The engine/coolant fan on my 2108 2500 6.7 (18k miles) seems to be cycling on and off when it is not really needed. For instance, it runs when I start the vehicle after sitting for days. While driving it'll cycling on and off at ambient air and coolant temperatures when I would not expect it to be coming on at all. Not sure what's going on. No codes are thrown. Started doing this a few months ago. I was under the impression it was only supposed to come on when coolant temp hits 217 degrees. Any insight will be appreciated. TIA