Sounds like a big fan turning on!
 

I noticed when pulling a load (11,000 lbs) up a steep grade it sounds like a huge fan turning on under the hood! Is it my cooling system fan or something to worry about??? Thanks in advance!

Was your coolant temperature hotter than normal? I am betting that it was. The stock fans on these trucks can pull about 25,000 CFM when engaged.

They are huge fans when engaged.

Nothing to worry about, it was working properly.

Not sure about the temperature at the time. It wasn't that long of a pull. I've heard it on long and short pulls up "steep" grades when I'm loaded down. Come to think of it I've heard it in short intervals running slow without a load, hmmm, the fan is that powerfull!
Good to hear it's normal.....Thanks!

Ive had my fan turn on and my temp is not much warmer then normal when towing my toyhauler. Mostly when going up hill also.