in one of my cars (1968 Camaro) I used the autometer 3654 water temp gauge (link at bottom of this post) to monitor temp, and as it is already configured to activate two different functions at two different threshold of your choice, I chose one ot light up my idiot light at 188 degrees (my choice) and the other one to start my cooling fan at 194 (my choice again). You can change those thresholds at any time, I do so when going at a bumper to bumper cruise for obvious reasons.
https://www.autometer.com/2-1-16-wat...-fse-3814.html