I used to have a 180 degree stat in my Grand Am, which came factory with a 195. I have no way of reprogramming the fans, so the lower temp stat did absolutely squat in the summer, still ran at 215 in stop and go. However, in the winter time, my milege was absolutely gone with the 180 degree stat. I was actually running around 170-175 with the heater on full blast (confermed with Tech 2). Also, it didn't run very good at all, and when I changed the oil on cold days, even with the car at temperature, the oil didn't even burn me. I recently switched back to a 195 degree stat. My milege, power, and smoothness are back, and when I changed my oil 3 weeks ago it was actually hot to the touch. I just changed my plugs also, they were absolutely blackened with carbon and crud, a sign of way too much fuel in the mixture. Stock temp thermostat is best IMHO, even for high performance. As long as intake temps are ambient, coolent temps of 215 -220 are still good for power if you aren't getting detonation. Heat = power