Do I have to drain my coolant to change the thermostat. I have a 1972 with a 350 and the t.s. is right on top. My Haynes book says to drain but I can't see why I would need to do that. The only thing I could imagine is that some of the coolant might leak out of the hose when I take it off. Any experienced insights would be great. Thanks.

Not a total drain but you'll need to remove enough coolant to lower the level below the thermostat you're replacing.
It's more than you think...;)

Thanks for the words of wisdom. I really hate cleaning up antifreeze. I guess I'll drain some.

After all is said and done. Your going to loose coolant no matter if you drain enough to get below the stat or if you just remove the stat without draining.