[Silva455]

Hi Guys,

Was wondering if anyone here has ever ran into this problem and how was it addressed. I have a freshly rebuilt 455 in my 70 Firebird and it has less than 500 miles on it. I added the factory oil and temp rally gauges with a new wiring harness in the engine compartment and dash.

After the first few times of starting it, the oil gauge worked and bounced around in the area of the normal PSI range. Temp gauge works perfectly. One day I go to start the car and notice the needle wouldn't move, was stuck down in the red portion stating that there was hardly no PSI. I checked the new oil pressure sensor and all wires and seemed good. Go to fire it up again, and the gauge is back to working. Then few weeks later, same thing not working again. Sent my gauges off and had them tested. They passed, and it was recommended I add dampening fuild since it was low, to help the needle move softer. I passed based on the quote. While out, I cleaned all the terminals on the cluster and reinstalled everything. Even another new oil pressure sending unit, but different brand this time around. It worked fine for a few trips. I parked it and maybe a month went by and same thing again, low to hardly no pressure reading on the gauge. I have started a few times now, weeks apart and not movement on the gauge. I did unplug the sensor and the gauge moved to half way, stopped, and then went to max pressure. I haven't started it since this.

Car has a 455 that I rebuilt.
New oil pump Melling M-54D-S
New oil shaft
Using a 90 degree oil filter housing off a Bonneville
I already changed the break in oil and have a new Wix filter installed.

Next I was thinking of installing an oil pressure gauge and checking that. Any other ideas what's causing this? I was thinking electrical all this time, but now I'm, concerned that maybe its something else.

[srmmmm]

I would verify with a good mechanical gauge. Sending units can be inconsistent.

[Formulabruce]

Try quickly grounding the wire to the oil pressure switch.
The oil pressure switch is a gradual ground. The higher the pressure, the more it grounds. Should get full deflection when wire grounded out IIRC.
Seems to me you have a partial ground on that wire somewhere. Could be inside fuse box where wires connect to fuse holders.
Note, your engine needs the original ground wire at pass side rear head hooked up to firewall. Not having this can cause items to seek " other grounding paths".

[fbody_mike]

If it was zero PSI while running you should hear the lifters clacking away, unless you have solid lifters.
Check the engine grounds. Maybe the next time it does it, try grounding the body of the sender and see if it changes.

[Peter Serio]

First thing is to check (refer to post #2 above). If you have steady oil pressure there, next is the dash gauge.

GM "factory option" water temp and oil pressure gauges, after 50+ years have a 95 to 98% failure rate.

Another issue is new aftermarket parts (the senders you tried) are no longer made in the USA and those haven't been made here in over 25 years.

They are made today 1/2 around the world and those people do not have a car (like the car you have) over there to test the sender on. They also have no shop manual to your car. They have never even seen the car you have. The GM blueprints to make these kinds of parts are only available after you buy into a special program GM has now to get them. And GM now asks for up front money before they will send you a copy of the blueprints. I doubt that any new gauge senders (for a car made in the USA over 50 years ago) are made 100% to specks or from the original GM drawings.

[Silva455]

Thanks for the help guys.

Update: Yesterday after work I decided to go mess with it for a few. I plugged the battery in. I unplugged the sensor and plugged it back in. I could hear the needle from the gauge moving as I was doing this. I started the car, and the gauge read oil pressure where is was suppose to be. Great! For insurance, I took off the oil fill cap on the valve cover, and I could see a steady stream of oil flowing at the lower edge of the valve cover. I let the car warm up and turned it off after about 10 min. I came back about 15 min later, and started her back up. Gauge decided to not move and stay in the red zone of the left. While the car was running, I unplugged the sensor and plugged it back in and the gauge started working fine and showing pressure.

Now what do you guys think? I cant remember if I unplugged my battery between the two starts. But I always unplug my battery between start ups since it sometimes sits for weeks. No idea if that has anything to do with it, probably over thinking. Could be a crappy sensor like mentioned below. Or a bad ground like mentioned below. But the temp gauge works fine and that shares the same gauge housing and engine ground. Oh and when I installed my engine to firewall ground behind the head, I made sure to sand off any paint on both surfaces.

[Peter Serio]

My best thought here is that the internal buffering fluid in your oil pressure gauge is missing. After all these years it leaks out. That is why your can hear the pointer. On a perfectly good working gauge (oil and/or temp) you should never be able to hear the pointer as it sweeps the dial.

The buffering fluid in those 2 gauges provides about a 1 second delay in reaction time. This is designed into those gauges to keep them working but only for the original lifespan of the car. (First year to year 11,12 or 14). The buffering fluid serves the same purpose as the oil does in a shock absorber. It slows down the piston and it also lubricates the moving parts.


Another thought is there are resistors on the back of those 2 gauges. When they get old sometimes those go bad. Another thing I see all the time is the ends of those resistors are silver (it is actually 90% silver and 10% copper). The silver is a foot print as far as the threaded steel "posts" that bring current into and out of the magnetic coils. After 50 years that silver turns black, also the steel posts rust and corrode. Anything like that going on behind the gauge(s) can cause it to work and then stop working, and all of a sudden start working again. The cure would be to clean & inspect all of those electrical touch points and test and/or replace the resistors.