haven't seen the oil pressure go below 40 PSI while driving. so I just wanted some input. if you think that this is normal then ill leave it be.
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I believe you were mis-remembering it staying at 40 psi at all rpms which would not be normal for a '97.
 
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If you remember it staying at 40, then your oil pressure sensor is not working properly. Maybe it's working properly now, maybe it's not. For peace of mind, go pick up a Mopar unit (not aftermarket; they don't work reliably).
 
bromel said:
If you remember it staying at 40, then your oil pressure sensor is not working properly. Maybe it's working properly now, maybe it's not. For peace of mind, go pick up a Mopar unit (not aftermarket; they don't work reliably).
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Hello Fellow New Yorker, Lol
Yeah I am not sure where Jerry was insinuating. kinda need a more clearer direction with his response.
But I will swap out the Sensor for a new Mopar one. It seems odd for it to be reading differently that it was been in the past.
 
Moglocker said:
What about our 2002 sport,is it a (fauxe) oil gauge too,thanks jerry
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2002 is a real gauge. 2003 started the dummy gauge. If you read the 2002 and 2003 FSMs, the description of operation of the gauge is different.

2002 is linear, 2003 keeps it in the normal range for anything beyond 3 psi on the 2.4 and 6 psi on the 4.0. You will get a low oil pressure warning if you dip below the 6 psi. There is no high pressure warning and the gauge does not ever go into "high" either. But there are physical blowoffs in the oil pump that prevent engine damage due to too-high oil pressure.
 
BrunoPizz97 said:
I guess my jeep is just slightly special then 😂
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Maybe you didn't pay as much attention as you think. They can sit "around 40" a lot of the time but a 97 should definitely be moving up/down some. It should not all of a sudden be sitting at 15 psi when it's lived it's whole life close to 40 though. If that is the case then you probably have a bad sending unit.
 
machoheadgames said:
Maybe you didn't pay as much attention as you think. They can sit "around 40" a lot of the time but a 97 should definitely be moving up/down some. It should not all of a sudden be sitting at 15 psi when it's lived it's whole life close to 40 though. If that is the case then you probably have a bad sending unit.
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So when idling or lets say when i first start it up. Oil pressure is good then itll warm up and have pressure at 15 PSI itll fluctuate but it wont jump to 40 then to 15 at idle.

So idle is at 15 ish PSI

When driving ( a couple of months ago) the gauge would read 40 PSI when driving...
lets say i come to a red light it would drop down to 15 PSI or somewhere close or it would just fluctuate between 15 and 40.
Green light .... goes back to 40.

NOW
still fluctuates, but when driving its just shy of 40
gets to red light goes to 15 or fluctuates....

Green light and is just shy of 40 PSI
 
My 99 4.0 always varied from brand new. It has gradually lost maybe 5 lbs of pressure, both low and high after 200K. I DID have my gauge start acting weird 10 years or so ago and a new sending unit had it corrected. You might want to consider changing out the unit and/or put a temporary mechanical gauge in to check that all is well. As Jerry stated 10 lbs of oil pressure per 1K of RPM is typically considered the norm and everything is happy with that.
 
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BrunoPizz97 said:
So when idling or lets say when i first start it up. Oil pressure is good then itll warm up and have pressure at 15 PSI itll fluctuate but it wont jump to 40 then to 15 at idle.

So idle is at 15 ish PSI

When driving ( a couple of months ago) the gauge would read 40 PSI when driving...
lets say i come to a red light it would drop down to 15 PSI or somewhere close or it would just fluctuate between 15 and 40.
Green light .... goes back to 40.

NOW
still fluctuates, but when driving its just shy of 40
gets to red light goes to 15 or fluctuates....

Green light and is just shy of 40 PSI
Click to expand...
It's your wallet, but I'd probably throw a new Mopar oil pressure switch/sender at it. Worst case it doesn't help and you have a spare for the day your current one does die which at that age could be whenever.

I would not worry about actual issues though. Typically oil problems are all or nothing. Usually if you have any pressure really at all, you're good. Usually actual issues are true 0 psi cases where the oil pump pickup is starved or you lost all your oil or whatever else. If you've got 15 psi at idle then you've got enough, which is really all that matters. I think the root issue though is your sender getting finicky.
 
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