Fan Clutch on and off

[BigO]

I noticed on vacation that at 60 MPH vs 70 MPH that the fan clutch kicks in more. This is pulling a 9,300 lbs 5th wheel in 111 - 116 degree temps.

The state of CA posts a 55 mph when towing so we ran 60, AZ is 75, we ran 70. All flat land and that clutch was on and off every 8 - 10 miles at 60 and on and off every 20 - 25 at 70.

MOre air flow is what I would guess, however the engine is working harder at 70 vs 60. Anybody have any ideas. Truck is stock!

Anybody else notice this?

[Lone Eagle]

My truck likes 2000 RPM best pulling 10K. (65-68)Under that and over seems to work it more. Later! Lone Eagle ;)

[FisHn2DMax]

At those outside temps, I'm surprised that it didn't kick on more often LOL.... If you had a boost guage, you'd notice the higher turbo boost is required to maintain 70 MPH while towing on flat or hill. Also, you're right on about more air coming through at the higher speeds, but many other factors also come into play: Air density, humidity, Altitude, Etc. From what you described, your truck seems to be operating perfectly normal.

[BigO]

Thanks for taking time to read and reply.