2020-B1-7

Author Topic: Bouncing oil psi needle  (Read 151 times)

EspriTA350

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Bouncing oil psi needle
« on: February 22, 2021, 09:46:19 AM »
Before I took my car off the road to do a performance rebuild on the motor, I was having an issue with the oil psi needle bouncing/fluttering very rapidly. Ever since last year, it would always be between 50-70ish (I have an aftermarket oil pump, that's why it goes higher than stock) and fluttering/bouncing very rapidly several times a second. Engine speed didn't have any notable effect, the needle would flutter whether it was at idle or at cruising rpm. I tried a couple different oil filters after asking a couple friends about the issue (they suggested maybe something was wrong with the oil bypass), with no change to the gauge. I never did get around to checking for a bad ground before I had to take the car off the road. However, I recently discovered that the block had a crack in it. I've started wondering, could that crack have been the cause of the gauge "flutter" or should I be looking for an electrical issue somewhere?
« Last Edit: February 22, 2021, 10:00:08 AM by EspriTA350 »

firebirdparts

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Re: Bouncing oil psi needle
« Reply #1 on: February 22, 2021, 10:37:53 AM »
My gut would be electrical;  It would be interesting to see if the gauge flutters while connected to a constant resistance in the place of the sender.  I.P. Ground would certainly mess it up, but it ought to mess up all the gauges.
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Joe Bays
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1978 Skybird 350
1978 Redbird 305
1979 Redbird 301 4-speed
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EspriTA350

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Re: Bouncing oil psi needle
« Reply #2 on: February 22, 2021, 11:29:41 AM »
My gut would be electrical;  It would be interesting to see if the gauge flutters while connected to a constant resistance in the place of the sender.  I.P. Ground would certainly mess it up, but it ought to mess up all the gauges.

My thinking was perhaps the crack was causing momentary interruptions in oil flow, several times a second, causing the needle to flutter. Is that a crazy idea? I don't have that problem with any other gauge, but the speedometer does do this:
If I floor it from a stop, the speedometer needle would stay at 0 mph no matter how fast I'm actually going, until I let off the gas. Then the speedometer needle will jump straight to the speed I'm actually moving at. During normal driving or brisk acceleration when I'm already in motion, the needle doesn't "lag" the slightest. I've been told this is a worn speedo gear, but thought it worth mentioning since you suspect a ground.

81Blackbird

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Re: Bouncing oil psi needle
« Reply #3 on: February 22, 2021, 11:37:28 AM »
My oil gauge did the same thing but not as bad as yours.  I change out the oil pressure sending unit and it was fine.  Perhaps it has a bad spring or diaphragm.

firebirdparts

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Re: Bouncing oil psi needle
« Reply #4 on: February 22, 2021, 01:45:05 PM »
I guess it's a wonder that oil pressure is as stable as it is.  There's a lot of stuff going on in there that could make it vary.  The gauges aren't really stabilized.  I'm not sure how they even do that, but I had a 1953 Chevrolet pickup when I was in highschool, and the fuel gage in that thing had some sort of viscous dampening  It would only move really slowly.

Anyway, I think real pressure shockwaves are possible but I don't know how likely that is.  When in doubt, I always put on a mechanical gauge and think it over.
I want to be like Paul Kenny when I grow up
Joe Bays
1977 Y82 4-speed (red interior)
1978 Skybird 350
1978 Redbird 305
1979 Redbird 301 4-speed
1992 Lincoln Mark VII LSC/SE (red)
1970 Datsun Pickup
1953 Chevy pickup (converted 4x4)
1988 T-bird Turbo Coupe

EspriTA350

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Re: Bouncing oil psi needle
« Reply #5 on: February 22, 2021, 03:53:40 PM »
My oil gauge did the same thing but not as bad as yours.  I change out the oil pressure sending unit and it was fine.  Perhaps it has a bad spring or diaphragm.

What brand did you use?

MNBob

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Re: Bouncing oil psi needle
« Reply #6 on: February 23, 2021, 03:49:14 PM »
Mine is doing the same thing.  I replaced the sender with a new one and it made no difference.  I have grounds everywhere.  All the other gauges are fine.  I'm going to digital gauges this summer.
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EspriTA350

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Re: Bouncing oil psi needle
« Reply #7 on: February 23, 2021, 08:42:06 PM »
Mine is doing the same thing.  I replaced the sender with a new one and it made no difference.  I have grounds everywhere.  All the other gauges are fine.  I'm going to digital gauges this summer.

That's not encouraging.

Wallington

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Re: Bouncing oil psi needle
« Reply #8 on: February 23, 2021, 11:14:29 PM »
Digital still uses an oil pressure sender, which, if faulty, will still be faulty in reading. Not uncommon to replace bad parts with bad parts again.

Re: Bouncing oil psi needle
« Reply #8 on: February 23, 2021, 11:14:29 PM »
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