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Old 08-19-2011, 06:57 PM   #1
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Normal oil pressure on 4.0?

At idle, when warmed up, the pressure looks to be around the first line iirc. This puts it at about 18-22 (I'll have to look again to see if it's slightly over or under, can't remember right now). What's normal for these, during normal driving it goes up past the middle line for sure, just making sure the idle is sufficient(granted the gauge is accurate)

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Old 08-19-2011, 08:53 PM   #2
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as long as it stays in the middle I dont see the problem, when wheeling it can go above half way pretty easily from my experience (Higher RPM). As long as its not at one end or the other it shoud be fine. should be in the range of 15-50 psi under normal operating conditions.

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Old 08-19-2011, 09:31 PM   #3
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I idle around 40 and up to 55 on the freeway
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Old 08-20-2011, 03:02 AM   #4
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My 99' with 153K when warm will idle at about 20PSI and when driving goes up to 40PSI. This is with synthetic oil. A good rule of thumb would be 10PSI per 1k RPM of the engine. This is normal for an older engine.
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Old 08-22-2011, 05:15 PM   #5
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I just bought an '02 and it runs around 50-55 at Hwy speeds. Please tell me that's normal.
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Old 08-22-2011, 06:32 PM   #6
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Rule of thumb is 10 PSI for every 1000 RPM.

Also keep in mind newer Jeeps use dummy gauges on both oil and coolant and will usually stay around the 50 mark no matter what, even though at idle it will be much lower.

Older jeeps like my 97 show truer values and the oil pressure gauge fluctuates with RPM. Though I don't know what the year cut off was for when they moved to the dummy gauges.
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Old 08-22-2011, 11:12 PM   #7
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Quote:
Originally Posted by freeskier View Post
Rule of thumb is 10 PSI for every 1000 RPM.

Also keep in mind newer Jeeps use dummy gauges on both oil and coolant and will usually stay around the 50 mark no matter what, even though at idle it will be much lower.

Older jeeps like my 97 show truer values and the oil pressure gauge fluctuates with RPM. Though I don't know what the year cut off was for when they moved to the dummy gauges.
My 99' has a "real" gauge.
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Old 08-22-2011, 11:50 PM   #8
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Quote:
Originally Posted by freeskier
Rule of thumb is 10 PSI for every 1000 RPM.

Also keep in mind newer Jeeps use dummy gauges on both oil and coolant and will usually stay around the 50 mark no matter what, even though at idle it will be much lower.

Older jeeps like my 97 show truer values and the oil pressure gauge fluctuates with RPM. Though I don't know what the year cut off was for when they moved to the dummy gauges.
Can you expand on the dummy guage?
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Old 08-23-2011, 01:31 AM   #9
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Quote:
Originally Posted by MikeMTJ

Can you expand on the dummy guage?
Dummy gauges just show highs and lows of psi. People who were mechanically disinclined thought something was wrong when the gauge would fluctuate so they started using these dummy gauges instead.
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Old 08-23-2011, 01:43 AM   #10
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Can you expand on the dummy guage?
Customers were just complaning to the dealers saying the there car is not running right with like a 10 lb oil pressure Thinking thats not righon the older models which is completly normal at the normal temp so they put dummy guages in to stop the complaining. As long as your oil pressure goes up when drivng you should be fine. Maybe a problem if its at 0 of course either the guage or the motor but when there is a true low pressure you will hear some kind of knock.
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Old 08-23-2011, 08:51 AM   #11
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^^^^Yep.
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Old 08-23-2011, 11:35 AM   #12
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Cool! Thanks guys.
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Old 08-23-2011, 11:45 AM   #13
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Old 08-23-2011, 12:17 PM   #14
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Quote:
Originally Posted by Baltimore View Post
Customers were just complaning to the dealers saying the there car is not running right with like a 10 lb oil pressure Thinking thats not righon the older models which is completly normal at the normal temp so they put dummy guages in to stop the complaining. As long as your oil pressure goes up when drivng you should be fine. Maybe a problem if its at 0 of course either the guage or the motor but when there is a true low pressure you will hear some kind of knock.
yup, I don't remember all the specifics, but the newer models have a dummy gauge that reads 40psi almost all the time. Jeep turned the oil pressure sensor into a binary - it only knows if its above or below 3psi. So basically a CEL is only tripped, and the gauge only changes if oil pressure has been below 3psi for like 2 minutes or something...otherwise you see 40psi no matter what true oil pressure is.

there was a write up on JF a few years ago on changing out the 3psi binary sensor for an 8 psi binary sensor...at least giving you some time to pull over, but you can't go backwards to a real sensor....unless of course you use a seperate aftermarket gauge.
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Old 08-23-2011, 12:46 PM   #15
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Good info. I didn't know that about the dummy gauge. I guess that's what my 04 does as the needle sits just over the half-way mark until the motor is off.
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Old 08-24-2011, 07:59 PM   #16
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Originally Posted by MikeMTJ View Post
Can you expand on the dummy guage?
Manufacturers have also installed dummy coolant temperature gauges on numerous vehicles nowadays as well. On those, when the coolant temp is anywhere between 160-220^ or so (for example), the needle will remain pointed at one specific spot on the gauge. By the time the needle climbs at all above normal, the car is truly running hot... and you have precious little time to react. I hope you scan your gauges regularly while you drive.

Dummy coolant temp gauges are used for same reason dummy oil pressure gauges are used. Both temp and oil pressure will vary as the car is driven, which means the needles will constantly move on smart gauges. Dumb drivers, however, see the needle rise and/or fall and think something must be wrong, so they bring the car to the dealership to be fixed. When the shop says everything is operating as designed, the customers get disgruntled... so they call the manufacturer to complain about how the dealership cannot fix their car which is obviously broken.

After enough complaints, the manufacturer decided to lower the gauge intelligence to match that of the drivers. Problem solved. (Though it sucks for those of us who want our gauges to provide accurate information to us.)

When your oil pressure drops below the dummy gauge threshold, two things happen: the needle falls to zero (of course), and a warning light illuminates to catch your attention. Compare that to a car with no oil pressure gauge at all: when that car's oil pressure drops below the 'safe' threshold, a warning light illuminates to catch your attention. So in other words, a dummy gauge provides NO additional information over a simple warning light (aka 'an idiot light'). Is it any wonder why manufacturers have phased out oil pressure gauges (and even coolant temp gauges) on so many modern vehicles?
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Old 08-24-2011, 11:27 PM   #17
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My 2000 TJ has a real oil pressure gauge which fluctuates with RPM's. Must be after 2000 when they switched...
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Old 08-25-2011, 12:48 AM   #18
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my 2001 has true gauges. I can watch my oil pressure rise with rpm.
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Old 08-25-2011, 01:07 AM   #19
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WOW! I just learned something. Wonder what kinda gauges I have in the 2003 4.0? I've only had it a couple weeks, I know what I'll be checking out tomorrow.
Thanks for the info.
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Old 08-25-2011, 07:09 AM   #20
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Guess my '01 TJ has real gauges also then as it does flucuate with rpm's, although not very much.

Going off the top of my head, I'd say my oil pressure is between 40-45psi just about all the time. I think that's what that line is. Might could be 50-55 psi, but I think I'm remembering 40-45 as more like right.
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Old 08-25-2011, 10:28 AM   #21
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My 04 has the dummy so it was either 02 or 03 when they switched it.
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Old 08-25-2011, 10:56 AM   #22
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I'd have to guess 2000 was the last year with a "real" gauge. I have a late 2000 build year.

But yeah looks like I'm normal. Thanks guys
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Old 08-25-2011, 01:35 PM   #23
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my BMW has a "dummy" gauge and its oddly comforting

but i dont think its as bad as you guys describe - i tap in to the computer and i can see the true collant temperature and it will start to move if the car gets too hot. I do like that under normal conditions it never moves - and the few times i see it move i know there is something wrong, so it can work both ways, and it gives plenty of time.
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Old 07-06-2012, 08:52 AM   #24
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along the same lines - on oil pressure

I've got a '97 wrangler - 4 cycl - and for the most part the oil pressure reads about 42. Twice in the last month, both times the car was idling at a long light, the pressure started to fluctuate, and then dropped with the warning light/buzzer going off. I tapped the gas and the pressure kicked back up. Now a lights I keep an eye on the pressure and if it starts to drop, tap the gas. When the car is actually moving, the pressure is steady at 42.

The mechanics reply was $500 to replace the oil pump, which he claims commonly goes on Jeeps. Any thoughts? Real problem, something going, or basically normal.

If there were just idiot lights, I wouldn't have notice anything, except for the two quick lights/buzzer.
thanks in advance,
joe
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Old 07-06-2012, 02:35 PM   #25
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My 2005 sits in the middle, but climbs while under load so it cant be a total dummy guage.

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