'74 Oil Press Gauge suddenly reads low

[pressonregardless]

Looking for a couple of volt/ohm measurements as my 1974 CS1 1756cc Oil Pressure gauge always read low ( many years it never indicated past mid-scale) but now barely it creeps above zero when cold. With a warm engine the oil pressure gauge rests just above zero at 3-4000 rpm. Warning light is off, fresh oil & filter change after this problem appeared using Shell Rotella 15w-40 just to be safe. Rather than "swap parts" I took some readings I need to confirm. I know the engine is fine, as we've driven it 100's of miles in this condition.

1) at Oil Pressure sender, wire disconnected, and engine at idle I read 8.5 VDC to ground on the wire.
2) at Oil Pressure sender, wire disconnected, and engine at idle I read 400 ohms to ground on the sender connector.

If anyone has a vehicle in this age range ( '74 - '78 ) and would be willing to crack a meter out, I would appreciate it!

[kilrwail]

I'd be happy to help, but I'd have to remove the undertray! Not happening today

[pressonregardless]

You should be able to open the hood. On the Drivers side of the engine, above the oil filter are both the Oil Pressure switch and Gauge sending unit. Appreciate the help!

[kilrwail]

Sorry I didn't look at this earlier. All of that stuff is under the alternator on my engine and hard to reach, let alone see.

[Odoyle]

Listen to the noise from the oil pan while the car is idling, if you hear excessive noise it may be the oil pump going.

[spider2081]

I have a Veglia gauge and sender out of the car. The sender measures 300 ohms with no pressure applied. I would think as the oil pressure goes up the resistance would go down from the 300 ohm area. So I think 400 ohms would make your gauge reading zero or even a little less that zero.

[pressonregardless]

Thank you all for sounding in.
It may be my sending unit is failing, I guess I could email Ramzi at AutoRicambi and ask what a new sender resistance measures before I order one?