The radiator is what cools the water, the t Stat only opens to allow the water to flow through the engine. If your radiator is plugged nothing will help until you clean it out or change it out. A lower t Stat only works if your radiator is cooling efficiently. If you go too cold it will cause problems also, the engine needs certain temps to function efficiently. If your radiator is in good shape it should cool the water to 150% ambiant temp (30°to 40° below the t stat temp). If your engine is modified and the radiator won't cool it low enough you need to upgrade the radiator until it does. This is assuming your fans are working properly and this is a driver car not a race car, things change for racing.

 

I know this. I'm just being lazy. I've done so much work on this car, I need a brake. The way it works has been that way for 3 years. And as long as it does not overheat I can take care of other issue it has.
I was just making a point that putting a lower stat, in my case, has not made any significant change in how the motor operates. (In My Case)

 

old thread I know...my car is same way,put 180 therm,didn't help...pulled drain plug and nothing came out till I put air into it from below..flushed and no rust at all...hmm..radiator time.