The threaded hole to the left of the cast R is at cylinder 5. That hole is there and threaded for every GMC 228, 248, 270 and 302 I've ever seen. The temp gauge screws in there.
The raised area to the right of the R is at cylinder 6 and is there on every 228, 248, 270 and 302 engine I've ever seen, but is only drilled and tapped on military engines. This is where the bypass tube originates.
I didn't check, but I'm pretty sure the hole size and threads are the same for both holes.
Last edited by Bill Hanlon; 11/12/20253:15 AM.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
