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.
Best mileage is with the AC off and the windows up :-)
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
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.
On 30 Jun 2005 11:05:23 -0400, firstname.lastname@example.org (Roy Smith) wrote:
They did an episode of that "Mythbusters" show on that very thing. At
first it seemed like they were the same, but when they took identical
vehicles on a track and tried running them until they were out of gas,
the car running AC lost by a large margin. Seemed that the drag from
the open window wasn't nearly as much of a factor. They only tested
one make, though- I would imagine the body style has a lot to do with
how much drag is really there.
The tests are simply that--tests. What bearing they have on actual
driving results is minimal, at best. Their only value imo is to compare
gross differences between themselves, but in most cases that is
self-evident anyway. Miniscule differences between models, otoh, while
perhaps "statistically significant" in the scope of the test, will be
completely overshadowed by the difference in conditions between the test
environment and actual usage.
That's a good question- the mfg sticker claims 35-51 hwy mpg. I have
no idea where the table came from in the first place. Could be they
used some kind of test that had nothing to do with real-world
Be very careful with this one. I installed one backwards by mistake and
my MPG decreased by 35%. Called J.C. Whitney and they straightened me
out. Said to either R&R the magnet properly or drive backwards to
achieve the higher MPG
Funny thing - Following a recent engine swap, I've suddenly got a wonky
speedo, which is of course making the odometer less than reliable. I filled
up the tank the other day, and checked the mileage. A quick bit of math led
to around 84 MPG. That's one goddamn fine engine I put in there! :)
How do the new speedometer/odometers work? Same computer as the engine
perhaps? I know I can push a button and instantly change all the gauges
from English to metric and the speedometer needle pops right up to the new
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