Altitude affects on mileage

We have a a higher elevation area to drive to here. When we drive up there the mileage increases dramatically. I have tried it 3 times to confirm it is not my imagination. Any ideas of how to make our 2007 Durango think it is at a higher elevation when it is not?

In the olden days we used to advance timing for driving in the high altitudes, I think you are better off not worrying about it.

I don’t think you can fool your Durango’s computer. What I think is happening is that the computer is advancing the timing. Further, the gasoline at higher altitudes is usually a lower octane. If you are using the higher octane from lower altitudes, the computer is really advancing the timing. If the computer set the timing this high at lower altitudes, you would have detonation–a very damaging spark knock.

Also you’re pushing that truck through thinner air, which offers less aerodynamic resistance. That’s why airliners fly at 30,000’ or more, where air is only 1/4 as thick.

Note that you only save gas if your vehicle is smart enough to adjust fuel metering for the thinner air: a car with a carb/“dumb” EFI would run rich, and FE would suffer as a result.

There’s also less wind resistance at higher altitudes, and the Durango has a lot of wind resistance to lose.
That’s why jet planes need to climb to 30,000+ feet in order to cruise efficiently at 500mph

I’m in agreement about the thinner air. After numerous trips to CO my cars have all picked up around 1.5-2 MPG at altitude even when running a lower octane gasoline.

The question in my way of thining isn’t why the mpg is considerably better at higher altitudes, but why is it considerably worse at lower altitudes? It’s true that thinner air means less wind resistance. I’ve taken a golf vacation at 6000 feet, and the ball definitely goes further at that altitude than here at sea level. I have to adjust which club I use for the same distance. But I think you are saying the mpg numbers are quite a bit different. 1 or 2 mpg would be about the most I’d expect from wind resistance, and that would only show up in high speed driving. I’m thinking there may be something wrong with one of your engine sensors. For best performance and mpg, the fuel/air mixture and timing need to vary according to altitude. On older cars, you had to decide if you wanted to drive at low or high altitudes, then they’d fit you with the appropriate altitude kit. Newer vehicles usually have a sensor which measures the altitude, and adjusts the engine parameters accordingly. The “MAP” sensor can be used, or a separate sensor. Either way, it should be possible for your mechanic to pull the sensor and bench test it. Your engine computer may think the car is being driven at a different altitude than it actually is.

In modern cars the O2 sensor is the final judge of fuel/air ratio, compensating for altitude or anything else, within limits.

How about this: at higher altitude the engine needs a wider throttle opening to get in the amount of air needed to give the power required. Wider throttle = less pumping losses = somewhat better efficiency.