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Q: Gauge and light show no oil pressure on 2001 Ford F-250 Super Duty

Truck ran fine, parked it and came back to it 2 weeks later to run errand. At start up heard unusual whirring sound and clank/thump (my son heard thump/clank, I didn't). Engine started and was running fine, slight lifter rattle (for about 2 seconds, she does have 148,000 on her) intially, which quit immediately. Noise made me look at gauges, all was fine except no oil pressure showing on gauge and dummy light for oil pressue was also on(it has both). Immediately shut off engine after running only 10, 15 seconds at most. Checked oil level, which was fine. No leaks underneath. First thought-sending unit gone out but dummy light also lit up (are both operated off same sending unit?). Started it up again to see if pressure would come up but nothing after 3-5 seconds so I shut it down again. Too scared to start up again so I had it towed to local shop to have pressure test performed tomorrow.
There was oil splash on dip stick when I pulled it, which would make me think oil was circulating. I would think that the windage tray would keep the crank from slinging oil everywhere on start-up, which led to my thinking that the sending unit might be inop and that oil was circulating, maybe I'm wrong about the crank slinging oil. Either way, I wasn't sure enough to take the $4K chance of blowing the motor (for a used, installed engine)
just to find out.
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I am no expert on Ford but have information in front of me. The oil pressure switch is near the oil filter just above the oil cooler with the two water hoses attached to it. The wire at the oil sender unit is white/red. My information says the sender unit turns on the warning light when the switch is open and this also causes the gauge to read LOW. With normal oil pressure the light goes out and the gauge reads Normal. Pretty stupid in my view I would want to see a low oil pressure light on at below 7 psi and an oil pressure reading that meant something. Put a drain pan under the engine disable the engine so it will not start, unscrew the oil filter and crank it over, if you have oil pressure the oil will pump out if you have no oil filter no oil will pump out, that's the quickest and easiest test. If oil does pump out screwing in a mechanical gauge to verify correct oil pressure would be next. The oil pump replacement instructions say take of the crankshaft pulley, the front cover and oil pan. The labor time given is almost 15 hours depending on transmission and equipment.
Great information! Thanks! The filter removal check seems like common sense but, even tho' somewhat of a gearhead, I would never have thought of it (no comments, please..). I'll be sure to take this information with me tomorrow to the local shop that is doing the diagnostic for me and make sure they do the filter removal check before firing it up and doing a mechanical check.

Thanks again,
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