I have a 6 cylinder '99 Ford E150 and though it has plenty of oil, the oil pressure gauge drops and the idiot light comes on whenever it stops and comes to idle. Pressure seems fine when driving but dips at a stop lights etc…
for what its worth, my 75 ford f100 has been doing this for many years with no ill effects. my 1990 jeep Cherokee has just started this. I m going to change the oil pressure sending unit in the jeep and see if that fixes the problem. that’s the easiest and least harmful of the possibilities in my opinion.
does it do this when its cold or just when it gets warmed up thoroughly?
it only happens when warmed up in both of my vehicles
dropping the oil pan and cleaning the screen on the oil pick up tube couldn t hurt and may be easy on your van as it is on my pickup. dropping the pan on the jeep is a big job
If it is not the oil sender, as @wesw suggested, your bearings and oil pump may be worn to the point where the pressure cannot be maintained. Solutions could be, drop the pan and replace the oil pump with a high volume, not high pressure, pump. You might be able to replace the bearings with 0.001 oversize units while the engine is in the truck as long as the crank is not scored up.
You might also consider a slightly heavier weight oil. 10w40 instead of 5w30, for example. This will get you down the road for a while but save your money for a newer vehicle as this one can see the light getting closer…
When the oil pressure drops to zero, is there any valve noise from the engine?
If not, try replacing the oil pressure sending unit.
No. I don’t hear any valve rattle but then again, I rev up the engine at stops now to keep it out of the red.
I had the same problem years ago with my 1971 Ford Maverick with the 250 cubic inch 6 cylinder engine. We were on a vacation and the oil pressure warning light would come on when we stopped for a traffic signal. It would go out as soon as I accelerated from the stop. When I got a chance, I pulled into a parking lot. When I checked the oil, it was right up on full. I then started the engine and let it idle. There was no valve noise from the hydraulic lifters. I then removed the oil fill cap off the valve cover. I could see the oil being pumped up to the top of the engine. I ignored the oil pressure warning light for the rest of the trip. When I got home, I had the oil pressure sending switch changed and that solved the problem.