Gas mileage at altitude - explain like I'm 6

[SpokaneCY]

When I Ask Jeeves, he says MPG at altitude goes UP due to manifold air pressure (or Johnson rods rotated) or something and that lower octane fuel - in this case 85 - is a better alternative. I recently (in the last 5 days) moved to CoSprings from Spokane. 2,500' vs. 6,500' and my milage has gone down.

Can a car guy/gal, or engineer with communication skills explain it as if I'm 6?

 

[mywayorcyway]

I'm looking forward to this thread.

 

[CyCrazy]

Wait Ask Jeeves is still a thing? Otherwise I don't care.

 

[Cyched]

Wait Ask Jeeves is still a thing? Otherwise I don't care.

RIP

 

[Acylum]

I wouldn’t expect a huge difference either way given a 4000’ difference in a modern, FI vehicle.

 

[CycloneDaddy]

Are you only driving uphill?

 

[Gunnerclone]

The air is less dense at altitude and therefore assists the aerodynamics of your vehicle, making it more fuel efficient.

Signed,

someone that knows nothing about the topic and just made that **** up

 

[Cyched]

Have you tried turning the car off then turning it back on?

 

[keepngoal]

Clearly, at this new higher altitude, you’re driving uphill both ways.
/thread

 

[DarkStar]

As altitude increases, air gets thinner. At higher altitudes, the same volume of thinner air contains less oxygen to combust with the fuel. Combustion efficiency goes down.

Generally speaking, an engine loses three percent of its rated power for every 1,000 feet of altitude gained.

Edit: I should add that a computer chip in your car tries to control the fuel to air ratio for your driving conditions. It will take it some time to figure out your typical air density has changed and will stop sending as much gas for every cycle. You'll still have less power but you won't be wasting as much gas to get that lesser power output. Same reason why lower octane gas is ok.

 

[gocy444]

I’m still stuck on the Ask Jeeves part...

 

[MeowingCows]

At sea level: car go BRRRRRR, use gas

Way above sea level: car only go brrrrrr, but use less gas. Net positive MPG

 

[aauummm]

As altitude increases, air gets thinner. At higher altitudes, the same volume of thinner air contains less oxygen to combust with the fuel. Combustion efficiency goes down.

Generally speaking, an engine loses three percent of its rated power for every 1,000 feet of altitude gained.

Agree.

Also: "Turbocharging at elevation is an efficient way to minimize horsepower loss due to elevation and lower air density. At high elevations turbochargers compress more air into the engine cylinders making up for the lower air density allowing the engine to produce power as if it was at sea level."

So the OP needs to get a turbocharged car to improve power and gas mileage. However as someone noted above, 4,000 ft elevation rise isn't much and isn't enough to worry about.

 

[SpokaneCY]

Are you only driving uphill?

Both ways in the snow! But I'd say same elevation gain range in both places... 1,500-3,000 in Spokane and 5,000-6,500 here.

 

[SpokaneCY]

As altitude increases, air gets thinner. At higher altitudes, the same volume of thinner air contains less oxygen to combust with the fuel. Combustion efficiency goes down.

Generally speaking, an engine loses three percent of its rated power for every 1,000 feet of altitude gained.

Edit: I should add that a computer chip in your car tries to control the fuel to air ratio for your driving conditions. It will take it some time to figure out your typical air density has changed and will stop sending as much gas for every cycle. You'll still have less power but you won't be wasting as much gas to get that lesser power output. Same reason why lower octane gas is ok.

I HAVE noticed less oomph from my CRV sex-mobile...

And you confirmed what Jeeves said but you DID provide way more detail on the why... Greatly appreciated!

 

[SpokaneCY]

At sea level: car go BRRRRRR, use gas

Way above sea level: car only go brrrrrr, but use less gas. Net positive MPG

As if I were 6... And I kinda get it - especially with the vroom vroom enhancements!

 

[SpokaneCY]

Agree. "Turbocharging at elevation is an efficient way to minimize horsepower loss due to elevation and lower air density. At high elevations turbochargers compress more air into the engine cylinders making up for the lower air density allowing the engine to produce power as if it was at sea level."

So the OP needs to get a turbocharged car to improve power and gas mileage. However as someone noted above, 4,000 ft elevation rise isn't much and isn't enough to worry about.

Kinda sounding like the car just has to learn the new driving environment.

 

[nfrine]

So the OP needs to get a turbocharged car to improve power and gas mileage.

A turbocharged Jeep Wrangler.

 

[BoxsterCy]

If you ain't smoking weed in CO your mileage is likely to suffer. Plus you're driving a Jeep.

 

[BoxsterCy]

BTW, my gallons per week rate the last four months is out ******* standing.

And, I'm a flatlander with no weed, just lots and lots of wine.