I also never had a problem with my Toyota. When I was stuck in traffic on a 100 degree day, the temp gauge didn't even budge. Mine stays smack in the middle and never budges. On a Mercedes ML-430, I remember it usually ran around 80 degrees Celsius. On a hot summer day, it would move up to around 100 degrees Celsius. I remember the first time it happened, I was panicing watching the needle inch up. But then again, it is a Mercedes.