I have a '78 250 six in my 46 Chevy pu, and it has what looks like a broken thermal vacuum switch in the block behind the distributor and ahead of the oil pressure sender port. It goes into an open oil p***age and doesn't look like a regular tvs (no bulb). Any ideas what it is (or was)?
at some point they had switches that would not feed power to the electric choke unless there was oil pressure. so you could listen to the radio at the drive-in and it would start right up when the movie was over.
Found the vacuum schematic online, this one is ca not fed. I remember a strange p*** thru vacuum or air port thru the head, but not the block and not OIL. I wonder if that was something just handy to plug up the threaded hole in the gallery. Found these pics, but doesn't show p***enger side. https://www.gmsports.com/content/1978-chevrolet-250-engine-runs-great
Rod, maybe you're right. It looks like it had vacuum ports, but what throws me is the solid base (no temp bulb or oil port). The p***age it screws into is larger than a pressure oil galley. I thought maybe a knock sensor, but the engine is too early for that; carbureted instead of EFI. I'm going to plumb up another pressure gage in the hole to see if it is a pressure galley, I wanted another pressure switch anyway to operate the electric choke
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