I know that the controversy over whether to use a low temperature thermostat gets almost as heated (pun intended) as which oil to use, but here goes.
When I first read about the low temperature thermostat, I wasn't convinced. I figured the thermostat really did not make much of a difference, since the coolant temperature is really limited by the capacity of the radiators and the temperature at which the fans go on. But after reading way too many posts on the subject, and most recently the Hartech article (see below), I went with the Wahler 160 thermostat.
What really convinced me was the inherent flaw in the 9X6, 9X7 cooling system, namely, that the thermostat and the coolant temperature sensor both receive coolant only after the coolant has gone through the radiators, coolant that is is at its coolest. The hot coolant exits the motor, goes through some long plumbing to the two radiators up front and back through some long plumbing before it reaches the thermostat and temp sensor, nice and cool. But the coolant around the cylinders and heads will be much hotter than what the temp guage reads, because the temp guage is reading coolant that already went throught radiators.
In addition, the stock thermostat begins to open at 86 C and is fully opened around 99 C, so the thermostat is partially opening and closing when the coolant is almost at the boiling pioint. And remember, that is coolant that is already gone through the radiators and cooled down. The coolant in the motor around the cylinders and heads will be hotter than the coolant going into thermostat.
So what happens? You are on the open road with sparse traffic, going a leisurely 75 miles an hour in fifth gear. Because of the very good airflow at that speed, the radiators are working at their optimum, and the coolant is cold enough so that the thermostat is closed, or is partially closed. So you decide to downshift to third and get on it, to pass a car, or just for the fun of it. The moment you open the throttle and start approaching the redline, the cylinders almost instantaneously get significantly hotter. But the thermostat is partially closed, impeding the coolant flow. More more important, the coolant that is trapped around the cylinders and the heads was already significantly hotter than what the temperature gauge reads, and getting hotter by the second. And since the hot coolant in the engine has to go through all of the cooling system plumbing and the radiators before it gets to the thermostat, there's going to be a significant lag time before the thermostat opens fully to allow the full flow of cooler coolant to get to the now very hot (and getting hotter) cylinders and heads. What you now have is a condition that is perfect for a localized hotspot in the cylinder or heads.
With the low temperature thermostat, the coolant flow in the above situation will always be at its maximum, since the thermostat will be wide open at cruising speeds. So that when you cane the motor, you are getting the maximum flow of cool coolant over the rapidly heating cylinders and heads. The low temp thermostat ensures better cooling during a high load, high temperature acceleration, which after all, is what our cars are all about, right?
So that's my story and I'm sticking to it.
http://www.hartech.org/docs/buyers%20guide%20web%20format%20Jan%202012%20part% 205.pdf