Compared to a gasser, the engine temps won't go up very fast when you get on it. Diesel engines are much more efficient and with the big radiator you probably won't even see a change in the temp. I have rarely experienced the fan engaging on my other two trucks. When they did, I was usually sitting at a light, 100* outside with the AC running. The fan would engage until I got up to about 20 mph and then it would go off.