Cause for significant drop in mileage in 2.7 L?

[Lil Red Broncette]

I get about a mile per gallon better fuel economy while cruising on the highway in Sport mode. I can get 20mpg going from LA to Tahoe. Go figure. I thought it was a mistake, or maybe I got a tailwind or something, but it's been consistent.

Somehow this doesn't surprise me. I've noted in these many speed automatic transmissions the shift is very aggressive getting into higher gear and keeping RPM low. Conventional wisdom being low RPM equates to fuel economy, but I find to sustain speed in the higher gear (lower RPM) that it takes more throttle input because there is poor gear advantage. On a naturally aspirated V8 with plenty of torque may handle that okay, but these little 4/6 cylinder they don't deliver the torque without boost. If sport mode does what I think and more easily down shifts into lower greater it maintains a better gearing advantage and doesn't need as much throttle input and may not even hit burst.

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[cricex]

Checked hoses and they're all tight

 

[Lil Red Broncette]

Using the truck's calculator and the mileage was awful even before getting into elevation. I reset the trip at the start of this trip and it was 13mpg immediately in Austin on the highway, not when I got to Colorado or starting to go up in altitude.

I would be tempted to do it old school. Fill up the tank, reset the tripometer, run the full tank and then fill it up again. Divide the miles by the gallons it took to fill it up. If you reset the average, compare what that average says against what you compute. I don't know that I would trust the MPG computation it comes up with. You can't go too wrong with the manual method, the biggest ambiguity was how full the tank was at the start vs how much you filled it the second time.

 

[Silver-Bolt]

Are you hand calculating of using the Bronco data?

 

[mountainbronco]

please also check your indicated speed and whether that is within 1 or 2 miles of actual (use your phone or gps to get a second reading). If your indicated speed is off, your modules may have the incorrect tire size in the code, so your MPG calculation would also be incorrect.

 

[Murph914]

It is easier than it ought to be to leave the engine running when you think its off. If you get a meal or something and leave it running the computer will knock your mpg way down.

 

[sergk]

I happen to drove from Austin to Breckenridge and back two weeks ago.

I normally cruise 5 miles over speed limit, basically a combination of 75-80 MPH on TX highways and mostly 70 on CO mountain roads. It was consistently windy in TX and snowing in CO. My MPG was close to 18 in Colorado and 17.5 on highways (2.7L 4-door sasq, hard top, bare roof).

Like others already mentioned - when doing over 80 MPH, even mild headwind will significantly affect MPG and handling - so I trying to not exceed 80 regardless of the limit (except to pass). Bronco has aerodynamic characteristics of semi-deployed parachute made of steel.

 

[ProdigyJKU]

Colder would mean more dense air and better mileage, but to your point, it could be winter gas. Didn't think about that.

Dense air means more fuel required to maintain the proper air/fuel ratio. Dense air also means more aerodynamic resistance on the highway.

Hot/thin air is the best for fuel economy. Cool dense air is the best for maximum power, which leads to poor economy.

 

[JohnnyBronco]

Colder would mean more dense air and better mileage, but to your point, it could be winter gas. Didn't think about that.

The higher the corn content the lower the mpg. If you ran E85 you might be lucky to get 10-12.

Maybe not exact but there is science that adding alcohol lowers mpg. Think about how far an F1 or Indy car running pure alky goes before fillup

Strange thing I found in Nebraska, home of ethanol, stations with 0 ethanol blends. Go figure

 

[PSUTE]

I notice a difference between brand name fuels and convenience store gas. I usually run Exxon or Sunoco...

 

[cricex]

I happen to drove from Austin to Breckenridge and back two weeks ago.

I normally cruise 5 miles over speed limit, basically a combination of 75-80 MPH on TX highways and mostly 70 on CO mountain roads. It was consistently windy in TX and snowing in CO. My MPG was close to 18 in Colorado and 17.5 on highways (2.7L 4-door sasq, hard top, bare roof).

Like others already mentioned - when doing over 80 MPH, even mild headwind will significantly affect MPG and handling - so I trying to not exceed 80 regardless of the limit (except to pass). Bronco has aerodynamic characteristics of semi-deployed parachute made of steel.

Did exactly what you did, same mph and everything, and got 13mpg.

I do have a softop which would impact drag, but I guess the point is I normally get 18 highway and all the sudden I lost 30%.

Filled up with ethanol free 92 or 93 octane @ QT before I left (i normally fill up with ethanol free fuel)

 

[Mrpenn46]

The higher the corn content the lower the mpg. If you ran E85 you might be lucky to get 10-12.

Maybe not exact but there is science that adding alcohol lowers mpg. Think about how far an F1 or Indy car running pure alky goes before fillup

Strange thing I found in Nebraska, home of ethanol, stations with 0 ethanol blends. Go figure

The science is there is less energy in ethanol than gasoline so diluting the gas means you need to burn more to release the same energy.

The trade off is the carbon is "neutral" because the next crop of corn absorbs the carbon to grow, that's the theory at least.

 

[BigMeatsBronco]

You're looking at it the wrong way. Cold, dense air definitely helps make more power... But you're not wanting more power cruising down the highway at the same speeds you were going in the autumn. However, colder denser air creates higher resistance to passing thru it, so in all likelihood, you were needing more power...

Absolutely correct, pilots learn this ...also the dense cold air requires MORE fuel to burn at 14.7 ratio...while this might make more power in theory, and require a tad less pedal, it has to do with the engines volumeric efficiency. The engines capacity is not as variable as the oxygen density available in our atmosphere.

 

[BigMeatsBronco]

The higher the corn content the lower the mpg. If you ran E85 you might be lucky to get 10-12.

Maybe not exact but there is science that adding alcohol lowers mpg. Think about how far an F1 or Indy car running pure alky goes before fillup

Strange thing I found in Nebraska, home of ethanol, stations with 0 ethanol blends. Go figure

Absolutely correct, and the new Bronco has a fuel system that CAN deliver 50% more fuel than needed partially for this exact reason. E-85 is drastically cheaper than 93 octane though (at least where I'm at) over $1.55 cheaper per gallon, so that needs to be taken into consideration.

Funny thing is when I run 50/50 E-85, a full tank only gets me 225miles. But those miles are RADICAL with the extra power available from high octane and tuner.

 

[Ksjrb03]

Im getting about 2mpg less lately than before. Was averaging about 15.5 and the last month has been high 13s. More highway than city driving, and I dont drive slow here in Texas. I chalked it up to "winter gas" but honestly Im not sure if that is even a thing around here. I've been driving diesel super duties for 20 years, it amazes me my big lifted 6.7 gets way better mileage than the little Bronco, not that I really care.

I have been putting gas at Walmart lately due to convenience, maybe I need to go back to the Exxon gas I was using before.

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