Ok
New 160 F thermostat
I’d say within 5-10 minutes from cold had steam or at least bubbling coolant out of open rad cap All you've proved is that the old thermostat isn't the problem. Same for the new thermostat. I'm betting on exhaust gas in the coolant.
'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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