My outside temps right now vary between 70º and 100º F in winter the car has seen as low as 10ºF temps were consistent with the old thermostat. The new thermostat is only a month old, so I'm not sure what temps will be like in winter yet. I suspect that if I let it sit and idle for 30 mins that it would probably get up to 105º C, the low speed fan would kick on, and the temps would start to drop, but I haven't done that. My car is an 03 R53 with 100,000 miles on it. It did get a new radiator and fresh coolant when it got the new thermostat as well. the old radiator had a slow leak. The thermostat housing was fine, but old.