It's very simple. IF the radiator is optimal for the vehicle and combination, it will cool the coolant faster than the engine can heat it. I'm not just arguing theory, I PROVED it through my own experiences. Once with my 75 Ford F250. With no other mods, I flushed the system and installed a high flow 160 thermostat. The temp gauge barely moves off the first line, and it's right. Coolant coming out of the engine is about 170* and goin into the engine is about 88*.
With Vixen, once I installed a high flow 160, her temp coming out of the engine is about 167* and going into the engine about 79*
The two radiators in those vehicles slap GET IT DONE and that's the the key. Having the most efficient radiator possible. The reason for the 160* thermostat is this. If you allow the engine to get to say, 190 or 195, there's not much "cushion" before it reaches what I call the point of no return. That's when the cooling system just gets maxed out and cannot shed heat anymore. It's a little different for each cooling system, but once reached, the engine just keeps heating up. So, if you open the thermostat earlier, you don't allow the engine to get to that point.
The reason for the high flow thermostat is exactly what we're discussing. Getting the coolant out as quickly as possible. If you find yourself having to allow the coolant to stay in the radiator longer, it's because the radiator is not doing its job for "whatever" reason. Not big enough, partially stopped up, or "whatever". A good optimized radiator that does its job efficiently will shed heat very quickly and allow that coolant to get back into the engine so as not to allow the engine to reach the point of no return.
Generally speaking, a stock to mild engine is not as "picky" when it comes to everything working in conjunction. But when you couple high compression, a big cam, lots of initial timing all in a small compact space with a small frontal area for air flow, you need to optimize each and every part of the cooling system, and leaving the coolant in the radiator too long does not achieve that. Hope all of that made sense.
