mpg at altitude?

[Rambler29]

I live at 6000 ft and do not get the kind of mpg that many on this forum report. Is it possible that mpg at sea level is better? I get around 37 mpg all around in rural Conservative driving, 40 at 65 on cruise control is good for me. I had a 10 jsw (9900 miles) and now an 11 jsw with 2400 miles so far showing very similar mpg.
PS...I would love this car if it only got 25 mpg!

 

[axnels2]

I live in Denver and my mileage is a little worse then yours but I drive mostly in the city during the week. I did a lot of readup on this and concluded that altitude does not impact these engines much because of turbo but what does have a big impact is rolling hills, stop and go traffic, wind and big mountain passes.

 

[UFO]

Mileage improves with altitude. The air is less dense, and has less drag on the car. I live in Denver, and my vehicles get better highway mileage through the mountains than across the plains.

 

[MayorDJQ]

I would say that the thinner air at elevation isn't thin enough to make a difference. I saw my best MPGs on my PDX-TDIFest10 roadtrip travelling in the Plains. I was seeing 43-46mpg for the bulk of OH, IN, IL, IA, and NE. Climbing up into CO I took a hit to 39-40. Running across the plain of WY I went back into the low 40s. Running through the desert from SLC to Reno I was getting 45mpg with A/C at 72mph. The 40 mile downhill grade from Tahoe toward Sacramento was fun and the MPGs jumped into the high 50s, but came back down once I was out of the mountains.

 

[RomanL]

ill reprot back when i do my drive from LA to Denver in december.

 

[Victor-Whiskey]

I am a pilot with over 2000 hours; I'll chime in...
At high altitudes drag decreases faster than power drop off. So, less power is needed to maintain a given speed. At 9000 ASL, I can do the same speed in a Bonanza with 60% power setting that it takes at 80% at 2000 ASL. (given no other wind conditions)
That figure is with level flight. As we all know, high altitude driving is never level for very long. Ascents are fuel killers in cars and planes. I'd place my mpg bets on flat terrain at any altitude. And before anyone says it; no, coasting descents won't make up for the power/fuel needed for ascents. If you could drive across the Rockies on a level road at 8000 ft; then yes, your mpg would be awesome.

 

[RomanL]

thats very interesting.
i know that there arent really any flat stop at very high altitudes.
but techincally speaking same driving at sea level vs driving on flats at some parts of UT which are considered high desert since they're sitting at like 5 to 6K ft above sea level, and are flat for long distance, so technically people there should get better milage? very cool

 

[F100boy]

I am getting 42 MPG running 72mph on the two lanes. 37-38MPG running 83mph on the interstate. I have just passed the 33K mark on the odo. I live in Wyoming, at 6800 feet. Car runs well, Best MPG i have ever ran has been 54.9 MPG on a perfectly flat two lane, i was only running 50 miles an hour.

 

[StewartinND]

THe tdi should make its sea level hp up to what ever the critical altitude of the turbo is. I know from flying turbo'd airplanes that tends to be in the mid teens however the turbo diesel aircraft engines its in the 8 to 10k feet range.

That being said when your up high in a tdi you get the best of both. Lower drag and normal power and ever so slightly less gravity that you should see slightly better milage and I have seen a few extra mpg's while at higher altitudes.

 

[jluke78]

Another Denver guy here, I saw 52.9 MPG going up into Silverthorne 2 weeks ago. About 9000 ASL.

 

[Biffster]

You can find the best explanation here. It has to do with gas-powered engines, but the principles should be the same.

In summation, you can get better mileage, but with less power.

 

[SummiTDI]

I'm sorry but I have to call B@@@@it on 52 mpg

I live in Breck and drive up and down 70 a decint amount. Never have I even seen close nor has anyone ever seen those numbers. Time to pull up my wadders

 

[StewartinND]

You can find the best explanation here. It has to do with gas-powered engines, but the principles should be the same.

In summation, you can get better mileage, but with less power.

You have to remember the tdi is turbocharged so the air entering the engine is above atomospheric pressure to begin with. As you climb in altititude the wastegate will close to maintain that pressure till the wastegate is fully closed at full throttle (critical altitude) and at that point the engine will begin to loose power with increasing altitude. We have the same amount of power availabe but now have to use less of it due to the reduction in drag = even better milage

 

[ruking]

I live at 6000 ft and do not get the kind of mpg that many on this forum report. Is it possible that mpg at sea level is better? I get around 37 mpg all around in rural Conservative driving, 40 at 65 on cruise control is good for me. I had a 10 jsw (9900 miles) and now an 11 jsw with 2400 miles so far showing very similar mpg.
PS...I would love this car if it only got 25 mpg!

If you take a look at the monthly mpg competition, you will see there are a lot of folks who get 37 mpg and presumably @ more toward sea levels.

Since your 2011 JSW is rather new, I would actually focus on break in procedures and let the numbers fall where they may. It really starts with an understanding of your 2011 JSW's VW owners manual technical page.

You do not say what transmission you have, but I would swag a DSG 6 speed. While EPA figures put it app the same as the 6 speed manual, the fact of the matter is the 6 speed manual is capable in the real world of having a greater range of mpg.

My 09 Jetta Sedan DSG has had a range of 40-47 mpg or range of 7 mpg. When operated @ over 5,000 feet, it pretty much gets the norm 42 to 44 mpg. Now I do not know the range of a 6 speed manual on the later model TDI's (09,10,11).

As a comparison, my 03 TDI 5 speed has a range of 44 to 62 mpg or a range of 18 mpg.

All the best !!

 

[jluke78]

I live in Breck and drive up and down 70 a decint amount. Never have I even seen close nor has anyone ever seen those numbers. Time to pull up my wadders

Well, you also are carrying around 400 more pounds. My worst tank so far has been 38.3 mpg city. You can call BS, but I have no reason to lie about the mileage I saw.

 

[bruce846]

OK, you are all cleared to land on runway 15, please call final and have a good day.

 

[mattymx]

You can find the best explanation here. It has to do with gas-powered engines, but the principles should be the same.

In summation, you can get better mileage, but with less power.

The principals will not be the same when gas vs diesel is concerned... Ever... In a gas engine you must keep the air/fuel ratio as close to 14.5/1 as possible. That is called the stoichiometric ratio. If you run a gas engine leaner than that under heavy loads, it will damage the engine.

A diesel engine will ingest all the air it is given without worry of a lean condition. That is why in 1994 the EPA mandated that all on road diesel engines be equipped with a turbo. Diesels love to be lean and high altitude does not help that at all.


Now back on track... With the lower oxygen value of the air at altitude vs sea level, you will obviously have a slightly richer condition. In a diesel, that means slightly higher EGT's and slightly lower MPG... Not a ton lower, but a little. I live at 7000ft.

 

[dwpc]

I don't think lower drag from thinner air has a thing to do with it unless your cruising at 180 knots or more. At highway speeds, perhaps a minor fraction of a mpg, no more. Higher elevations usually mean more grades and uneven throttle use. I suspect that's the difference. Anecdotally, I frequently drive from So CA to N AZ and my mileage is typically about 2 mpg higher at 4000+ that on the desert at 1200 ft. I chalk it up to 15-20 degree cooler, denser air at elevation.

 

[falconguy]

But air density goes down as altitude goes up?

Temp might explain it, also do you turn off the ac cause that mpg hit seems close.

I'm thinking I'm ocd about all my cars but my hats off to those who pinpoint things like this. No sarcasm either, good observations.

 

[dwpc]

But air density goes down as altitude goes up?

Temp might explain it, also do you turn off the ac cause that mpg hit seems close.

I'm thinking I'm ocd about all my cars but my hats off to those who pinpoint things like this. No sarcasm either, good observations.

I said that the suggestion that higher mpg from decreased drag (from thinner air) is probably a non-starter at routine driving speeds. Density due to temperature, though, is a significant consideration. Someone into Boyle's Law can figure it out.

My 2 mpg delta was without AC. Last week it was in the 50s driving the higher elevations driving I-17 north of Phoenix; in the low 70s on I-10 on the desert.