[boilerhoops10]

Have a question:

Is there a pretictable relationship between gas mileage and elevation? I am an engineer (of the semiconductor kind), so I'm a bit embarassed to ask such a question, but we live and do all our driving at an elevation of ~5000 ft. After about 2000 miles, we are averaging about 16 mpg. Granted, most of our driving is of the city variety, but I'm still a little disappointed with the overall gas mileage. I have been wondering if our elevation might make a difference. Thanks in advance for the inputs.

 

[tim.s]

Mileage will decrease with altitude as the air thins out and the fuel-air mixture gets too heavy. But smog and air pollution will increase as you go lower in altitude so I'm not sure what the net affect would be.

You will probably see lower average mileage if you do all your driving in a warmer environment. My mileage will drop by as much as 2 mpg in the summer (90 to 100°C) verses winter (30 to 50°C)

Here's a link describing horsepower verses temp, horsepower verse altitude, etc... and how they effect mileage.

Horsepower is typically measured at sea level as explained in this link simply because it is higher there.

 

[colorider]

Have a question:

Is there a pretictable relationship between gas mileage and elevation? I am an engineer (of the semiconductor kind), so I'm a bit embarassed to ask such a question, but we live and do all our driving at an elevation of ~5000 ft. After about 2000 miles, we are averaging about 16 mpg. Granted, most of our driving is of the city variety, but I'm still a little disappointed with the overall gas mileage. I have been wondering if our elevation might make a difference. Thanks in advance for the inputs.

I'm sure there is some - mainly because the air is thinner and the engine has to work a little harder. I currently live and work right at 5,000 ft - about the same as you, and my mileage is averaging about 21-22 with 70/30 HWY/CITY driving. In my previous life, I lived at 8700 feet and commuted to an elevation of about 6,000 feet. I was driving Subaru's and VW's at the time and my mileage was always pretty consistent with the EPA ratings of the vehicle.

YMMV

rod

 

[colorider]

Oxygenated

One more thing I forgot to mention - you are probably required to use oxygenated fuel there, just as we have to here. When we are in the "program cycle", my mileage drops about 10% on all my vehicles.

rod

 

[N_Jay]

Interesting question

Is there a pretictable relationship between gas mileage and elevation? .

All my intuition says yes, but:

Being as the engine control system is a closed loop system, and has some amount of adaptive learning, I can not think of a good reason why it should be worse.

Peak available HP will be lower, but how often do you use that?
It will take a greater throttle opening to get he same HP but that should actually increase efficiancy as it decreases "pumping losses".

 

[01r1]

My experience is yes and no to this MPG/elevation relationship. True, less power due to thinner air, but thinner air equals less wind resistance. I have seen no difference in MPG when cruising on the highway at sea level or 8000ft. I have seen a decrease in MPG when driving in stop/go city traffic at high altitude. I guess it still takes the same amount of HP to get the car moving, regardless of elevation, but at high altitude you just have less HP to work with.