Are you saying that a car in open loop will behave differently depending on the thermostat that is in it? Open loop is open loop, or am I missing something?

What kind of radiator do you have? Is it different than stock?

 

your missing something.

your stat is a valve that opens and closes with heat and cooler temps.
as heat rises the stat opens, the cooler water in the radiator will now flow through the motor
cooling it down, as the motor cools down the stat will close, holding the water in the radiator
cooling it off more for the next cycle.

if the stat is wide open, aka full loop, the water is running through the radiator and not cooling down enough, this increases the chance of running hot and or over heating the motor,
due to stat failure or being stuck in traffic.

the stat is a spring loaded, pressure open valve, as heat causes air to expand inside the valve will open, as it cools the air will contract and the spring will close the valve.
if this valve stays open all the time, the little amount of air inside the valve that makes it open will leak out over time from constant pressure, until it does not open any more.

my radiator is stock.

 

The stock temperature gauge is no where near accurate if that's what you guys are going by. I'm running a modded 03 stat and it's about 190 "according to the gauge" but I'm not sure what it truly is.