My 93 300e stays just above the 80 mark almost all the time. I have to be sitting for quite some time (5 mins or more without moving) after driving and it being up to operating temp before it goes anywhere near the 100 mark, and never hits it or over. My A/C hasn't worked in the last 2 years, so no auxillary fans on. Only time I had ever heard the aux fans come on was late last year when it blew the headgasket and overheated, and at that time it hit the red line before they ever came on. Just something else other than the t-stat, did you get the system flushed after the head rebuild? Seems minimal, but there could be a bit of trash inside the ports or in the radiator from when it sat for a bit.