High Elevation Fuel Economy

[Slow Riviera]

Does anybody here know why my trucks computer would show that I got approx. 2 mpg better fuel economy while driving around south central Colorado than I do in Oklahoma. lower air density, gravity, humidity, less atmospheric press. on my tires? In Colorado I was driving between 6000-12,000' elev. The truck did great by the way.

 

[B.G. Smith]

I think the computer comes up with it's numbers by looking at the MPH input to the computer and the throttle position. Since you are going downslope about half of the time, it gets carried away with the input from the throttle position/MPH while going downhill. Just my theory. bg

 

[JFlagg]

Hand figured I got better mileage in CO than MO on one hunting trip. It was in the single digits and around 7-8000' too, I think it was just a fluke...

 

[Sean Flanagan]

I live in COlorado and have definitely noticed my mileage is a bit better here where I usually am between 5000 and 10000 feet. Cruzing on the highway in Colorado, I am happily get about 19+. Each year I make some road trips to Oregon and again to south Texas. My economy gradually drops to about 17 by the time I get to sea level. My old '98 did the same thing too. I figure it is the lower air density making less wind drag...

 

[raksasa]

Same reason a golf ball flies a greater distance in Colorado vs, Florida... less drag from the lower partial pressure of the atmosphere. It's also why you become "winded" sooner when you exercise at altitude - less atmospheric pressure in your lungs to force the oxygen into your bloodstream. Even my crummy Dakota achieved decent mileage in Colorado and Utah!

 

[petersonj]

Lower friction from lower air density at high altitude reduces drag on you truck. I lived in Leadville, Colorado for 12 years (elevation is 10,200 ft). I installed a 1988 Cummins 4BTA in a '91 F-150, 4wd, short box, 5 spd manual, while I lived there. Prior to that, the engine was in a 1984 Ford van, E 150.



I kept a log of all fuel that went into the truck for 150,000 miles. I made many round trips to Redding, California, and Portand, Oregon during those years. Fuel mileage was always about 2 mpg higher when I was at home in Colorado.



I also noticed that when I traveled down long 7% downgrades (starting at 11,000 ft) in Colorado, I needed to apply brakes frequently. In Oregon and northern California, those 7% downgrades started at around 4000 ft, and very little, or no braking was required. So, yes, air density plays a significant role in fuel economy.

 

[DJW]

Strange, I noticed some years ago while driving a Ford gas 6 cylinder in the high country of Colorado, seems the truck went further between fillups although I did not check mileage, also seemed to have more go, granted I was traveling light and just a seat of the pants feeling. My thoughts at the time was it was not possible owing to less air, thus oxygen, where as more air, oxygen more power. A scientific Bod could give us the answer. I had driven the pick-up coast to coast over various terrain, conditions and temperatures, but the time spent in Colorado seemed to be more rewarding regarding distance travelled to gas consumption. Great if one has definate figures, the truck seemed to fly with little peddle, where as I thought I would experience the opposite. From La to Las Vagas cars gasping for air, hiway signs reading turn off air conditioning, my Honda motor cycle with an inlelligent carburetor ran along at 65 mph no problem.

 

[Sean Flanagan]

Normally, a non-turbocharged engine will give you about 15% less power, just in Denver, because there is less oxygen. I take my boat to some Mountain lakes at about 8000 feet. This poor old 1980 140hp Mercruiser probably only puts out about 100hp (at least it feels like it).



Luckily, our trucks are graced with a Turbocharger that more than make up for the lower air density.



I remember the old days of the old crappy non turbo GM or VW diesels going 20mph up the hill spewing sooty black clouds because they were tuned for sea level.

 

[DonovanM]

What am I Doing Wrong?

I am definitely not seeing the same results all of you are describing. I've owned my '05 CTD for almost two years now. Until about a month-and-a-half ago, I lived at sea level in southern Maryland and commuted into DC (about 30 mi each way, with about 5-10 mi of stop and go). Just after the new year, I moved to Colorado Springs, CO (about 6500 ft above seal level). I now commute about 16 mi each way, mostly open road with speed kept at around 60-65 mph. On a "bad" day I might have about 1/4 mile of stop and go traffic.



I've kept a log of every fill-up using the computer spreadsheet posted elsewhere on this site, and during my time in MD, I averaged about 17. 8 mpg. Since moving to CO, I've noticed over the past 4 fill-ups that my mileage has dropped to a high of 16. 2 mpg and a low of 14. 9 mpg.



Other than no longer having to deal with congested DC driving, my driving style is the same. I also did a complete fluid and filter change on the truck before moving here.



I figured that the onboard computer would adjust for the higher altitude, but I'm at a loss as to why I am losing between 1. 5 and 3 mpg. Oh, I also keep my truck plugged-in at night and don't let it idle to warm up. Do I need to get something adjusted to compensate for the higher altitude? Any suggestions???

 

[Johnstra]

CO is on winter fuel now. You'll see a 2+ MPG improvement in the spring.

-john

 

[BrianJ]

Same reason a golf ball flies a greater distance in Colorado vs, Florida... less drag from the lower partial pressure of the atmosphere. It's also why you become "winded" sooner when you exercise at altitude - less atmospheric pressure in your lungs to force the oxygen into your bloodstream. Even my crummy Dakota achieved decent mileage in Colorado and Utah!

Sorry folks, but you will not see better economy in Colorado (or other areas of high elevation) due to the thinner air density. As far as why people get "winded" at higher elevation, the lower level of oxygen is more of a factor than atmospheric pressure. While the lower oxygen level is the primary cause, both can and do contribute to elevation sickness.



And guess what, the same thing that starves us humans for oxygen at higher elevations also starves an air breathing engine, much more so than a small benefit of reduced air drag. Don't believe me, take a look at speed and ET results from the NHRA Mile High Nationals compared to any other track/location around the country, they simply cannot generate the speed and power that they can at lower elevations. I spent seven years in the motorsport division of a local company that has an NHRA drag team and the numbers here locally (Bandamere Speedway) don't even come close when comparing to every other track. If I took the logic from several of these posts the ET's and speeds generated in Denver would blow away the other tracks around the country, simply NOT the case in any stretch of the imagination.



Personally, what I see as the reason for better economy, especially driving in the mountains, is the up and down grades that obviously burn more fuel going up, but burn little to nothing coming back down, and winds tend to be less of an issue driving in mountain valleys than accross plains more exposed to any wind. Also, on most mountain roads speeds are more limited than flying down wide open stretches of open highway, i. e. lower speed equals better economy.



So while an object such as our CTD's may coast a little better at elevation, when it comes to generating power to move it any gain is far offset in less engine efficiency.

 

[BHolm]

There is exactly the same amount of oxygen in the air at altitude than not. the air itself does not change. The pressure is the difference. We get winded because our lungs, the bodies air pump, has to work harder to get the air in and out which requires more muscle, hence getting winded.



I brought my 12 second Buick from MN to CO and lost 1. 5 seconds in the quarter, most of it by the first 60 ft. The engine lost a bunch of bottom end. Without forced induction, it was a pooch down low, where it used to rock. As rpms rise it would make OK power but it is the air pressure that is the issue. Whoever told you it was oxygen content was wrong.



I also have run these trucks extensively in both places, 1000 ft in MN and 8000 ft in CO. There is no doubt they get better milage at altitude. All hand calculated, it is a 1. 5-2 mpg improvent. Power is noticably better down low but economy is better up high.

 

[AMcCormick]

You guys are basically saying the same thing, the air is thinner less dense, less oxygen at altitude than at sea level. I personnally dont understand how an engine could get better mpg at altitude. Just a thought, with the lower amount of 02 availible is the engine injecting less fuel in order to keep combustion ratios similiar. Thus burning less fuel but losing a small bit of power. I agree with the air density= less drag theory. I can feel differences in airdensity windsurfing. Windy day in San Francisco and windy day in say Antigua the true wind speed will be the same but you feel more breeze in SF due to the denser cooler air.

 

[BHolm]

READ CAREFULLY, THE AIR HAS EXACTLY THE SAME AMOUNT OF OXYGEN IN IT AT 1000 FT AS IT DOES AT 10,000 FT.



My truck makes less boost at altitude, 35-38 where it will run 40-42 at near sea level.



I guess trying to PROVE I get better milage at altitude is pretty futile. I have ten of thousands of miles of experience in 10 different vehicles that says I get better milage in the mountains. Believe it or not I guess.

 

[BrianJ]

Basic high school physics - the amount of gas dissolved in solution is a function of pressure. At higher elevations there is less barometric pressure and so less oxygen is dissolved in the air you breath. In Denver which is about 1 mile high there is 17% less oxygen in the air than at sea level. At 8000 feet the amount of available oxygen is 25% less than at sea level.



At sea level, the air we breath is about 21% oxygen. At 10,000 feet elevation, the air drops to 14. 5% oxygen. When someone goes from sea level to 8,000 feet elevation, a person's blood oxygen saturation can drop from 96% to 90% and can cause Acute Mountain Sickness (AMS). At 10,000 - 12,000 feet elevation, a person's blood oxygen saturation can drop to 80%.

 

[BrianJ]

In other words, an engine can breath a certain amount of air, however you want to measure it. If you have a litre of air at high elevation, it will contain less oxygen molocules per litre (by volume) than a litre of air will at sea level.

 

[klenger]

If you don't believe a moving machine (vehicle or airplane) can get better fuel economy at higher altitudes, then why do airplanes with turbochargers, turbofans, or turbojets get much better fuel economy at high altitudes. They don't fly at 35,000 feet because the view is better. Thinner air = less resistance. The turbo makes up for the lack of air pressure (within reason).

 

[BrianJ]

Again, I can use the same argument about NHRA dragsters to contridict your statement, and at least they are more similar in nature to a vehicle vs an airplane, which really is not comparable.



Same question you pose, why are they slower and why do they make less power at higher elevation?

 

[klenger]

I agree that a full open throttle, that the engine will make less HP, but driving a turbo-diesel truck around at low throttle hardly lacks for power. We're talking about fuel economy here, not performance. What does hurt fuel economy at high altitudes are the steep grades. It's hard to find long stretches of level highway (South Park being one exception) at high alitudes to see the gain in fuel economy without seeing the losses due to the grades.



Having lived in Colorado for 27 years, I'm not foreign to high altitudes.