How much coolant to drain when replacing thermostat?
 

How little coolant can I get away with draining when replacing the thermostat? I know I've got to pull the hoses on the thermostat housing, and also loosen the bracket that holds the water pump. If I just drain a half gallon or so via the radiator plug, will that be enough to prevent a gush of coolant?

I just flushed it and put in all new coolant in yesterday. Then today I hooked up the Torque app to my bluetooth OBD II adapter and saw that it's getting up to 230 F while idling (vs ~210 while driving in the city). Granted, the ambient temperature was 97 F and the AC was on, but I'm thinking 230 is still too high. I should have looked at the temperature before I flushed the coolant. Lesson learned.

Alternatively I suppose I could just drain it through a t-shirt into a clean pan or something, then re-use it. What's my best bet here?

I just drain it all, it would be easier refilling it entirely than it would be too bleed out the same amount of air that you'd introduce.

Just drain into a clean bucket and reuse it all, unless it's chunky there's no need to filter it with anything.

Thanks