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#1932012 - 06/23/10 07:19 PM Erratic oil pressure gauge
Jimmy9190 Offline


Registered: 02/17/07
Posts: 2971
Loc: Clermont, Florida
My factory oil pressure gauge is acting strange. When I start out in the morning it's fine, right up about 75-80 psi at 1800-2000 RPM. It will back down just a little to about 65-70 psi after I get going down the road 5 miles or so and hit operating temperature. It will stay there as long as I don't slow down for a period longer than 10 seconds (as in when I slow down in traffic on the interstate as I am driving to work) or if I have to stop for a red light.

When I do slow down or stop, the pressure drops toward the low end of the scale and then goes back up. But it does not go back to 65-70 psi, it is more in the middle around 50-55 psi. Sometimes it will stay at 50-55 psi and sometimes it will go back up to 70 psi as I increase RPM to 2000 and reach 70 mph cruising speed.

When I leave to come home from work, same thing happens. High pressure (normal pressure) till I stop at a light then it reads lower, around 50-55 psi at 1800 to 2000 RPM when going down the highway at 60-65 MPH.

I am thinking the oil pressure sending unit is not completely defective, but it is getting erratic since I have 130,600 miles on my truck now. It's the original gauge and sending unit.

I honestly don't think it's the bearings, the truck has good power, runs quiet and has a smooth idle and makes no odd noises. I appreciate any help or advice you can offer here. New sending unit is only $32.00 and easy to replace.

Thanks.
_________________________
Jimmy9190
2001 Dodge Dakota, 3.9 V6, 5-speed manual, 170K

"As long as you're in motion, you're moving in the right direction." - Ronnie Montrose


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#1932028 - 06/23/10 07:36 PM Re: Erratic oil pressure gauge [Re: Jimmy9190]
GMBoy Offline


Registered: 11/22/04
Posts: 6617
Loc: Texas
You don't say what vehicle this is, but in any event those oil pressures are not bad at all. Since the sender is a cheap and easy fix I say go for it. However, it could also be your oil pressure relief valve or even the oil filter. Change the oil and filter first and see what happens.

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#1932029 - 06/23/10 07:37 PM Re: Erratic oil pressure gauge [Re: Jimmy9190]
Warstud Offline


Registered: 09/02/05
Posts: 2661
Loc: MIchigan
That 75-80 psi seems high.

Here's mine which are normal:

55psi at startup (idle)
25 psi at operating temp (idle)
45-50 psi operating temp 2000 rpm

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#1932048 - 06/23/10 07:58 PM Re: Erratic oil pressure gauge [Re: Warstud]
cchase Offline


Registered: 11/03/09
Posts: 3971
Loc: New England
What you are describing sounds fairly typical of factory oil pressure gauge operation.

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#1932081 - 06/23/10 08:32 PM Re: Erratic oil pressure gauge [Re: cchase]
expat Offline


Registered: 05/12/09
Posts: 3750
Loc: Canada
It's Normal.
Engine oil pressure will drop as the engine warms up.

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#1932092 - 06/23/10 08:44 PM Re: Erratic oil pressure gauge [Re: expat]
jstutz Offline


Registered: 10/06/08
Posts: 1479
Loc: NC
We need to know what vehicle your driving.

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#1932207 - 06/23/10 10:19 PM Re: Erratic oil pressure gauge [Re: jstutz]
Jimmy9190 Offline


Registered: 02/17/07
Posts: 2971
Loc: Clermont, Florida
2001 Dodge Dakota. 3.9 liter V6 with a manual 5-speed. 130,500 miles on it now. Current oil fill is 4 quarts of Carquest store brand 10W30 conventional and a Napa Proselect oil filter. I have about 400 miles on the oil right now, just changed it 11 days ago.

Oil pressure gauge never acted like this before and I have owned this truck since December 2005 and have put over 90,000 miles on it. The gauge always was high till the engine got warm, then dropped a little but would always stay there while driving, whether I had slowed down or stopped did not matter. It would of course drop to about 40 psi on the gauge at idle, and still does when I stop at a light. This erratic operation of the gauge just started a week or maybe 10 days ago, which is why I think the sending unit is bad.
_________________________
Jimmy9190
2001 Dodge Dakota, 3.9 V6, 5-speed manual, 170K

"As long as you're in motion, you're moving in the right direction." - Ronnie Montrose


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#1932217 - 06/23/10 10:24 PM Re: Erratic oil pressure gauge [Re: Jimmy9190]
Gary Allan Offline


Registered: 09/28/02
Posts: 39806
Loc: Pottstown, PA
Yeah, but what you're describing isn't erratic. It's normal. Erratic would be if it was at a steady rpm ..which may be idle ..and have it jumping around for no good reason. Yours has good cause to go lower at lower rpm.
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http://lube-direct.com/gallan/

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#1932254 - 06/23/10 10:56 PM Re: Erratic oil pressure gauge [Re: Jimmy9190]
UncleS2 Offline


Registered: 05/27/02
Posts: 2998
Loc: Far North East Texas
Hmm...before you buy a new sending unit, you might want to ck the connections first. Still, a new SU is a pretty cheap fix.

PS- your OP gauge has *Numbers*? My 02 3.9 just has a few hash marks, unlabeled. I think of it as an idiot light, with picture. grin
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The Emperor Has No Clothes.

No matter where you go, there you are.

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#1932287 - 06/23/10 11:12 PM Re: Erratic oil pressure gauge [Re: UncleS2]
Jimmy9190 Offline


Registered: 02/17/07
Posts: 2971
Loc: Clermont, Florida
I have the same hash mark type gauge too. It doesn't have numbers on it, but a Dodge mechanic, who is an old-timer and knows Dakotas and the 3.9 V6 better than anyone I ever knew of said that the hash mark on the left (low end) of the gauge is about 40 psi and the hash mark on the right (high end) of the gauge is about 80 psi. Anywhere in the middle is considered safe or normal oil pressure. The psi ratings I posted are just good guesses based on looking at the gauge.

Basically what mine does is when the engine is at operating temperature and 2000 RPM, 70 MPH on the interstate the gauge stays at almost the 80 psi mark. So I am guessing 75 to 80 psi there. Soon as I stop or slow down once, it drops to between the middle of the safe zone (about 50 psi) and when I get going again at about 70 MPH and 2000 RPM on the interstate, or 60 MPH and about 1800 RPM on the state highways here, the gauge moves back towards the 80 psi mark but does not go as far as it was before I stopped or slowed down. It is at about 55, maybe 60 psi at that point.

It didn't do that before, this has been happeneing now for about 10 days. I have always followed a strict 3000 mile or less OCI and taken very good care of my truck. I like to fix things before they break and I pay very close attention to how my truck runs and sounds so I can be aware of any potential problems before they occur.
_________________________
Jimmy9190
2001 Dodge Dakota, 3.9 V6, 5-speed manual, 170K

"As long as you're in motion, you're moving in the right direction." - Ronnie Montrose


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#1932329 - 06/24/10 12:47 AM Re: Erratic oil pressure gauge [Re: Jimmy9190]
expat Offline


Registered: 05/12/09
Posts: 3750
Loc: Canada
Then for peace of mind, you might want to fit a proper, mechanical (non electric) type gauge that is calibrated.
I doubt very much the oil reaches 80psi unless it's stone cold.

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