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By way of review, last August I was able to purchase a 2001 Insight 5-speed with only 29K on the odo at the time. I am less than a month away from owning it one full year. At the time of purchase, we were still in some very warm weather here in Albuquerque and I was able to gain quite a bit of experience with operating the A/C in Eco mode v. Auto and in establishing what techniques contributed to good mileage. Up to the winter season and the arrival of lower BTU winter gas, I was able to average mileage in the high 50s over the course of a tank.

Through the winter, I was rather astounded (though surely not disappointed) to find that my tankfuls (covering essentially the same driving profile) were breaking 60 mpg. I was able to sustain that performance into the Spring.

About two months ago, however, mileage started to plummet. My last full tankful returned MPG in the low 40s and right now I'm 1/4 into my current tank and it has taken some real work on my part to raise the tank's avg to even 48. The tire inflation is good and the gauges show nothing out of the ordinary in terms of battery charge, assist, level of charge, etc.

However....there is one thing that changed at the same time and that's the part of town in which we live. We moved all of 6 miles and we are fractionally higher in elevation than we were before (5200 feet v. 5130 feet) but, more significant, I think, is the fact that the main commercial area that I frequently run to for coffee, the bookstore, etc. is now only two miles away as opposed to 6 miles away...and almost 200 feet lower in elevation than the new house.

I've begun to suspect that it's a problem that my morning run *to* this area is largely downhill while the return is, therefore, mostly uphill. This means that my one downhill run is essentially being "wasted" during the period following a cold start, meaning I get little benefit from it. Meanwhile, the return trip later in the day, which is essentially another cold start, is hit with the double-whammy of having the uphill climb (and against a number of traffic lights which often mean accelerations from a dead stop).

Do any of you have experience with similar conditions that might validate my analysis? If this is what is truly happening, I can live with it. I'm certainly not going to go out and use up more gas driving around just to try to pull up my average (though I realize that a long drive or two every now and then would be a good thing for the engine). But I'd like to be a little more confident that this is the explanation...instead of some other problem lurking in the shadows.
 

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IMO its the "standard" frequent short trips MPG penality.

Elevation change is _always_ a negative regardless of which way is up. :eek: ;) You never gain as much downhill as you spend additionally climbing back up, i.e. aero and rolling friction losses.

A block heater when used to pre-warm the engine would help increase MPG's some under your conditions.

HTH! :)
 

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I have the opposite problem: My commute is uphill in the morning, steeply at first and then more gradually, and then mostly downhill in the afternoon.

On a really hot, calm day I can just barely get 90 on the way to work (have done it about 5 times) by being really obnoxious and going 45 mph, but can easily get 100 on the way home, coasting perhaps 1/4 of the way. So far my maximum overall, for a 42 mile round trip, is 97. I don't know what was going on that day because I haven't been able to repeat it--mostly I'm in the low 90s right now for my daily commute.

It drops to below 70 in the winter.
 

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I think we're almost "agreeing" here Dougie.

Yes, _all_ newer cars compensate for altitude. But given all the other (virtually) unchanging MPG limiting parameters and _all_ other things being equal (except for what relates to altitude) Higher altitude = lower MPG. But not as much as in older cars (carburated) and its probably even a smaller factor in an Insight since it's "tweaked" for high MPG.

It's not rocket science. ;)
 

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Actually I think we're disagreeing. :eek:

Temperature, humidity, and altitude have a SIGNIFICANT effect on air density, and aerodynamic drag is directly proportional to density. The difference between the air density at sea level at 15 degrees C (about 70 F) on a dry day, compared to 6500 feet at 35 C (95 F) on a humid afternoon, is a bit more than 10%. That translates directly into a 10% reduction in aerodynamic drag.

http://wahiduddin.net/calc/density_altitude.htm
 

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Insightful Trekker said:
MO its the "standard" frequent short trips MPG penality.
k heater when used to pre-warm the engine would help increase MPG's some under your conditions.
Bullock is right abut those short driving runs, they'll devistate your MPG results.

I to live close to where I work and have found that I can easily close out the day with 60 MPG or better readings if in the late afternoon I just go down the road about ten miles or so to check on some properties; get's me out of the office for a little while as well.

Give it a try; nothing ventured, nothing gained.

Fred / Proud Owner of "The Silver Bullet"
 

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Dougie said:
That translates directly into a 10% reduction in aerodynamic drag.
And do the math :roll: The aero drag factor is _not_ significant at speeds below 40 MPH. Therefore depending on the specific drive cycle its "weight" is _no more_ than your dervied 10% and will be lower. Do the rest of the math and you'll see that combustion efficiency factors are higher.

Believe what you want but you can't change the laws of physics.
 
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