Model M John Deere, lower radiator hose cold?

[RickB]

If you did actually add a full gallon of fluid to this system, it's more than likely that before you did there wasn't enough in it for any coolant to circulate at all.

 

[psychonautbuddy]

I overfilled the radiator with the intention of draining off, at the bottom, a portion of the coolant, to inspect for sediment, of which, there was little.
Although the upper neck was perhaps half covered, I don't think this precluded therm-siphon, although I might be wrong. After filling, I discovered
a tiny crack on the upper cast iron neck, at the top half of this neck, leading to the upper radiator port. It seems a very small amount of coolant is
weeping at this spot, so eventually, I am going to have braze or jb weld this area.

Another item, which perhaps I should start another thread for, is that the throttle will not stay in position, but drifts down, so I am constantly having
to move it towards vertical, especially when powering thru stands of woody brush. I don't know if this is a design feature, or if I am asking too much of the engine.
I do most brush hog work in 1st gear, and grass is mowed in 2nd.

 

[RickB]

If you initially had coolant halfway up the upper hose neck, you are correct in thinking it was enough to thermosyphon. Your throttle issue is related to a spring loaded friction disc somewhere in the throttle linkage, probably at the hand lever pivot. Not enough spring pressure, or a failed/faulty friction disc. Should be a cheap and easy fix once you locate the mechanism.