I also replied on SVT, but since you don't have any responses...

You want the thermostat on top. Evans put it there for the same reason most every manufacturer does; the cooling system temps are better controlled when the hot coolant operates the radiator inlet, instead of the outlet. Throttling the outlet with the thermostat can be misleading because the upstream side is constantly being cooled in the radiator, making the thermostat operate as if the engine is also seeing these cooler temps.

 

I also replied on SVT, but since you don't have any responses...

You want the thermostat on top. Evans put it there for the same reason most every manufacturer does; the cooling system temps are better controlled when the hot coolant operates the radiator inlet, instead of the outlet. Throttling the outlet with the thermostat can be misleading because the upstream side is constantly being cooled in the radiator, making the thermostat operate as if the engine is also seeing these cooler temps.

this is exactly right, but there must be some cost or hidden reason because the other 2 cars i own (GM) both have thermostats mounted to the lower outlet. it does not make any logical sense, except that maybe its cheaper to install there.

 

Ford (and apparently GM) must have something in mind because I can't see why they couldn't have installed the very same thermostat housing in the top hose if they wanted to (and eliminate the bypass fitting on the coolant crossover). The t-stat bypass would run down and tee into the lower radiator hose...AHA! they saved one fitting by putting it on the bottom! Could it be that simple?

 

Mabye for emissions to get the car up to temp sooner?

 

...but until the t-stat opens, they would operate the very same way...with coolant bypassing the t-stat (therefore radiator) and returning directly into the engine.

 

My 2000 Lightning & the Ford GT have the thermostat at the top. The Ford GT has a remote stat with a hose from each head feeding it and one outlet from the stat to the hose/line feeding the top radiator inlet. Go figure???

 

From what I can tell it makes very little difference whether it's mounted in the top or the bottom. The by-pass is what controls the thermostat and has nothing to do with radiator. The only difference is that the by-pass coolant must travel a little further to heat the thermostat causing it to open. While it's closed the engine doesn't even know the radiator is there. Maybe I'm missing something here.