I have a 6.5 liter turbo diesel 99 3500 work truck - today the pressure suddenly dropped to 0 at idle - and seems less than normal at 2K rpm. The motor has 106K on the clock. I last changed the oil 3K ago when I bought it. Tonight I changed the oil and filter because it seemed thin and watery. Tomorrow I'll see if there is any change. But, if after it warms up, it remains the same, what could cause the problem?

The other odd thing - the guage seemed a bit erratic jumping up and down when it first happened but steadied out but lower, though it seems to jump up quicker than before when I step on the gas. Could that indicate a bad pressure relief valve? (do these trucks have them?)

Should I not drive it in this condition?

Best, G

Don't drive it until you have put a direct reading gage to check that oil pressure.
My friend how has a 3500 wrecker had the exact same indication last week. Against my advice he drove it believing the sender was bad. Engine siezed the next day.