The Stovebolt Site Forums The Shop Area Engine Shop Help with Overheating problem (1952 GMC 228)

It's been 5+ years since I flushed the cooling system on my '52 GMC 228.

I bought 2 gallons of antifreeze, 2 gallons of distilled water and 5 pounds of citric acid powder.

Parked the truck nose down about a foot in the driveway and then drained the old coolant into a 5 gallon bucket. Got about 4 gallons as expected.

Connected the garden hose to the "flush fitting" I put into the return hose from the heater the last time I flushed the system.

Removed the thermostat and put the thermostat housing and upper radiator hose back in place. Left the drain cocks in the lower rear of the block and in the lower radiator hose open and the radiator cap off.

Cracked open the temp sensor fitting at the rear of the head to allow air to escape. GMC engines are known to run hottest at the rear of the head. When I bought this truck it had modern aftermarket gauges that sort of looked like stock, but were very hard to read accurately, especially oil pressure and coolant temp. So I installed a 270 degree sweep mechanical temp gauge at the rear of the head and moved the electric gauge's sender to the engine side of thermostat housing. Historically, the gauge in the head has read about 10 degrees hotter than the gauge in the thermostat housing.

(This is paragraph A) Refilled the cooling system with just water from the garden hose, then adjusted the hose flow until it barely overflowed at the radiator filler. Fiddled with the drain cock at the rear of the block any time it would partially clog. Let the hose run like this for 10-15 minutes. Then started the engine at about 1000 rpm and let it run another 15 minutes with the hose flow adjusted to keep a slight overflow out of the radiator filler. Shut the engine off. Allowed the system to drain all the way down and repeated this paragraph one more time.

Closed all drains, mixed the citric acid with 5 gallons of water and filled the cooling system. "Burped" the temp sensor at the rear of the head until only liquid came out, then tightened it up.

Drove the truck for about a week. Never got over about 170 degrees (A/C on, 90F air temp, NO thermostat). Maybe 100 miles total. The longest was 30 miles to the dump to dispose of the old coolant.

Drained the citric acid mixture and did the flush with water routine as noted in paragraph A above.

Drilled a 1/8" hole in the flange of a new 160 degree thermostat and installed it. Closed all drains, mixed the 2 gallons of antifreeze with 2 gallons of water and filled the cooling system. "Burped" the temp sensor at the rear of the head until only liquid came out, then tightened it up.

Then started the engine at about 1000 rpm and let it run. "Burped" the temp sensor at the rear of the head again. Checked both the coolant temp gauges after 2 minutes. They were both starting to register. Started picking up tools. Felt the upper radiator hose. It was starting to get warm. The next time I looked at the temp gauges the electric temp gauge it read about 150-160 degrees. The mechanical gauge at the rear of the head read 230 degrees and climbing!

Shut the engine down, said a bunch of words I wouldn't have said if my mother was standing there, cried a bit and gave up for the day.

In my mind only 2 things can be wrong.
1. I put the thermostat in upside down. I do know the difference.
2. The thermostat was defective when installed.

This morning I took the thermostat out. It had been installed in the proper direction. Then I suspended it in a pot of water on the kitchen stove and warmed it up, testing the water temp with a cooking thermometer. It started to open at 162 degrees and was completely open at 170 degrees. It is stamped 160F.

What now, oh temple of knowledge, aka 'Bolters?????