Mileage tanks after update

[dejones64]

Those getting over 28mpg, still stock tires or did you change to AT's? I replaced the stock continentals on my BB 1.5L to 245 AT's at the dealer before picking it up. In the summer months I struggled to get 28mpg. Winter I'm around 25mpg. Pretty much in Normal mode (no different in Eco). Running 92/93 octane.

I'm guessing the bigger/heavier tires is my constraint.

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[davidhluther]

I’m sure I need to get it serviced, but this has been my experience at about 13k miles. 25ish driving moderately in the beginning that dropped to 22ish in my BL+BL after I got that damn bug screen/deflector thing and a Yakima rack on it. I was using the rack often and have had the time to get the screen/deflector removed.

But last week, I drove about 400 miles each way from NC to SC — 15mpg on the highway in Eco doing 80mph. My average MPG for each trip was 16.8 and 17.1.

Something has got to be wrong, right? I anticipate a mileage drop because of the resistance from the cosmetic add-ons, but I get better city mileage… and there’s no way I should be get Hummer mileage on the highway.

 

[rdc17]

I’m sure I need to get it serviced, but this has been my experience at about 13k miles. 25ish driving moderately in the beginning that dropped to 22ish in my BL+BL after I got that damn bug screen/deflector thing and a Yakima rack on it. I was using the rack often and have had the time to get the screen/deflector removed.

But last week, I drove about 400 miles each way from NC to SC — 15mpg on the highway in Eco doing 80mph. My average MPG for each trip was 16.8 and 17.1.

Something has got to be wrong, right? I anticipate a mileage drop because of the resistance from the cosmetic add-ons, but I get better city mileage… and there’s no way I should be get Hummer mileage on the highway.

That seems way off. I get around 25-26mpg driving 70ish on the highway with the AT tires.

 

[Mark S.]

But last week, I drove about 400 miles each way from NC to SC — 15mpg on the highway in Eco doing 80mph. My average MPG for each trip was 16.8 and 17.1.

What kind of rack? Adding to vehicle height increase aerodynamic drag, so adding certain types of racks will absolutely adversely affect fuel mileage, especially at higher speeds. The amount drag increases as a square of velocity, which means power required increases as the cube of velocity.

For example (these numbers are not representative of your car, they are made up for illustration), assume a car requires 10 hp to overcome the aerodynamic drag it generates at 50 mph. That same car will require 80 hp to overcome the drag generated at 100 mph. Doubling the speed quadruples the amount of drag, and increases the power required by eight times.

 

[GJarrett]

I’m sure I need to get it serviced, but this has been my experience at about 13k miles. 25ish driving moderately in the beginning that dropped to 22ish in my BL+BL after I got that damn bug screen/deflector thing and a Yakima rack on it. I was using the rack often and have had the time to get the screen/deflector removed.

But last week, I drove about 400 miles each way from NC to SC — 15mpg on the highway in Eco doing 80mph. My average MPG for each trip was 16.8 and 17.1.

Something has got to be wrong, right? I anticipate a mileage drop because of the resistance from the cosmetic add-ons, but I get better city mileage… and there’s no way I should be get Hummer mileage on the highway.

I hope I am not making a great leap into apples-and-oranges territory, but I am not surprised and have two thoughts about that.

Firstly, I once built up a 1999 4x4 Explorer which had the drag coefficient of a parachute - much like a Bronco Sport. Stock, increasing highway speeds caused a very significant drop in mpg... at 60 mph I could get 20 mpg, at 70 it dropped to 17 or less, and at 80 it went down to 13. Once I put the roof rack on and went above the speed limit on the highway I could almost watch the fuel gauge go down it got so thirsty.

Secondly, I now own a 2017 EcoBoost Mustang that just clicked over 100k miles and can testify that once EcoBoosts stay on the boost, they suck fuel every bit as much as a much larger engine. It takes fuel to feed horses and at 80 mph you are going to be feeding all those horses all the boost they can gulp full time. At lower speeds the boost goes down and/or even off for a lot of the time. I recalibrated my Mustang's fuel monitor to be accurate (all Fords that I have owned have always been a little optimistic on mpg; true mpg is always a couple or few mpg less than what the readout displays). I live in Florida and feed the Mustang premium 91-93 octane fuel. At 50mph on near sea level elevation flat roads and no boost it gets an honest 39 mpg (that is not a misprint and surprised me as much as anyone). It gets 35mpg at 60mph and 31 at 70mph (this is on flat roads and roundtrips to negate wind variances). At 80mph, even with the good drag coefficient of the Mustang, the boost stays on full time and the mpg drops down to 23-24mpg. That's about a 25% drop in mpg compared to 70 mph and a 33% drop compared to 60mph. Mileage goes down further in hilly terrain: I lived in Greenville SC until two years ago and the mpg's were not as good there as in Florida.

I don't own a BS yet - it will be my next vehicle - so I don't know much about Eco mode, but at 80 mph if it keeps the engine out of boost then it probably struggles even more than with boost.

You drove 80mph in hilly Carolinas terrain and your mileage dropped 33% in a vehicle with a heckuva lot worse drag coefficient than my Mustang. Your experience does not surprise me one bit.

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