Ran up to the nearest food mart yesterday, 20 miles away, and developed a serious leak in the "water tube" that runs front to back (or vice versa) on the right side of the engine. The leak was spewing water. In order to get back home, I removed the radiator cap and drove the 20 miles back home. The leak was a drip, drip, and it ran at it's normal "cool" temperature all the way back home and I calculate it "lost" about 1/2 gallons of coolant. So long as I:

1.) keep coolant in the system, and;
2.) get no indication that the engine is running hot,

what are the dangers until I can get this thing properly fixed?

(Please remember that I live 60 miles from the nearest town, mechanic, parts store, or salvage yard, and that transportation to any of those for any reason is ... difficult, at best.)