Speed, fuel economy

[CharlesW]

This is a follow up on a comment I made in my speeding thread about the difference in gas mileage at different speeds.
Keep in mind that this is a Pontiac Montana minivan which probably compares to your average garage door as far as aerodynamics.

All results were with the cruise control doing all the work.
The computer was reset at each speed change.

1. 20 miles at 60 mph gave me 28 mpg as per the "Average miles per gallon" on the information center.

2. 70 miles at 75 mph gave me 24.5 mpg. (Never had to change a thing for those 70 miles)

3. 12 miles at 80 mph gave me 18.9 mpg. (Ran up on some traffic and had to slow down)

All the above were on the interstate highway.

4. 15 miles of hilly two lane road gave me 24.1 mpg.

Several things surprised me.

1. The small difference in mileage between 60 and 75 for one. 3.5 mpg wouldn't change my driving habits at all.

2. The large difference between 75 and 80 was more than expected. Obviously, the cheese box shape starts to take its toll at the higher speed.

3. The hilly terrain reduced the mileage more than I had expected as well.

As is the usual case with my very unscientific research projects, it doesn't prove a thing and probably is worth almost as much as it cost you.
It was kind of entertainig, though.

Charles

 

[Brenton]

Is the mileage change that different, or is the computer calculations for mileage based on all the factors you spoke of, and not actual mileage.

 

[CharlesW]

Is the mileage change that different, or is the computer calculations for mileage based on all the factors you spoke of, and not actual mileage.

I have no idea how the computer calculates mileage.
It has two mileage modes. One called instant and one called average. I would have to guess that it takes into account the throttle position, speed, distance being recorded by the odometer. I do know that when you are stopped, your mileage is shown as 0, so that make me think that it does take into account the distance being covered. When I periodically check my mileage by the old miles divided by gallons used, the results are pretty close to what the computer shows.

Charles

 

[jaybs02]

Charles,
Your experiment may prove to be a great excuse if you ever get for stopped speeding You can simply state that you were conducting and independent study on the resistance of a garage door at speeds approaching 100MPH for Stanley (or garage door maker of your choice) and your vehicle was the closest thing that you could find :lol

But on a serious note, that does seem like a rather dramatic drop on MPG for only 5 MPH difference

"J"

 

[CharlesW]

But on a serious note, that does seem like a rather dramatic drop on MPG for only 5 MPH difference

"J"

It definitely does, but one thing I remember about my 1988 Chevrolet Astro van, (A real box), it would run 75 at about 1/4 throttle and about 86 at WOT. The wind totally kills a van's performance. I think "van's performance" may be an oxymoron

Charles