Same thing. Most likely a bad sender or plugged hole.

Ken Styer

I haven't yet experianced any problems with my sending unit, oil pressure nor anyother gauges. Did you check your circuit board behide the cluster?

IRON 82

I don't know if later C-3s had mechanical or electrical gauges, but I had a '69 oil pressure gauge that didn't work either. The problem ended up being sludge had actually built up in the gauge itself. I was actually succesful in cleaning it, but it took a very long time to "flush" the crap out of it. Obviously the gauge had to be removed to do this. Another gauge would have been a more prudent choice, but I can be a bit stubborn when parts don't work properly. One way to Isolate the gauge would be to buy a cheap gauge and just run your sender wire or tube to it. Those itty bitty tubes can stop up with sludge too. It's trial and error.

I've re-read some of these posts, if you guys are getting 40 lbs at lower rpm's or idle, you're in good shape. If I recall, the rule of thumb is 10 lbs for every 1000 revs. 50 lbs at 5000, etc.
The jumping can be explained by a pressure relief in the system. Some builders "beef up" the spring. It will make the gauge jump!
If your rockers aren't rattling, you probably don't have much of a problem!

Dave your on target, but the key word in your reply is "IF". When the gauge isn't working, you don't know. Good guesses are usually okay. Usually.

Ken Styer