Sudden loss of oil pressure.
 

Have a 75 400 .030 over, 62 cast heads. Engine has been together for probably 15 years, has maybe 7000 miles. Had car out at Woodward a month ago, did a local cruise at the end of August. Everything was fine.

Went to move the car a few weeks back, no oil pressure at startup. Next day I pulled coil wire and oil filter. Cranked over engine. had oil pouring out of the filter housing when cranking. Installed new oil filter, filled before putting on. Pulled oil line off gauge in car (mechanical Sun) and cranked engine over. Got oil out of the line within 10 seconds of cranking. hooked gauge back up. Started car, had 60-70lbs cold like normal. Shut the car off, cleaned up. and fired it up again. Took it for a 15 minute drive. 15-20 lbs at idle like normal. Went to move it last night, same sceenario. No oil pressure. Thinking a stuck check valve. Is there one in the oil filter housing? I can't remember, it's been a while since I've messed with the oiling system.

Faulty gauge would be my first suspect. Did you hear valve clatter when the pressure was zero?

There's a spring/ball in the pump to moderate oil pressure and a bypass in the filter housing.

The valve in the filter housing is set to bypass oil around the filter and into the motor when ever there is a 20 psi difference between the 2 should a filter ever become bloccked off.

Yes this means that the oil gets filtered less then you think it does!

As posted if your not hearing the lifters clack then you likely still have oil pressure .

Idiot light on the dash still hooked up? Always good to tap pressure somewhere else and use both of them. If they both say no pressure then you almost certainly have a problem. If only one says no pressure then it's probably a gauge/sender.