Brian,

I totally agree...T-stat rating is the minimum temp, the temperature the stat opens. Once it opens, the big husky radiator cools the water, sends it back to the engine and it sits, or circulates until the T-stat opens again and the whole deal happens again. If this T-stat happens to be a 190&deg unit, the temperature of the engine and cooling system would stay, under normal conditions, around 190&deg...wouldn't it?

Provided the radiator had the capacity, and you stuck a 170&deg thermostat in, the engine and cooling system would stay, under normal conditions, around 170&deg...wouldn't it?

If a person went into a parts store intent on buying a T-stat to keep their ride at 180&deg, would they have to do a bunch of calculating to guesstimate which thermostat to buy. I don't think so, I think they would merely buy a 180&deg stat.

If your rig runs for years at, say 190&deg, and all of a sudden, it starts to overheat at the smallest pull, or the occasional hot day, the radiator is the first place you would look. It is plugging up or the fins have rotted off and it can no longer cool the water below the minimum opening temp of the stat. This is how I have always pictured it working.

Stuart