Driving at elevation

I have a two part question about driving at higher elevations. One, despite having diminished hp, does a car experience better or worse gas mileage? If the air is less dense, wouldn’t there be less air resistance? Two, does a cars ability to cool diminish?

How much elevation are you talking about?  In all but extreme cases any differences will be very small indeed.  You would be lucky to be able to measure it.

The car’s mass air sensor will probably adjust the amount of fuel at the injector. Or perhaps just inject the same and you will have less power because there is less air in the charge. I think the answer is the later.

I have lived in Colorado for 34 years and drive back to Nebraska and always notice the power differential so the engine can mostly likely only take in so much volume per cycle and if not having more air pushed in (like a super charger) develops less power.

I have never noticed a mileage differential and have driven the same truck for 18 years and have driven it 370k miles (yes that is true and it is a toyota that has 379k miles and i bought it used with 7k miles).

Cooling. Their air is cooler at altitude. Their is less pressure (ambient air pressure), but the cooling system is a closed system. Good question. Fuel has a problem in that it vaporizes more quickly at a higher altitude and can cause vapor lock. I had a ford pickup that had to have fuel pump installed to pressurize the fuel to keep it from vapor locking (it was carbureted and had a mechanical fuel pump).

There’s no set answer. It depends. My car’s mileage actually improves at altitude (1 to 1.5 MPG) but power is diminished. The rule of thumb is a 3% power loss for each 1000 feet of altitude.

By ability to cool I assume you mean the engine temperature. I go to Colorado quite a bit and when pulling steep grades runs the engine temperature up. Engines temps are only slightly elevated on the high altitude flats and of course on downhill coasting the temps drop considerably.

The smaller and weaker the engine the more prone it may be to engine temperature spikes. My current LIncoln doesn’t rise much but a few other cars I’ve driven to CO (older Subaru, SAAB, etc) would suffer temperature rises that made it a bit uncomfortable for me and caused me to really keep an eye on the temp gauge.

How the mileage is affected will vary by vehicle. Yes, there’s less air resistance, but also reduced oxygen, which is necessary to create power.

There are fewer air molecules to remove heat energy…but there’s also reduced oxygen and density, resulting in less intense explosions in the cylinders.

The amount of mass necessary to move will remain constant, the energy to accelerate it constant, but there’ll be reduced resistance to its inertia once it gets moving due to the reduced air density. The same amount of fuel will be necessary to accelerate, but less to maintain speed. How much less depends on if you’re driving a Prius with low rolling resistanmce tires or a Navigator…a giant rolling brick with huge rolling resistance.

The “less intense explosions” are affected by this too. The same amount of energy will be necessary to drag the vehicle up a mountain, but the speeds may be slower because the ability of the engine to totally compensate for the lower oxygen level may be compromised. It all depends on the design.

How everything balances out against one another is highly dependent on the overall vehicle design.

What are you driving “at elevation” ?

On carburated vehicles you can clearly see a change in function as the carbs are not self adjusting for air/fuel ratio.
My 80 Bronco 351m would over heat when driven at lower altitudes.
Adjusted for home 6500 ft, it would over heat some in Albuquerque 4950 ft, and downright boil over down in Ohio or California.
Not being adjusted at lower altitude lets in relatively MORE air per same fuel and results in a lean burn which burns hotter.
( My Cessna 172 had an adjustment for air/fuel mix and I’d watch the exhuast temp guage and adjust as needed. ) I learned which screw to turn to bring in less iar and bring down the temp.

I 'm a fan too of the vehicle dependent response. Diesels which I have driven which need copious amounts of air may be more effected by altitude. But, air density varies not only with altitude but temperature as well where generally higher altitudes are cooler. That, along with “climbing” mileage losses leaves me confused on this issue and a thank goodness we now have a computer to deal with all of the variables. I’m at a stage in life where it’s more important just getting over the mountain in one piece then worry about the mileage difference doing it.

The only major altitude related difference I recall noticing when driving over passes in Colorado was seeing all of the Buicks and Dodge/Chrysler/Plymouth minivans overheated on the uphill grades.

As for performance, climbing a steep hill at any altitude causes you to use more gas, and really, driving a car as if you were on the Pikes Peak Hill Climb race is a recipe for disaster in most mountainous areas. Never noticed an appreciable drop in gas mileage on my 1985 2.5L 4 speed S-10 or any other areas of note - and I used to watch my gauges and gas mileage like a hawk because it was an old truck.

<font color="blue"jstewar2 — "The car's mass air sensor will probably adjust the amount of fuel at the injector. Or perhaps just inject the same and you will have less power because there is less air in the charge. I think the answer is the latter."
Think again.

My wife’s Honda Element got the best gas mileage ever during a week of driving around the mountains of Taos NM, over 30 mpg on that tank of gas. A lot of the credit might go to that area’s low speed limits and to the fact that I used the cruise control a lot just to make sure I obeyed those speed limits. Also, the climbs and coasts kind of forced the old pulse and glide gas mileage technique on the driver so it’s hard to tell if the elevation alone caused that gas mileage. I believe it certainly contributed.
Anyway, it demonstrates that you don’t HAVE to get crappy gas mileage just because you are driving in the mountains.

In high elevation driving, the thinner air causes less air resistance plus the thinner air effectively reduces the displacement of your engine. High elevation air also cools less effectively, it’s one reason why 25 degrees doesn’t feel so bad when you are skiing at 10,000 ft above MSL but it chills you to the bone when you experience it at seal level.