Just thought I would share this and maybe someone would offer an explanation.

Just took a trip up to Colorado, near La Veta. Altitude is roughly 8600 ft. Spent a week there drove to Denver, Royal Gorge, and a lot of "off the beaten path" places. Truck, 2007 SCREW 5.4 no mods no tuner 125k averaged about 17.6 mpg with 18.5 mpg being the best. I was impressed. Here in the Lonestar i usually get 16-16.5. My half baked theory was the air was thinner and therefore didnt require as much fuel. I was thrilled. Truck ran flawless. We and the grandsons gad a great time. Anyway, just thought i'd share.

 

PS. Mpg was figured by hand not with the lieometer.

 

Sounds reasonable to me. The PCM is going to balance the air/fuel ratio, and, the air is not as dense, so, less fuel can be used.

Glad you visited the "high country"!

- Jack

 

My truck gets considerably better mileage at high altitudes too - even on 85 octane. Best mileage I ever got was between Durango and Colorado Springs, I got 23.2 on that tank. Here in the "flatlands" I have to drive very carefully to reach or break 20.

 

Yeah it is beautiful up there. That was the other odd thing. Gas up that way was either 85 or 86 octane. I never babied it. I watched the accelerations but I cruised at about 75-80. Thething that impressed me was those mpgs even going up and down some of those "hills" lol.

 

You can use a lower octane gas at high altitudes due to the lower air density. Basically, it reduces the effective compression in your engine, since you have less air and fuel in the mix. The lower compression reduces the tendency of the mixture to pre-ignite (knock).

- Jack

 

See I knew I liked this forum. Learn something new every time. Thanks for the insight Jack.

 

I'm confused; when I had my 13 ecoboost and was posting of the **** poor mileage, started life new at 9 mpg and eventually got to a wopping high of 14 mpg highway,i was advised by some of the same posters as here that my mileage sucked due to the high altitude we live at ,6500 ft.

 

Easy pezy to explain. The higher the altitude, the more oxygenates in the gas formulation. It's a chemical way of introducing the oxygen to the combustion process to compensate for the missing oxygen in the lighter air at altitude. Most often though, the engine will run a somewhat "windy" once you come down in altitude since the oxygenated gas is still in the tank. Another high altitude benefit is the lighter air makes the air resistance much less. Think of it as more aerodynamic due to less air friction. Ever wonder why passenger airplanes fly at such high altitudes? Less air resistance, better fuel mileage.

 

Totally off subject, but is there still stuff to do at Royal Gorge since the fire a few years ago? Heard it totally burned everything down except the bridge and a couple other exhibits

 

Hey KRC yeah most of it at Royal Gorge has been rebuilt. Visitor center/gift shop, slides for the kids, gondola ride, zip line, magic show(s) etc.. Its all back. Wife's aunt lives in La Veta and she told us about the fire. It was pretty awsome there. You can still see evidence of the fire in the brush but looks like everything was back up and running. Pretty country up that way.

 

Glad I looked at this and learned a little something else. Still amazes me that higher altitude with the lower octane fuel can aid better mileage than driving in the super flat lands of Missouri for example.