I am on thermostat #3 and this one makes my temp guage read 90C. It is a dealer thermostat. As a pessimist, I may conclude that this one opens early and is hiding a problem Previous two Wahler t-stats read 98C on the freeway. Has you car ever had dexcool? Do you have brown sewage like material lining your connection from the upper radiator hose to the block?

Brian