As some may remember I've been experiencing really bad fuel consumption, average about 20-21 liters per 100km's travelled.

Recently I had to do a trip inland, from sea level to about 1000m above, total of 3500km travelled.

I kept on eye on the altitude on the gps, and from about 500m above sea level my fuel consumption increased remarkably. At the inland altitude I was averaging about 13l/100km instead of 20. On my return home at sea level it immediately returned to over 20.

JK is about a year old with 35000km on the clock.

Any ideas?

 

Higher altitude, less air, you make less power.
It could be that you had to give it more throttle, and it was running rich due to the elevation.

 

My theory is humidity. Hot and humid here in Kansas, elevation 1224ft. Gas mileage here stinks at 13-14 mpg. However, when I got to Colorado every summer at elevations of 8000+ I get much better mpg. This year was 20 average, but got as high as 24 mpg!

 

Just noticed this as I got back from a week in Colorado a 9-11K feet versus 600 feet where I live in S Texas. I got way better economy on the mountain legs of the trip, even with the hills. This was hand calculated, not the in dash computer. Constently got 20-21 mpg, even 22 in Leadville CO. Back home on the flat lands, 18mpg running the same hiway speeds.

 

I am averaging 11mpg (20l/100km), inland this changed to 18mpg (13l/100km), that is a massive difference and hurts the wallet much less!

(Stock other than 285/70/17 and 2" TJM Lift).

Jeep is due for 36000km service and I plan to enquire then.

 

I think two things happen at altitude. The air is less dense so less aero drag which is significant with any Wrangler. The power loss should cause you to run the throttle more open which reduces pumping work for the engine. It is kind of like having a 4 cylinder instead of a 6 cylinder engine.

 

If you have a minute and want to put some thought into it:

..........http://en.wikipedia.org/wiki/Boyle's_law


I'm a Respiratory therapist and Atmospheric pressure and Temp. are a HUGE part of my job. With less At. pressure you have less Oxygen per cubic milimeter. Colder air can compensate for the loss of "volume" but how cold does it have to be?

Less Oxygen = Less combustion and with the same amount of fuel being injected at 2 different atmospheric pressures you will prob. send a lot more unburned fuel out the exhaust with the lesser. I for one have not spent any time in the mountains but from what I hear it's a little more difficult to keep a flame burning. Any input??

 

So I have been meaning to post something up on this, but will just join the bandwagon.

I recently completed a 3,500 mile road trip from Colorado Springs To Anaheim To San Francisco To Tahoe To Salt Lake City to Colorado Springs.

In Colorado Springs, I average about 18 MPG's with a mix of Highway and City (mostly city driving) . Anyways, I noticed a very similar situation in which the lower the altitude and the hotter the climate the more my MPG's diminished. Using the normal tank math, I found that in the SW Deserts of AZ/CA that my avg MPG's came in around 16 to 17 (on the highway, going 65-75 mph). I tried everything I could including ranging between MPH to increase but got nothing. Then as I move up the coast got back in to the 17-18 range. Once I crossed the Northern part of Nevada, my fuel economy dropped to about 16.5 MPG's almost all the way to Salt Lake City.

Then, miraculously, once I gained altitude somewhere around Park City it appears my MPG's went back up. And all the way from Park City, Through WY, Back to Colorado Springs my MPG's was in the 18-19.5 Range.

I thought for sure the lower altitude would boost MPG's and although I noticed a considerable boost in power, did not do better on gas.

So, it got me thinking that the lag in the V6 power I have noticed at home might just be worth the extra MPG's I’ve been pulling. I was however really stoked on the power I got at sea level.

Thoughts?

 

You are correct. "Water Vapor Pressure" is part of the "volume" of what goes into your combustion chamber. Though we don't notice it, we should see a change in fuel economy and power in the winter when the Oxygen molicules are condensed and the water vapor pressure is at it's lowest. The problem is that we lose all the leaves on the tree's which act like wind breakers so we end up combating the wind and thus lose the potential gain.

............http://en.wikipedia.org/wiki/Vapor_pressure

 

Oh and I wanted to ask... has anyone done the MATH to calculate the fuel milage? My fuel econ. says I'm getting 22 mpg but the math says 20. Just wondering if the Oxygen senor might be thrown off by the lack of Oxygen in the atmosphere. I wonder if it might THINK it's burning more efficiently? That's beyond me, next input please!