I have had a real battle over this lack of oil pressure with my new motor. Now it is down to this . I put a gauge in the spot on top the engine by the distributor. Have 60lbs there. I ran the motor for 25 minutes and had no problems. Have oil at both valve covers. I still had no pressure at the factory sending unit located about four inches about the oil filter. I changed the sending unit and that makes no difference. So I moved the sending unit down 3" to the plug right above the oil filter I had to use a short pipe nipple and an elbow to do this . There the factory gauge goes up to almost 60lbs. Why no oil pressure at the other plug? Can this be air bound or something?

 

if it was airbound you would still see 60 psi i dont think the guage cares if it is reading air pressure or oil pressure... i thought the factory sending unit was the port just above the oil filter maybe 1-2 inches... isnt the one up higher for the by-pass?

 

This got me curious, so I went out in the garage and took a look at the rebuilt88 L98 motor I've got bolted to an engine stand right now. I can only find 3 threaded holes on that part of the block. The factory oil galley hole that the sending unit goes in is about an inch or two above where the oil filter mounts, just like Spitot said. The threaded hole about 4 inches above the filter is for the clutch bellcrank pivot stud when you're using mechanical clutch linkage. The only other hole is right next to the rear freeze plug on the side of the block, and it's just a blind hole with threads in it. All 3 holes look like they have almost identical thread sizes, so it's quite possible that you had the sending unit screwed into a hole that has nothing to do with the oil galleys. If you're getting almost 60 psi in the other 2 locations, and you're getting oil all the way to the top end of the motor, I'd say everything is just fine with the engine. Just leave the sending unit hooked up to whichever of the two working locations you prefer better.