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Unread 04-08-2013, 09:30 PM   #1
DJeepinOK
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Oil pressure Drops when idling?

I drive a 2000 TJ and changed the oil around 1k miles ago. I am running 10w-30 oil and I just recently noticed that after running for a while when the engine is nice and hot, the oil pressure drops from its norm to about 20 ish, but only when not pressing the gas. Now I'm not sure if this is normal or not because all the other threads are about it dropping to 0. So is this normal, and if not what should I look at first?

Also, my CEL has come on and off probably 5 times within the past few months. I know that the first time it came on I got it checked and it was the O2 sensor. Is this something that can fix itself and clear the error code?

Thanks!

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Unread 04-08-2013, 09:39 PM   #2
TravisHeim
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Mine does the same thing, probably drops a little lower than yours does. Its normal.
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Unread 04-08-2013, 10:04 PM   #3
Jon-joN
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Mechanical gauge or are you looking at the dummy meter on the Dash? If it's the dash meter then it's
Probably just the sensor going bad since all it does is give a solid reading as soon as it gets pressure. Now on a mechanical gauge, when warm, it should vary from 18-65 psi throughout the rpm range. Normally 40psi is the average but it depends on how your engine has worn over the years if it's higher or lower.
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Unread 04-08-2013, 10:20 PM   #4
TravisHeim
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Quote:
Originally Posted by Jon-joN View Post
Mechanical gauge or are you looking at the dummy meter on the Dash? If it's the dash meter then it's
Probably just the sensor going bad since all it does is give a solid reading as soon as it gets pressure. Now on a mechanical gauge, when warm, it should vary from 18-65 psi throughout the rpm range. Normally 40psi is the average but it depends on how your engine has worn over the years if it's higher or lower.
The dash oil pressure gauge's on my old 97 and now current 2000 both fluctuated with engine rpm, I don't think it's just a dummy gauge.
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Unread 04-08-2013, 10:35 PM   #5
tbburg
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Pressure drop at idle when hot is normal. 20(dash gauge) at idle and jumping up to 40-45 when you come off idle is normal operation.
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Unread 04-08-2013, 11:06 PM   #6
TJsjeeptj
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Mine does the same thing. It drops down to about the quarter mark at idle and goes back to half when the gas is pressed I'm not sure why either
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Unread 04-08-2013, 11:38 PM   #7
Knuckelhead
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Quote:
Originally Posted by TravisHeim View Post
The dash oil pressure gauge's on my old 97 and now current 2000 both fluctuated with engine rpm, I don't think it's just a dummy gauge.
It's not a dummy gauge. 20 psi at idle is normal.

IIRC 2003 went to the so called dummy gauge. Look here:
http://www.jeepforum.com/forum/f9/tj...gauge-1291693/

And here:
http://www.wranglerforum.com/f5/oil-...ot-144739.html
-Your mechanic is an idiot for telling you that. In reality, oil pressure is absolutely supposed to vary up and down in step with engine rpms. 20 psi at idle is very good, and heading up to 40-60 when accelerating is excellent, and the pressure dropping back down as the RPMs drop is 100% normal and to be expected too.

Your oil pressure is generated by a mechanical oil pump which spins faster and slower as the engine revs faster and slower. So naturally the oil pressure will go up and down in sync with the engine RPMs.

That the oil pressure does go up and down was unnecessarily alarming people who were new to "real" oil pressure gauges so the dealers were getting a lot of unnecessary complaints by people who didn't believe the dealer when they told them it was normal. So the dealers made the factory dumb the oil pressure gauge down in later model TJs so it only registers mid-scale so long as there is oil pressure. Dumb, that is not what oil pressure really does. That change happened around 2003 so your 2000 TJ is one of the fortunate models that show the real oil pressure.

So relax, your oil pressure is fine and you now know oil pressure is supposed to vary up and down in sync with the engine RPMs.-
...
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Unread 04-09-2013, 01:17 AM   #8
Necko2529
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Quote:
Originally Posted by Knuckelhead View Post
It's not a dummy gauge. 20 psi at idle is normal.

IIRC 2003 went to the so called dummy gauge. Look here:
http://www.jeepforum.com/forum/f9/tj...gauge-1291693/

And here:
http://www.wranglerforum.com/f5/oil-...ot-144739.html
-Your mechanic is an idiot for telling you that. In reality, oil pressure is absolutely supposed to vary up and down in step with engine rpms. 20 psi at idle is very good, and heading up to 40-60 when accelerating is excellent, and the pressure dropping back down as the RPMs drop is 100% normal and to be expected too.

Your oil pressure is generated by a mechanical oil pump which spins faster and slower as the engine revs faster and slower. So naturally the oil pressure will go up and down in sync with the engine RPMs.

That the oil pressure does go up and down was unnecessarily alarming people who were new to "real" oil pressure gauges so the dealers were getting a lot of unnecessary complaints by people who didn't believe the dealer when they told them it was normal. So the dealers made the factory dumb the oil pressure gauge down in later model TJs so it only registers mid-scale so long as there is oil pressure. Dumb, that is not what oil pressure really does. That change happened around 2003 so your 2000 TJ is one of the fortunate models that show the real oil pressure.

So relax, your oil pressure is fine and you now know oil pressure is supposed to vary up and down in sync with the engine RPMs.-
...
Yes, sir, you are correct.

It is 03+ that went with the dummy gauge. I remember my 01 TJ reading actual pressure so does my dads 94 ZJ and my 04 Freightliner Century...

03+ oil pressure gauge knows only Yes/No oil pressure and will remain in the same spot from when you first start it until you shut it off. I never know what the actual pressure is, it always sits in the sam spot.

What you are seeing is perfectly normal and it sounds like you have a healthy engine.

Knucklehead, if you get a thumbs down from me, i apologize. My phone acts dumb sometimes and selects random thongs if i flip the screen and make a selection. I try to cancel and then face you thumbs up.
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Unread 04-09-2013, 01:39 AM   #9
Knuckelhead
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Quote:
Originally Posted by Necko2529 View Post
Yes, sir, you are correct.

It is 03+ that went with the dummy gauge. I remember my 01 TJ reading actual pressure so does my dads 94 ZJ and my 04 Freightliner Century...

03+ oil pressure gauge knows only Yes/No oil pressure and will remain in the same spot from when you first start it until you shut it off. I never know what the actual pressure is, it always sits in the sam spot.

What you are seeing is perfectly normal and it sounds like you have a healthy engine.
I don't think it's a Yes/No function from the sending unit. IIRC when the oil pressure drops below 6 psi(?) you get a MIL light and the oil gauge drops to 0.
Quote:
Originally Posted by Necko2529 View Post

Knucklehead, if you get a thumbs down from me, i apologize. My phone acts dumb sometimes and selects random thongs if i flip the screen and make a selection. I try to cancel and then face you thumbs up.
All thumbs down get reviewed and your post will explain it...
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Unread 04-09-2013, 06:27 AM   #10
VBRubicon
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Quote:
Originally Posted by Necko2529 View Post
Knucklehead, if you get a thumbs down from me, i apologize. My phone acts dumb sometimes and selects random thongs if i flip the screen and make a selection. I try to cancel and then face you thumbs up.
If I were him, I'd be more worried about the random thongs you're picking out for him and not so much the thumbs down....

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Unread 04-09-2013, 07:15 AM   #11
DJeepinOK
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Ok thanks for the help!
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Unread 04-09-2013, 08:28 AM   #12
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Originally Posted by VBRubicon View Post
If I were him, I'd be more worried about the random thongs you're picking out for him and not so much the thumbs down....

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Unread 04-09-2013, 09:39 AM   #13
biffgnar
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Quote:
Originally Posted by Necko2529 View Post
03+ oil pressure gauge knows only Yes/No oil pressure and will remain in the same spot from when you first start it until you shut it off. I never know what the actual pressure is, it always sits in the sam spot.
While I accept that the gauge in my 06 is not an accurate reflection of pressure, the computer does at least move the needle around a bit on mine. Higher when cold and/or higher RPMs. Probably not the extent of the actual pressure fluctuations, but it doesn't sit in the same spot.
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Unread 04-09-2013, 11:59 AM   #14
Necko2529
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I need to start reading my posts before submitting....

But you guys get the point and no, not what i wrote but what i meant to write LOL.
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Unread 04-09-2013, 12:04 PM   #15
Necko2529
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Knucklehead, i think i read somewhere about oil psi threshold just can't remember where and what it was.

When i said Yes/No oil pressure, i was referring to the needle only showing L or just past the half mark no matter the engine temp.
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