C15 kenworrth t600 red alarm

...200 is not that bad going uphill , probably computer set up this way to avoid issues with drivers who doesn't care or pay attention

 

A C15 won't engage fan for engine temp until 217 degrees and that setting can NOT be changed. I forget what temp sets alarms but I'm guessing around 225?

KW may setup different than peterbilt, which I am familiar with. But there's likely two temp sensors. One for gauge and dummy light and one for ecm.
It's pretty common for the gauge to be very inaccurate.

As far as fixing your problem I'm not sure. Could replace the temp sensors. Or just turn the fan on manual when climbing hills.

I watch my temp close and turn fan on at 200. I run a scangauge and can see the temp the ecm is reading. My gauge in dash is worthless