Altitude effects upon gas mileage

Same as a lady claimed last week, I get better mileage at 8,000 feet than down here in Florida. Ten trips back and forth from Florida to Colorado, so pretty good record.

Ford Ranger, V-6.

Mileage goes from about 24 mpg to 27 or 28 mpg. Power is less, but not a biggie.

I don’t see this on our Subaru Outback - maybe 5 or 6 trips.

Anybody else notice this?

Gums sends…

Our best gas mileage ever in a Honda Element happened driving around the Enchanted Circle area of Taos NM. 28 mpg or so.
Normal gas mileage near sea level is around 22-24 mpg.

There’s a reason why airlines cruise at around 30,000 ft.

It’s perfectly logical. There’s less oxygen per volume at altitude, so if you continue driving the same way you do at sea level, accepting the lesser power, than you’ll use less gas.

On a motorcycle, the change in aerodynamic drag is very noticeable…

At sea level, a cubic yard of air weighs about 2 pounds. At highway speeds, the lions share of the energy the engine has to deliver to whe wheels is the energy needed to push all of that air out of the car’s way.
Air that only weighs 1.75 pounds per cubic yard obviously needs less energy to push out of the way.
Also, the less dense air effectively gives your engine less displacement.


I kinda figured that the air density had a lot to do with, although in my old '64 Pontiac Tempest I got less power AND less mileage up high. Basic carb motor. Same for my '69 Cougar with that 351 cu-inch motor.

Guess these new injector computers do a good job getting the best stochiometric ( sp?) ratio, huh?

There could be a difference due to air density at interstate cruising simply due to drag. In my case it was crawling up from the Springs to 8,000 ft and then back for more lumber, nails and grub.

Driving habits may be in play, as I drive the same way everywhere. I don’t try to get to 60 mph in 10 seconds, so I laugh when the jackrabbit and I pull up on the next traffic signal and sit together. Bet I get 10 - 20% better mileage if I drove HIS car!

What has surprised me is the newer Subaru shows only a very slight increase in mileage compared to the Ranger. A 10% increase seems pretty good in my view.

And BTW, I am very used to cruising up in the stratosphere. About 4,000 hours in fighters using various turbine motors. The range went way up when high due to true airspeed, lower air density, and the way those things worked, heh heh.

Thanks for all the comments, as I was afraid I was the only one besides the lady that called Click and Clack.

Gums sends…

And there’s a reason why planes with internal combustion engines don’t.

Of course when you say “weighs” you mean “has a mass of” right?

Of course when you say “weighs” you mean “has a mass of” right?


Jets engines are internal combustion engines.

B-17’s and other WWII bombers flew that high, to be above the range of flak guns if nothing else.

I go from OK to CO quite frequently and the fuel mileage on my prior Lincoln and my current one both jumped up by about 1.5-2 MPG or so. The altitude here is about 1100 feet and most of my time there is in the mountains.
One would think that pulling grades with a loaded car would drag the mileage down but this is not the case.

With a prior Mercury (OBD I system) and a prior Subaru the fuel mileage dived a little at altitude on those 2 particular cars.

Piston engine aircraft do cruise at high altitude. That’s the main reason for super or turbocharging. Look at the WWII P-38 Lightning as an example. I think the service ceiling on that one was near 40,000 feet.

We have been traveling west to the mountains on camping trips and this question has bothered me for years. The mpg in older vehicles with carburetors would decline, but with newer engines we noticed an increase in mileage. This happened with two different Astro vans and our current Honda. We were told that it was the mountain blend gas that we were buying, that was making the difference. We would average better mpg?s in the mountains than we could get at lower altitudes on flat land, with a tail wind. The air density might be part of the answer, but most of our time was either spent at slow speeds pulling a camper uphill, where wind resistance would have the least effect or coasting downhill at higher speeds with an engine working as a brake, when the wind resistance would be highest. My father-in-law also noticed the same thing with his Crown Vic.

There are a couple of things at work on an older carbureted vehicle when it comes to altitude.
An engine has a tendency to run richer at higher altitudes and with some exceptions, most carburetors are designed to operate at lower altitudes. What may be fine stoichiometric-wise at lower altitude is often too much at high elevation and the carburetor will meter more fuel than needed.

Ignition timing is generally controlled by engine vacuum and this will vary at altitude also. The engine timing will often run a bit more retarded than normal and retarded timing is essentially richening up the mixture.
This often means that the timing should be advanced a bit while in the mountains.

When traveling to CO back when in an older, distributor equipped vehicle I used to make a series of marks around the distributor base at 2 degree increments and take along a distributor wrench. At altitude I’d just bump the timing up accordingly and back it off when reaching lower altitude.

At one time some car makers offered electronically controlled carburetors which used one version for lower altitude and another slightly modified one for cars being sold in mountain states like CO.

I understand that one of the biggest problems with high altitude flying was keeping the engines cool. The thin air at high altitude is not as effective a coolant as dense low altitude air is.
This is also noticeable when one is on the ski slopes. It’s 25 or so degrees out there but it feels more like 35 on your skin.


Ya got it, OK. We did the same thing back with my 64 Pontiac.

Advanced the timing about 2 degrees for every 3,000 ft until the engine pinged, then backed off.

There was also a set of carb jets you could install to lean out the mixture a bit.

IMHO, Click and Clack have to confirm that lady’s observation. Too many responses here confirm the urban legend. Of course, some vehicle computers may not correct for the air density like others do…

Gums sends…