Oil Pressure

[Richard Dyer <rldyer@domain.elided>]

I have a 74 Scout II with an oil pressure problem.  I have a 345 V-8.  When I start the vehicle (cold), the engine pressure goes to around 3700.  As soon as the engine starts warming the pressure drops. It soon drops to almost zero.  It will raise some as you accelerate the engine.  I am not running the engine until I get this fixed.

My oil guage is an aftermarket mechanical guage, and I believe it to be reading correctly.

I would like suggestions on ways to fix this.  Are there any common problems with this engine that might help me out?

Thanks.