An hour + later ...

Refill with water only, burp the rear temp sensor to clear air from the system and start driving it around the neighborhood. 100F air temp. No thermostat.

Engine temp stabilized at 178F at the rear of the head after about 1.5 miles of driving. The rear gauge had been tested earlier and found to read about 7 degrees high between 180 and 190, so this 178 indicated was more like 172 real. Front temp gauge read somewhere around 170.

Drove a total of 4 miles and neither temp gauge changed a bit. When I turned the engine off the rear (mechanical) gauge peaked up to about 192-195. This truck has always done that.

Plan now is for another trip tomorrow morning, maybe 10 miles or so. If that goes well I'll put in a thermostat (probably the old one) and test some more. If THAT goes well, maybe put in new antifreeze over the weekend.

I'm kind of up against a deadline here. The truck is supposed to represent the Gillespie County Historical Society in the 4th of July parade next week with a bunch of kids riding in the back and the Big Kahuna of the GCHS riding shotgun. But I won't risk a breakdown or overheat during the parade.

'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.