I would suspect the radiator has internal buildup preventing good heat transfer. The fan kicks in at 110 because it is the last effort to stay cool. Its not needed at 90.

Two things cause the fan to run. First is engine temp. Second is the high side pressure in the AC system. If either is too high the fan should run.

I agree I have read several threads stating higher temperatures than what I am use to seeing. So Im not sure I have a good answer for you

Did it always run this hot ? Or is this a recent development.

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I got too many cars!! Insurance eats me alive. Dave

78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k