Greetings and Salutation...
On 30 Jun 2005 15:36:49 GMT, Dave Hinz wrote:

On 30 Jun 2005 11:05:23 -0400, Roy Smith wrote:
Edwin Pawlowski wrote:
That's a big drop with AC. Both my cars have 3.8 liter engines and the
difference is no more than 1 mpg. Neither gets 42 mpg and struggle to get
30 on all highway

I believe most cars get better mileage on the highway with the AC
turned on and the windows closed than with the AC off and the windows
open. The added aerodynamic drag introduced by opening the windows is
worse than turning the AC on.

Mythbusters just did this one, actually. Two identical vehicles, one
with AC on, the other with the windows open. It was a Ford Expedition,
which is hardly an example of an aerodynamic, efficient vehicle, but
they found that the one with the A/C ran out of gas first, by a few
percent. I don't have exact numbers, but google might.

This might be vastly different with a more aerodynamic vehicle, where
the aerodynamic change made by opening the windows takes it from "good"
to "bad", rather than from "bad" to "more bad".

Way I look at it, I'll run the A/C and be a bit more comfortable, either
way.

Yea, I saw that episode, and, I think that the BIG issue there
was that they were driving at a fairly low speed. They were limited
to 45 MPH, and, at that rate, I am not sure that the drag would make
a difference. It ALSO might well have been the vehicles. I recall
a sedan from some years ago that got about 15% better gasoline mileage
when driving at interstate speeds, with the A/C on. This was kind
of surprising to me, but, we ran several cycles of testing over tanks
of gasoline, and, it was quite consistant.
Another factor is that the blast of wind through the windows
can be PRETTY irritating after a bit...I much prefer the low hum of
the A/C fans.
Regards
Dave Mundt