But the engine did not have this overheat problem before I started the flush and refill. Nor did it overheat while I drove it 100 miles with the citric acid flush and no thermostat in the cooling system.
Plan for later today is to drain the antifreeze mix, remove the thermostat and refill with just water. That should take me back to the conditions I had last with no overheating. While I'm at it, I'll pull the sensing bulb from the rear of the head and test the mechanical gauge against my cooking thermometer.
By the way, the radiator has a 7# cap, which should raise the boiling point of 50/50 antifreeze mix to 245F.
On my original flushing with water and later citric acid the coolant drain at #6 cylinder new did "clog up" so much that it stopped draining. Mostly just slowed down a bit and gentle twisting of the handle would resume "full flow".
'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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