Sudden wild jumping of oil pressure gauge needle

[Carl Stouffer]

The safe thing to do would be to follow your mechanic's advice and get a test gauge on it.

Then again, it could be a bad electrical connection, if it is the factory or an aftermarket electric gauge. Hard to say. If it was still above the
add line, it doesn't sound like it was low on oil.
--
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles,
Solar battery charging. GMCSJ and GMCMI member

 

[jim kanomata1]

Personally had an experience with a 403 that had All the rubber in the fuel
system changed out by our shop.
One day the oil gage got erratic reading, so I pulled over to see if was a
bad connection.
I then went to check the oil level.
The oil was dripping out of the dip tube and I put my nose to it and
smelled gas.
My guys did not realize that the pump has rubber diaphragm, so they did not
change it.
Well, the engine was starting to knock, so I just drove it back to the shop
and informed our guys that when I say to changeALL rubber in the
fuel system, it includes the diaphragm, it was the original.
Had to rebuild that engine.

> The safe thing to do would be to follow your mechanic's advice and get a
> test gauge on it.
>
> Then again, it could be a bad electrical connection, if it is the factory
> or an aftermarket electric gauge. Hard to say. If it was still above the
> add line, it doesn't sound like it was low on oil.
> --
> Carl Stouffer
> '75 ex Palm Beach
> Tucson, AZ.
> Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive,
> Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American
> Eagles,
> Solar battery charging. GMCSJ and GMCMI member
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>

--
Jim Kanomata ASE
Applied/GMC, Newark,CA
jimk
http://www.gmcrvparts.com
1-800-752-7502

 

[Ken B]

What you have sure sounds electrical to me. I would remove the electrical connector from the sensor located on the top front of the engine. Clean
the contacts with a pencil eraser and reinstall. If that does not fix it, stop by an auto parts store and get a new sender for a Oldsdmobile Toronado
b]WITH GAUGES[/b], not one for a car with an oil pressure light. Screw it in in place of the one you have and see what happens.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

 

[Matt Colie]

> Hi. Pretty sure I found the switch connector. I could not find the diagram in the manuals so used process of elimination. Cleaned them up. Fingers
> crossed. G.

Grant,

It is up in the front of the engine.
Let us know if that got things settled.

Matt
--
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit

 

[Carl Stouffer]

> Hi Matt and everyone else.
>
> I’m still not sure if I found the oil pressure sender / switch but I did clean up the contacts on what I guessed was the switch. Also on the
> water temp sensor.
>
> We were in Massey, ON which is a small, northern Ontario town. Left the camp ground and drove to the local shop. Closed for the holiday weekend.
> We met a nice fellow, Billy, across from the shop. He called his father who is a licensed mechanic. Billy is familiar with building 350 small
> blocks.
>
> At this point he suggested starting it up to listen if it was oil starved, etc. I stepped over the opening, twisted the key, the engine jumped to
> life and the OIL PRESSURE GAUGE PINNED STEADY at 5/8 on the gauge. Based on that, plus the normal sounding engine Billy and I figured it was good to
> go.
>
> From Massey to Toronto it is “mostly” downhill. The coach ran better than it had the last 10 days of the trip. Strong and smooth. The gauge
> only dropped a bit and slightly giggled when coming to a stop. Although I was expecting massive failure any second this was the best, and longest,
> day of driving we’ve had with the coach.
>
> So once again thanks to strangers.
>
> What was the cause? Not sure. Coincidental degradation of the contacts? I suspect the continuous 6-8% grades in 3rd and 2nd gear may have
> something to do with it - does the oil pick-up get affected by such inclines?

The coach would have to be upside down or laying on it's side for the oil pick-up to be starving.
--
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles,
Solar battery charging. GMCSJ and GMCMI member

 

[Ken B]

Grant,

Late this afternoon an immaculate T6 Texan ( https://en.wikipedia.org/wiki/North_American_T-6_Texan ) showed up at our airport with a complete
electrical failure after refueling. Absolutely nothing electrical worked. Then it started working again so he took off. 30 minutes later he came
back and none of the airport mechanics were still around. So I agreed to take a look at it. I found something similar to yours. It was an
intermittent connection on a switch that energized a relay that puts the battery online with the rest of the airplane.

I cleaned up both of the terminals on the switch and tightened them securely. The problem went away. I hate working in intermittent problems. You
never know for sure that you fixed it.

He called me this evening from some place in Virginia and said he had no more problems in 4+ hours of flying. I told him if he did have any more
problems to replace the almost 75 year old switch.

It was a similar problem too what I think yours is, with an oxidized / loose connection. It just affected his $250,000 airplane in a different
circuit.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

 

[dave king]

Re Mechanical oil pressure gauges. Here's my opinion based on experience/ observations of other peoples stuff
A good mechanical gauge will show you things the small sweep electrical gauges will not
There are some electrical gauges with lots of "sweep" I know nothing about those.
I do NOT and will NOT use the "plastic" hose that comes with a lot of name brand mechanical gauges.
I've currently got a well supported copper line but I may replace it with a steel braid covered Teflon hose.
(working hardening concerns from engine vibration)
Put the gauge where it is easy to see and use the lighting kit so you can see the reading at night.
I would suggest putting the gauge in a position so if it leaks the oil doesn't go on your leg(s) especially
if you drive in shorts or a dress (for the ladies)

On the subject of gauge placement NEVER put a direct reading mechanical fuel pressure gauge in the cockpit.
--
DAVE KING
lurker, wannabe
Toronto, Ontario, Canada

 

[Greg C.]

Just FYI. I was driving my 77 in the local Christmas parade last year. During the parade, my temperature started to rise, and the oil pressure started
fluctuating. I was about to panic and pull over. The gauges weren't steady in their reading, which triggered another thought. I had the lights on, so
I switched them off just to see what would happen. Voila! Temp gauge snapped back to normal, oil pressure gauge steadied up on its normal reading.
Lights back on, same symptoms immediately resumed. Bad dash ground. There is a wire attached to the metal frame of the instrument panel, which ducks
into the wiring harness and then pops back out to be attached to a sheet metal screw screwed into the aluminum fire wall. Possibly, but not certainly,
to quote Captain Ron, "There's your problem!" Worth a look.
--
Greg Crawford
KM4ZCR
Knoxville, TN

"Ruby Sue"
1977 Royale
Rear Bath
403 Engine
American Eagle Wheels
Early Version Alex Sirum Quad bags

 

[bob heller]

The oil gauge on my GMC started doing this about 10 years ago. I replaced the sender, same thing. Someone back then told me that where the gauge
attaches to the circuit board there is a resistor across the terminals and over time the connection between the gauge, the resistor, and the circuit
board gets intermittent.

I've never taken the gauge cluster out to fix it, I just keep on driving. Pure laziness on my part. The original 455 still runs fine, no abnormal
noises, so the actual oil pressure must still be good.
--
Bob Heller
1974 X-Canyonlands 26ft
Original 455 except for timing chain, Rockwell intake, valve covers.
Ferrara air bags. 150k miles.
Winter Springs FL

 

[john r. lebetski]

Bobby you can test this without taking dash apart. Simply ground and open the connector that goes to the sender. Gauge should read only either
extreme. If bouncing then it’s probably what you suggested (unlikely as they are not usually problematic) I suspect failing damping mechanism in
sender.
--
John Lebetski
Woodstock, IL
77 Eleganza II