The parts book shows a 2 way tee. One to the head and one to the oil gauge. The 3 way is the same but you have one more leg for the oil filter. Both the GMC 228 and 302 engines in my garage connect the oil pressure gauge to the main oil gallery on the lower left side of the block about 5 inches from the rear. The place on the front of the block that the Tee threads into has a small hole at the bottom, restricting oil flow and therefore reducing pressure into the Tee. My 2 way Tee feeds the oil filter and the head. I'm guessing that the 3 way Tee is for some accessory on larger trucks. The drawing you posted shows a 3 way Tee with the 3rd line ending in an upturn right behind the generator. I'll bet Kenneth (GiantMountainClimber) knows what it connects to.
Last edited by Bill Hanlon; 06/24/2026 2:20 PM.
'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.
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