rad and coolant,

[Dave Williams]

-> Do You really need something as tight sealing as a ball valve?
-> I would think a butterfly valve would be fine and take less torque to
-> operate...

 A butterfly valve would be fine, but all the commercially available
valves I've come across of appropriate size - 1-1/2 to 1-3/4 inches -
have been ball types, except for some of the old zigzag faucet types
which would be useless.

 Do you have a source for butterfly valves that size?  Remember they
have to handle water at up to 250F and 25psi without drooling around the
shaft.