I have stock guages in my 51. Where about should the temp guage read? It was running 2 blocks before the H. How much pressure can the stock oil pressure sender handle? The guage would be reading fine and I take the truck for a spin. The guage would keep climbing hit 80 psi and drop down to 0 psi and not move. I tried another sender and it did the same thing. I put in a 3rd but it was faulty. So do the senders can't take the pressure from my 302 or is it just the fact that the original senders I tried are all over 50 years old?

 

Nathan, it sounds as though you are using original senders with your original gages. If that is the case, it is possible to put too much pressure on the sender and render it inoperable. Here is how the original gage/sender should work. This is from my 56 manual, but I'm pretty sure yours is the same.



Oil pressure senders for newer engines don't use the bimetallic strip and contacts that the original sender and gage used. I don't think newer style senders - like the standard oil pressure sender on a 302, would work properly with your original gage.

I don't know crap about the 302, but I did a bit of reading (always helps when you don't know crap) on various web sites and there was a nice discussion of a 302 with a high volume Melling pump that was pegging a 100 psi gage, even at idle. The general consensus was that 100 psi was a hell of a lot of oil pressure for a 302 - even with the high volume pump. Most felt 80 psi would be the maximum they would like to see even at high RPM. Several folks also mentioned a rule of thumb of 10 psi for every 1000 RPM increase from idle.

First thing I would do is plug in a mechanical gage you know is good. Find out what the actual oil pressure is when the engine is cold, and warm at various RPMs. That will give you a good baseline to start from.

 

To check your stock gauges, apply 1.5 Volts dc across the terminals. The needle should move to the center. This works for the fuel, oil, and temp gauges. The temp gauge should start showing full Hot and quickly drop down to Cold before it rises back up. When mine was working, it would sit at about the 1/3 point in the summer.

Regarding oil pressure, anything more than 50 psi is a waste. Horsepower is wasted generating excessive pressure.

 

I tested the guages before I put them in the truck. I figured the temp reading was fine. As far as I know the 302 just has a stock oil pump. I figure during higher rpms the oil pressure crushed the weak old diaphram in the sender thus reading full oil pressure and at idle the oil fills up the sender thus the low or no ready. I wonder if the newer design replacement senders from restoration places will work better.