the crankcase oil pressure is 7-15psi so oil is more likely to flow into the cooling sytem. Oil pressure on his GMC engine will be a lot higher than that. My 228 is 45-50 PSI when warm at highway speeds using 15w40. Maintenance Manual calls for a rebuild when that drops below 25 psi.
'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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