On the Chevy 6 inline 6 and the 4 cyl the distributor and housing do nothing but turn the oil pump drive. They are not like a V8 and use the distributor housing to block a oil path.
I bet if the engine was turning over the pressure would get where you want.
I bet the oil bypass was opening in the oil pump, it will limit the pressure to what ever the spring is set to. The higher viscousity oil will also bypass easier than thin oil. Bet everything is OK.
Last edited by tlowe #1716; 01/23/17 11:31 AM.
