Have a 1948 F-3 flathead w/39,600 miles. Miles are not documented but seem to be original given the condition of the truck. The oil pressure w/30 weight starts at 45 but as the truck is driven after 30 min drops to a steady 15-30. There is no oil blow by on the plugs or at the top or bottom oil/crank case vents. The compression check on the left side back to front is 70, 85, 80, 80; on the right side back to front is 85,86,80,85. When first started the truck does have some gray smoke from the exhaust but as driven and engine temp comes up that smoke goes away. Don't know the engine specs on oil pressure, compression or best oil to use, would appreciate any input. Thanks

 

On what gauge? If the dash gauge, irrelevant. They are wildly inaccurate, in many cases. Use a known good mechanical gauge. (It won't be easy to hook up, unfgortunately, the sender is in a bad place) Are those numbers at idle or cruising speed?

Was this with the plugs all removed and throttle wide open? Not great if so, not real bad either. Has the truck been run regularly recently? Some run time may improve the numbers.

 

Flatheads are notorious for low oil pressure at hot idle. 15 p.s.i is fine. I recommend 15W-40 diesel oil, it helps the oil pressure on my 37 so that the gauge show something at hot idle.

 

In a Lincoln V12 of that era, those would be exceptionally good pressures!

 

Minimum oil pressure would be 10 PSI per 1000 RPM. Remember oil pressure only serves to distribute the oil around the engine. It is the film of oil that separates the metal parts.