Oil pressure gauge 1948 car

[34pickup]

1948 V8Coupe. When I turn the ignition switch on, my oil pressure gauge moves up to show full oil pressure but when I use the starter button and the engine starts running, the gauge goes back down to zero. Is it possible that the previous owner crossed the wires on the gauge to operate backwards or do these gauges not operate in that manner?

[meric42]

Sounds to me like you might have the wrong sender unit or the one you have is faulty.

It seems to be operating like a switch for an oil pressure light i.e. with no oil pressure it is connecting the gauge to ground thus turning the light on (making the gauge go to full) and with oil pressure breaking the ground connection, thus the light goes out (making the gauge go to zero). A photo of the sender unit might help?

[34pickup]

That does sound like what its doing. The wiring on this car is atrocious. I think I will connect a mechanical gauge up to it so I will know what it is doing.

[JSeery]

I would start by connecting a good mechanical gauge to assure you indeed have oil pressure! The current flows through the original gauge to the sender which is a ground. There are points in the sender which open and close as the current heats it. The rate at which the points open and close determines the gauge reading. It is possible that the points need cleaned. Not a simple task, but it is doable. There have been past threads on taking the different senders apart and attempting repairs.

[34pickup]

Originally Posted by meric42

Sounds to me like you might have the wrong sender unit or the one you have is faulty.

It seems to be operating like a switch for an oil pressure light i.e. with no oil pressure it is connecting the gauge to ground thus turning the light on (making the gauge go to full) and with oil pressure breaking the ground connection, thus the light goes out (making the gauge go to zero). A photo of the sender unit might help?

Here is a photo of the sending unit I took out of the engine. It doesn't look like the ones in the car parts catalogues.

[1942deluxe]

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Aftermarket sender for sure. Should have an 80lb sender.

[1942deluxe]

Dennis Carpenter has them . Ford part number 41A 9278.

[34pickup]

Thanks.