Let me see now, when it is hot outside and I am chillin with ac and towing a heavy load up a long hill on hiway (like I did a few weeks ago when it was 95 out) am I worried about losing 5hp (give or take) for cooling fan? Not at all, my first concern is it stay cool. I have yet to get my 2000 K3500 to brake a sweet no matter what I do. I can stop is traffic on a 90 plus day with A/C on towing a heavy load and the tempature never climbs. (it is impressive) It has a factory HD system with a 10 bladed clutch fan that does its job when needed.