Weird fuel economy?

[slalemand]

Just wait until you hear (or read) this.

I did this test over 6 tankfuls of fuel.

3 tanks I filled up and then drove off on the highway, until the fuel milage gauge said 27 MPG or higher. I then drove where ever I needed to. Both highway and city driving. I averaged 22+- MPG on these tankfuls of gas. On these fill ups the gauge pretty much stayed between 21 - 28 MPG

3 Tanks for fuel I just filled up and went where I was going and shut the car down. In most cases, the Mileage gauge said between 8 and 12 MPG was what I was averaging. On these fill ups I averaged 14 - 17 MPG, driving the same amounts city / highway as the other tankfuls of gas? On these fill ups, the gauge pretty much stayed between 11 - 18 MPH.

I did a tank each way i.e., fill up drive highway, fill up drive to first stop.

Is there any chance, the computer has that much control over the MPG on these cars?

I know this wasn't a scientific test, but it sure seems strange to me.

Skip

[doc4point]

I also have noticed this in my 08 XLS. Part (but only part) of the answer may be similar to calculating running batting averages: when you're at the beginning of the season, it's relatively easy to increase your batting average because you're only averaging every new hit and at-bat against a few others. By the end of the season, you're averaging against a whole season of hits and at-bats, so it's harder for a single good game to make a big difference in the average. Same with the way the Avalon averages the gas mileage. That's obviously not the whole answer, because by the end of the tank, you should still have total miles and total gallons, but maybe it explains it some. Otherwise I can't explain it at all!

[TrailDust]

The onboard computer is only as good as its programming. Sounds like a little more work is needed.



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[Shinobi'sZ]

Originally Posted by slalemand

Just wait until you hear (or read) this.

I did this test over 6 tankfuls of fuel.

3 tanks I filled up and then drove off on the highway, until the fuel milage gauge said 27 MPG or higher. I then drove where ever I needed to. Both highway and city driving. I averaged 22+- MPG on these tankfuls of gas. On these fill ups the gauge pretty much stayed between 21 - 28 MPG

3 Tanks for fuel I just filled up and went where I was going and shut the car down. In most cases, the Mileage gauge said between 8 and 12 MPG was what I was averaging. On these fill ups I averaged 14 - 17 MPG, driving the same amounts city / highway as the other tankfuls of gas? On these fill ups, the gauge pretty much stayed between 11 - 18 MPH.

I did a tank each way i.e., fill up drive highway, fill up drive to first stop.

Is there any chance, the computer has that much control over the MPG on these cars?

I know this wasn't a scientific test, but it sure seems strange to me.

Skip

I always calculate MPG by resetting the Odometer on a full tank and then checking it against how many gallons it takes on the next fill up. I drive the same route every day too. I noticed I was getting about 32 mpg (06 Av LTD) with the stock Michelin tires. When I bought new tires I went with the America's Tire version of the Goodyear...the Arizonian.....my mpg wend DOWN about 4 mpg. Lesson learned...it is worth the extra $40 per tire to get the Michelins. But I only got about 35K miles out of them.

[slalemand]

Well folks. I'm back from my trip and have some mileage to share.

ALL Mileage is turnpike miles:

335 first tank - (15.4 gallons to fill)
445 second tank (14.9 gallons to fill)
421 third tank (15.7 gallons to fill)
467 forth tank (15.1 gallons to fill)
398 fifth tank (15.9 gallons to fill)
378 sixth tank (15.5 gallons to fill)
466 seventh tank (17.5 gallons to fill)

2 other tanks for gas where with mostly in town driving and I didn't keep track. I was wondering about highway mileage.

The mileage varied based on Speed and whether or not I was using cruise control. My speeds were 70 - 80 most of the time (at the low end of MPG), and 55 - 65 most of the trip - when I got the best mileage.

Skip