My oil pressure may be too low

[Unregistered]

My oil pressure may be too low. I believe the gauge is the original with the boat which was built in 72. There are two scales. The scale underneath the black line shows single digit numbers. The scale above shows number in the 10's. The needle settles at about 25, maybe closer to 30 at all running speeds. I know I have a very thin oil mixture because have a quart of Marvel Mystery Oil as one of the 4 quarts. I don't know if that could cause the lower pressure reading. If not what are you thoughts?

[Don Moyer]

I'm not sure how to resolve the uncertainty in your gauge readings (other than to install a direct reading gauge for comparison), but depending on the RPM at which you're cruising, an oil pressure of approximately 30 psi would be quite normal. The rule of thumb that we have used for many years is to set the regulating valve to maintain between 35 and 40 psi at your favorite cruising RPM with the engine fully warmed up.

Don