I have a 2014 Durango Limited with a V6 and 180,000 miles. The radiator fan only appears to run at high speed, even in the winter with the AC off, and is very loud when it is on. I replaced the thermostat, but this did not resolve the issue. I have checked both the low speed high speeed radiator fan relays by applying 12V and testing for continuity. Both relays appear to be in working order. What else could be causing this issue?