NA the 180* T-stat from O'reilly's is what I like to run. Should be tuned if you're changing temps on T-stat, and let the tuner know what temp so they can adjust your fan operation accordingly. I don't see an advantage going below 180, except for a track car that is trying to maximize a single pass. Even with a 180 T-stat my cylinder head temps show 190 normally. On a hot summer day in Vegas, 195-198. With the AC blasting, 200-205. A higher temp T-stat is actually going to cool coolant more efficiently by being able to throttle coolant flow and allow hot coolant to stay in the radiator longer while the cooler coolant absorbs as much heat as it can before flowing to the radiator. A lower temp T-stat is going to be wide open all the time passed it's designed operating temp, free-flowing the coolant through the radiator as fast as the pump wants to push, giving less time to bleed off heat. The only way to take advantage of the free-flow is with a higher capacity radiator, and/or more cores. In either situation, more capacity will yield better cooling regardless of T-stat operation. OEM is the safest choice, but I've had no issues with my 180 NA or FI.
