Compression Ignition Addict
Join Date: Apr 2010
Location: Las Vegas Baby!!
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You have posted in the 6.7 forum but your question applies to any diesel pick-up so here is your answer. (IMO)
The fan clutches are temperature controlled. When the air flowing thru the radiator is coming out too warm, the fan will sense this and "lock up" which pulls more air thru the radiator to better lower coolant temp. This is a normal cycle and tells you your truck is doing exactly what it is supposed to be doing.
You will not normally hear the fan clutch when driving level or unloaded. The air flow thru the radiator at speed will be adequate to cool the coolant and the fan clutch is not needed to lock up.
Once you begin climbing a hill some things change. First is the engine is putting out a lot more power. Often, it is putting out maximum power (full throttle). Higher power output means higher cooling requirements. Secondly, the ground speed drops which lowers the amount of air passing thru the radiator naturally.
With lower air flow and higher cooling demand, the fan clutch engages to pull more air and this is the sound you hear. Just the way Ford, Dodge and GM designed it to do.
With a F350 diesel and only 3600 lb. trailer I would say you could drive any speed that is safe for conditions.
You will know when your fan clutch has malfunctioned when the truck is overheating. As long as you hear the clutch cycling, and the temps are good, drive it any way you feel is safe. Safety first when towing loads!!!
2012 F450 Ultimate Lariat pkg, 4X4, FX4, 5th wheel prep, camper pkg, 40console40 seat, Ingot Silver and Black guts
Reese Elite 18k 5th wheel
DuraFlap flaps all 4 corners
60 gal aux tank in bed
7.4 mpg as shown @ 70mph and 25740 lbs gross!!
2012 Fuzion FZ310 Monster Edition Toy Hauler 12,500 dry 16,500 loaded to play. 3100/3500 pin weight
Breast feeding is a hard habit to quit