I'm in the process of flushing the block now. Been doing it with the engine running for about 20 minutes. Petcock at the rear of the block and bottom of the radiator open, radiator cap off, flush hose attached to the fitting in the return heater hose going into the water pump. Adjusted the flush hose flow so radiator filler (highest point in the system) overflows slightly.
I'm leaving to go to the gym in 30 minutes. Before leaving I will turn off the engine and adjust the garden hose flow to barely overflow the radiator. Wont be home for 2 hours, at which time I'll start the engine again.
I'll probably use the old thermostat just for giggles the next time I install one.
'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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