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Found the post. As of 2/15/99 it was on page 5 of the Tractor Talk board. I cut it and pasted it below. It involves a John Deere, but I imagine the info is good anyway. Turf Boy: OK. Here's the scoop. The tractor was a '39 JD A. It did not have a water pump, but, as did all early JD A's and B's, depended on
"Thermo-Syphon" circulation of the coolant through the engine block and radiator. In order for this system to work, the coolant must expand (become less
dense) when heated (by the engine) so that it tends to rise and displace cooler material in the radiator. Circulation in the cooling system is thus obtained. Such
expansion is characteristic of water. This system was used with many early IC engines, including automotive. It requires an appreciable elevation difference
between the heat source (engine) and the heat sink (radiator). Also necessary is the use of a coolant which expands when heated (like water) to stimulate
circulation. Common antifreeze (ethylene glycol) is NOT (I learned!) such a coolant. In my case, I had drained the cooling system and then added a gallon or
so of antifreeze, followed by enough water to fill the system. The antifreeze entered the engine water jacket but, when the engine started to warm, did not
create circulation. Not suspecting a problem, I was not watching the tractor as I should have been. The engine got hot, no--HOT! After realizing what I'd
done, I let the system cool, then drained the system again. I allowed the antifreeze to mix with the water and put it back in the system. It worked OK after
that. I should add that the tractor was (is) a toy and I didn't work it hard at all. Undoubtedly, ethylene glycol does not expand on heating and thus impairs the
cooling activity (circulation) of thermo syphon systems. I found out later that JD recommended draining of their TS cooling systems during cold weather,
rather than the use of antifreeze. Now I know why!
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