No Oil Pressure?!

Maybe its just the sending unit that is shot. It probably would not hurt to change the oil and filter.

Good starting place, to be sure the indicator is working.

I dont know those engines, but in general, sludge, loose oil pickup, bad pump, snapped oil pump drive shafts have plagued a variety of other engine designs.

The first thing I would look for is a bad pressure switch. I would also substitute a mechanical guage to find out exactly if and how much pressure it has. If you only have a light, it may be that the pressure awas low when it was last running. IIRC, those pressure switches are set to come on around 5-7 psig which ain't much but is adequate for hot idling. If it never went anything above the pressure needed to turn off the light, you will never know with a warnig light only system. 100K is a lot on a gasoline MH engine simply because it is under a fairly constant high load.

Lugnut

That was my first thought/hope, but the valve train was rattling quite a bit more than what is usual for this engine. I don't want to run it any more until I find out for sure.

The valve train was rather noisy as well; enough to make me shut it down immediately and not want to re-start until I have more information. And this thing does have an electric pressure gauge as part of the instrument cluster.

This engine had not been run at all for at least 9 months, maybe a few more. There were no problems with oil pressure when I parked it last summer.

You can get an adapter shaft to run the oil pump with a good drill from most auto parts stores. Many will have to order it for you. It is designed for priming an oil system on freshly built engines. Remove the distributor and make sure the drill is turning it the same direction as the distributor turns. If you have a guage connected, you should see pressure build. Also, at 100K miles, it may be a matter of a plugged oil pickup screen. It may have sat long enough for sludge to settle from the oil to the bottom of the pan just to get sucked up like the dry film that forms on the surface of paint in long term storage. If that is the case, you may get away with a pan gasket to clean the pan. Be sure to change the new oil after a couple hundred miles just in case it starts again. Having been 3 qts low, I would suspect the oil was quite hot when it last ran which can break down the oil and cause it to be more like grease than oil when it cools.

Lugnut

Thanks for that.

I'll look into a way to spin the pump and hope that I was just sucking air. That would be the easiest solution for me. I have pretty easy access to the top of the engine with the doghouse removed in this vehicle.

Otherwise, I'll have to hope that I can get the pan off with the motorhome on the ground and the block still in place. I'm not looking forward to rolling around in the weeds where she's currently parked behind the barn, but what can I do? Maybe I can find a way to push this beast into the barn without damaging anything, but I'll need to get creative. Once in the barn, though, there isn't more than a few inches of clearance to lift this thing if need be. I should have built a taller barn or poured a pad outside somewhere. Live and learn.

It's a Chevy by Jo, not an F40.

10 seconds isn't enough for a diagnosis. If you must, overfill it 1 or 2 quarts and give it some revs, it will pick up. Only drawback is a little extra wear on the pump, maybe a thousand miles or so. But, what are you going to do? Crawl around in the weeds and pull the pan for nothing? You can use the starter or use the drill, same difference. Just disconnect the coil.

wws

My ten cents worth. Drain out what is in it and pay attention to the consistency of what comes out. If it did get overheated and congeal it will be obvious. If not it probably needs changing anyways after siting for 9+ months. Before you start it unplug the primary wire you from the coil and crank it for a couple of minutes. If it doesn't prime the system and show pressure dig a little deeper. ch

The pump rotors are probably just dry because the oil all drained back to the pan. The pump's interlocking rotors rely on a fairly thick film of oil to seal them. When dry (which really means the oil film is too thin, not absent completely) they tend to leak air and take a good while to prime up.

You can get an adaptor shaft to run the oil pump with a reversible drill (I don't know which way the pump and distributor rotate in a big-block Chevy, but many engines require you to spin the pump CCW.)

OR you can submerge the pump for a few hours by putting about 3-4 extra quarts of oil in the engine, which should be enough to "wet" the rotors. Crank it up briefly to confirm oil pressure, then change all that extra oil out immediately. This would be what I'd do, personally. Getting at the distributor way in the back and then re-setting timing on a Chevy can be a PITA that you just don't need.

OR you can just light that sucker up and run it for 30 to 45 seconds. The valve train may rattle with the lifters pumped down, but so long as you don't race the engine it shouldn't do any harm for that brief period. 10 seconds at a time just isn't long enough to pump up after such a long time sitting.