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Posted: 6/30/2015 2:19:41 PM EDT
This is the second year I've noticed this and wonder if any car experts have an opinion.

I have a 2012 Forester. I bought it in Georgetown, TX.

In Texas, I get about 20-22mpg on the highway on regular 87 octane gas.

When I've gone to Colorado and Utah on vacation, I'm putting in 85 or 86 octane regular and at higher altitudes and getting 24 or 25 mpg.

I would think the lower octane gas and the less dense air would lower mileage, not raise it. I don't think it's driving habits, because I mostly use cruise control on the highway at the speed limit.

Any ideas what might be happening?

Link Posted: 6/30/2015 2:25:52 PM EDT
More ethanol in Texas gas?

Also, all those bug splats create drag
Link Posted: 6/30/2015 2:31:05 PM EDT
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Quoted:
More ethanol in Texas gas?

Also, all those bug splats create drag
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It is my absolute belief that the only "up to" promise ever really fulfilled by corporate America is "may contain up to 10% ethanol"

These are all lies:

last up to 6 weeks
Up to $100 off
Up to 100Mb/s
lose up to 5lbs a week

But not the promise of up to 10% ethanol. I bet it is exactly 10.00% every time.



Link Posted: 6/30/2015 2:36:54 PM EDT
I noticed my fuel economy improved when I left Florida for the Rockies last year. I guess the rest of the country gets good gas.
Link Posted: 6/30/2015 2:37:36 PM EDT
Hot air is less dense?
Link Posted: 6/30/2015 2:57:47 PM EDT
Maybe more air needs more fuel to keep the mixture right, or AC running harder.
Hot gas isn't as dense as cold gas.
Link Posted: 6/30/2015 4:07:29 PM EDT
At higher altitudes the air is less dense. Therefore the computer adjusts the air/fuel ratio to compensate. Less air = less fuel. This also means less power from the engine.
Link Posted: 6/30/2015 4:12:40 PM EDT
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Quoted:
At higher altitudes the air is less dense. Therefore the computer adjusts the air/fuel ratio to compensate. Less air = less fuel. This also means less power from the engine.
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But also less drag.  So that helps balance it out a bit.
Link Posted: 6/30/2015 4:17:07 PM EDT
What is physics for 200 alex
Link Posted: 6/30/2015 4:31:10 PM EDT
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What is physics for 200 alex
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This is when calculus comes in, optimization and integration.

Like how much fuel does a rocket need.
Link Posted: 6/30/2015 5:14:24 PM EDT

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Quoted:


Maybe more air needs more fuel to keep the mixture right, or AC running harder.

Hot gas isn't as dense as cold gas.
View Quote
That would be my first guess.



 
Link Posted: 6/30/2015 5:20:49 PM EDT
Ethanol crap. Ive seen big differences in my mileage when I'd use pure gas vs the corn fed crap.
Link Posted: 6/30/2015 7:12:42 PM EDT
Quoted:
This is the second year I've noticed this and wonder if any car experts have an opinion.

I have a 2012 Forester. I bought it in Georgetown, TX.

In Texas, I get about 20-22mpg on the highway on regular 87 octane gas.

When I've gone to Colorado and Utah on vacation, I'm putting in 85 or 86 octane regular and at higher altitudes and getting 24 or 25 mpg.

I would think the lower octane gas and the less dense air would lower mileage, not raise it. I don't think it's driving habits, because I mostly use cruise control on the highway at the speed limit.

Any ideas what might be happening?

View Quote


What brands of gas are you using?
Link Posted: 7/1/2015 1:36:19 PM EDT
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Quoted:

What brands of gas are you using?
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I try to stick with name brands, Shell, Chevron, Texaco, etc... I don't ever get Valero, Race Track or any of that stuff.
Link Posted: 7/1/2015 1:51:11 PM EDT
Because physics, if it was always super hot and humid I'm sure you'd see about the same provided you didn't run the AC.  If it's the turbo version you're retaining a lot of efficiency at higher altitudes and combined with non ethanol gas you're getting more energy out of the fuel.  


Hot and humid not running the AC I can get around 37mpg highway with my Lexus.  Drops significantly with lower humidity and temps because you're pushing a lot of air at the highway speeds here.
Link Posted: 7/1/2015 1:57:49 PM EDT
Everything's bigger in Texas, including gravity.
Link Posted: 7/1/2015 2:21:10 PM EDT
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Quoted:
Everything's bigger in Texas, including gravity.
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Both my truck and wiener grew 8 another inches, he's not kidding.
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