MPG fall off recently - Cold Weather related?

[Scapino]

The MPG on my '21 Outer Banks is starting to fall off and I don't know why...

I always kept an eye on my MPG (typically around 29 - 30mpg) but I recently started a new job with a 75 mile one-way commute. Ouch, I know. 90% of the commute is highway. Southern NH to far west of Boston, so unless there is an back up or something, I'm typically able to do 65 - 80MPH most of the way. During the first month of the new job I was getting right at 30mpg. I have to fill up every two days (and trust me, gas is way cheaper in NH vs Mass). But suddenly my MPG dropped off to 26mpg. And it's not just the MPG - the 'Miles to Empty' gage also showed a decrease. Normally when I'd refill it would be about 440 miles to empty. Now it calculates 410 miles to empty (after a refill).

I thought maybe I'd gotten a bad tank of gas (I did stop at a new station). But after 4 refills at my normal Mobil station the MPG has not returned. The only thing I can think of that would cause this is that the temps have consistently been below freezing recently. Would the cold temp affect MPG that much?

Background notes:
New tires & brakes just before I started the new gig.
When I started the job I had 40k miles on the Bronco. The MPG fall off started around 50k miles.

Thoughts?

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[coopny]

This is pretty normal and not just in the BS. Department of Energy:
Cold weather and winter driving conditions can significantly reduce fuel economy. Fuel economy tests show that, in city driving, a conventional gasoline car's gas mileage is roughly 15% lower at 20°F than it would be at 77°F. It can drop as much as 24% for short (3- to 4-mile) trips.

Cold weather effects can vary by vehicle model. However, expect conventional gasoline vehicles to suffer a 10% to 20% fuel economy loss in city driving and a 15% to 33% loss on short trips.

You're reporting a drop off from 30 to 26mpg, which is a drop of ~13.33%.

One thing I'd point out is also speed effects MPGs, and more than people think. Doing ~70mph is going to net you around 2mpg more than ~80. Most cars are most fuel efficient around 55-65mph with severe drop offs in fuel economy above 70... of course, it's up to the individual driver to weigh which matters more, getting to their destination more quickly or fuel economy.

 

[tjbronco]

Maybe I can help give you a point of reference. I have a Big Bend 1.5 - for 2 years now. I have a 70 mile round trip commute (half of yours - been doing it 15 years) - plus have to drop off and pick up kids before and after. My commute (Cleveland Area) is around 2/3 highway and 1/3 downtown city. The highway I drive is marked for 60mph speed limit - I run around 67-68 on cruise control. I run Eco mode most of the time (I think Eco mode assists the driver in getting better MPG - does not make the car get better MPG - I am sure you can get bad MPG in ECO mode if you try). My car tends to average (per the dash gauge) above 30mpg during the warmer months (usually 31) and drops to about 29 during the winter months. I idle my car for a few minutes in cold weather so that my oil is a bit warm and I have some defrost action available before driving.
I would be suspect of the new tires and/or the mention of 80mph speeds - I have not driven my Big Bend at 80 for any length of time - but I would bet the aerodynamics do not do the MPG favors at that speed.

 

[Bronclahoma]

Could be the switch to winter blend gas. It helps your car start in cold weather, but decreases mileage. On the bright side, it's cheaper to produce. I doubt all of that is passed on the the consumer, though.

 

[Bluejaye]

Winter gas blend, it makes the mileage go down.

 

[Goodland]

Winter gas blend for sure. Also possibly more condensed air = more fuel burning. Used to call it turbo weather when it started to cool off after winter. I always found it a little tougher to keep my foot out of the gas pedal when the turbo was so eager to spool.

 

[Mark S.]

Also possibly more condensed air = more fuel burning.

Hmmm. Colder air is higher density than warmer air, which means you get more oxygen molecules in the same volume of air. More oxygen means more power if you ALSO add more fuel. But colder air shouldn't affect fuel economy. The computer can certainly add more fuel to higher-density air to provide more power, but only if you demand it by stepping harder on the skinny pedal.

Physics is physics: You need a given amount of power to accelerate at a given rate, and a given amount of power requires a given amount of fuel. You can make more power with colder, higher-density air at the cost of more fuel, but if you don't USE the additional power available--i.e. you accelerate at your normal rate--fuel burn will not change.

EDIT: Corrected a slight error. Denser air makes more power because there are more oxygen molecules in a given volume.

 

[Goodland]

Hmmm. Colder air is higher density than warmer air, which means if you can get more of it in the cylinder you'll get more power. But it shouldn't affect fuel economy. The computer can certainly add more fuel to higher-density air, but only if you demand more power (step harder on the skinny pedal).

Physics is physics: You need a given amount of power to accelerate at a given rate, and a given amount of power requires a given amount of fuel. You can make more power with colder, higher-density air at the cost of more fuel, but if you don't USE the additional power available--i.e. you accelerate at your normal rate--fuel burn will not change.

Yup yup, I was worse at keeping my foot out of it and likely used more fuel because the power felt good. So maybe some slight driving style changes are contributing in addition to winter blend.

 

[Escape2Bronco]

Normal. Lived up north all of my life. Gas milage drops in the winter. Many reasons like warming the car up and getting 0 mpg, winter blend, everything is stiffer adding to more friction requiring more power.

 

[BLUEOVALRACER]

If these 1.5 and 2.0 Eco Boost engines are like the 3.5's in the F-150 many guys say the plugs should be changed around the 40,000 mile mark not what ford says!!The engine being Turbo charged the boost can cause the plug gaps to close up smaller!!

 

[Cage1970]

Completely normal. Happens in every vehicle I’ve ever owned. I’m in Eastern Canada so we have real winters. Summer is 9.6L/100km and winter is 11L/100km

 

[Mark S.]

many guys say the plugs should be changed around the 40,000 mile mark not what ford says!!

Did they provide any data, or just opinion? Ford sells spark plugs through its Motorcraft division, giving it a very good reason to suggest shorter replacement times, yet it doesn't. Ford's recommendations are based on data.

 

[Webini]

Check your tire pressure. Cold air = lower pressure = increased rolling resistance = lower mpg.

 

[wireman]

I noticed your BS is a 2021. Is this your 1st winter with the vehicle? If not, how did any other winters compare to this one.

All the posts here give valid reasons for the decrease.

I'm on the wagon of 80mph, winter blend and tire pressures.

 

[KidWiff]

I’ve found the same with my BS here in Connecticut, in colder stretches. I wouldn’t expect THAT much of a difference, but I care anywhere from 2-4 mpg

Also, I find the mpg calculated by the vehicle computer is also off 2-3 mpg compared to what I calculate at the time of fill up. (Same station, same pump the vast majority of the time) but still the same 2-4 mpg difference in cold weather

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