Express 2004 2500. 6L V8 430,000m
Oil pressure guage suddenly drops to 0 from 40. Maybe twice a week. Sometimes a minute, other times more, occasionally never before it returns to 40. Next day its good again. Had issue a few years back, where it shot uo to 80 [max] and stayed there, but that was a guage issue, that was repaired. Thinking its the sender unit?

 

it could be pressure sensor, or it could be a wiring fault (damaged harness, corroded connector, corroded ground, etc.). Gotta get your peepers on it.

 

Also possible it's the pickup o-ring causing the pump to suck air. I've heard they get hard and do that. Need to drop the pan to change it.

 

using a mechanical gauge to measure would confirm if the oil pressure is ACTUALLY dropping

 

Some of these engines have a filter in the oil pressure sending unit that clogs up and causes erratic readings. I've forgotten which years, but seems like it's the first few years of LS vans.

If your oil pressure was really zero for very long you'd hear noises from the engine that you don't want to hear from an engine.