The Diesel Stop banner

ENGINE FAN AT 70+ MPH

7K views 7 replies 4 participants last post by  EpicCowlick 
#1 ·
I know have 1550 miles on my new '11, I have a question to other owners. At 70+ mph (no load factor other than the weight of the truck)the engine fan comes on and stays on untill you drop below 65-70. My concerns are as this happens the fuel mileage drops 2-3 mpg on the guage (it actually gets better mileage in town vs. highway), what is going to happen when the ambient temp gets above 40 degrees (so far it doesn't matter if it is 20 or 35 degrees the fan comes on). I have called the dealer they dont know anything other than bring it in and we will hook it up to the computer. Wanted to know if I have a problem or it is just normal even though it doesnt seem that it should be doing this. I just joined this site, I have been reading it for years but never had a concern to discuss that I couldnt find the answer for.
 
#2 ·
I have never noticed anything different sounding at speeds over 70 mph. How do you know the fan is coming on? On my 2005 it was obvious when the fan fully engaged and it rarely did. I live in South Florida, not exactly cool temps either!

I get better mileage at slower speeds and yes over 70 seems to drop my mileage 2-3 MPG over going 55-60 mph. I have logged almost 10k miles in two different 2011 6.7's and they have been very close MPG wise, despite one being a SWB F250 and the other is a LWB F350. Unfortunately, these are non-aerodynamic bricks driving down the road.

FWIW, I seem to get around 15-16mpg at 70 - 80 mph. What are you seeing?
 
#3 ·
I am 95% for sure that the fan is engaging as when you let off the throtle the fan noise slows down/decreases, the mileage drops from 16-17 to as low as 13.4-15. On my 6.0's it had to be hot day pulling a load or a long grade to get the fan to lock up and run where you could hear it over the engine. I understand the aero issue at 75-80 mph but the fan should not be coming on especially at the ambient temps we currenlty have.
 
#6 ·
I am 95% for sure that the fan is engaging as when you let off the throtle the fan noise slows down/decreases, the mileage drops from 16-17 to as low as 13.4-15. On my 6.0's it had to be hot day pulling a load or a long grade to get the fan to lock up and run where you could hear it over the engine. I understand the aero issue at 75-80 mph but the fan should not be coming on especially at the ambient temps we currenlty have.

Ditto on my expereince with a 6.0 too... I would take Epic's advice and have the dealer check the fan clutch. 13.4 mpg at 70 mph is out of the range of what most of us here are seeing running empty. 15mpg is at the lower end of "normal" imho. I gotten down to 15mpg on the computer after I have just reset it and a regen has kicked in...
 
#4 ·
something may be blocking the flow to the radiator, a plastic bag? maybe!, at those speeds there is plenty of airflow and the fan should not come on unless there is a bad temp sensor or blocked airflow!
 
#7 ·
GOT IT FIGURED OUT

TURNS OUT THE FAN/CLUTCH WAS BAD, REPLACED AND ALL IS WELL. MILEAGE BACK UP TO 17.8 YIPPY
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top