Jim Carter shows a 1936-1939 gauge decal kit for "Pick up trucks". The oil gauge reads 0 40 80. I see Chevy is 0 15 30. There may be some GMC at 0 15 30 or you have a Chevy gauge stuck in there by a PO. They say it's for a 80mph Speedo. 1936 was the first year for GMC "pick ups". before that they only built "big trucks". They did not have a right sized motor yet for a pick up, so they used an Oldsmobile 213 full pressure car motor. The vortec is 262. This is so old it's hard to get info. Anyway I was thinking:
1. The 1936 gauge is designed to show a certain range of pressure.
2. The rule of thumb is 10psi per 1000RPM. I.E. 5 psi at 500 RPM idle. 20 PSI at 2000 RPM. The pressure will fluctuate/not match rule of thumb all the time for various reasons. Oil Wt,, temp, gauge calibration, worn motor.
3. If any gauge shows 5 psi and up, you are OK.
4. I don't know about that fuel pump shut off using oil pressure or if it is working properly or causing issues. Of course you do not want to use that during testing. Just one mechanical gauge, no Tee. Then the 1936 gauge, no tee. Then any other mechanical gauge, no Tee. After you see a consensus, you can decide on what to do/use. The 1936 gauge will not be super accurate. The internet says the vortec gauges were not accurate.
The 'new" mechanical gauge may be the one to trust during testing.
Bottom line is a 0 15 30 may not be calibrated to give you a comfortable reading. As you say It should be maxing out at about 3000 RPM. 5 psi at idle and so on.
YES........Maybe keep the 36 gauge for looks and hook up the "safety" electrical gauge somewhere.
Last edited by bartamos; 02/22/2025 7:06 PM. Reason: clarification
