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From: hls on 23 Apr 2010 08:15

"Leftie" <No(a)Thanks.net> wrote in message
news:OK8An.43424$Db6.3983(a)newsfe05.iad...

>> I have noticed that my car is getting worse mileage now than it did in
>> the winter. And the fuel blend is the only thing I can think of for
>> that,
>> at the moment.
>
> You are probably also driving a bit more aggressively, assuming that
> you get snow and ice in Winter. You may also have a dirty air filter or
> some other problem. Check your tire pressures as well.

I just serviced the car and it has new filters, oil change, etc. No issue
with tire pressures. We seldom have ice here.

I usually drive at the speed limit, seldom over. My observations are
being made under highway driving conditions. The difference in mileage
is not much, but seems to be repeatable.

From: spsffan on 21 Apr 2010 03:02
C. E. White wrote:
> "hls" <hls(a)nospam.nix> wrote in message
> news:prqdnRcDRrgmOVDWnZ2dnUVZ_qmdnZ2d(a)giganews.com...
>> "ACAR" <dimndsonmywndshld(a)yahoo.com> wrote in message news:02755dcd-
>>
>> If you do a little web searching on your own you'll find car A/C
>> systems are a lot more sophisticated than you think. All my cars get
>> their best average MPG in the summer, despite A/C use.
>> ********
>> If this is the case (and I would guess you have measured it
>> carefully enough
>> to be relatively sure of this), are you of the belief that running
>> the AC gives
>> you this economy boost? Or is it more likely that summer gasoline
>> blends,
>> or perhaps average operating conditions (temperature, humidity,
>> etc), cause
>> the effect?
>
> The extra fuel required to operate the A/C is trivial and is easily
> masked by the factors you mentioned and many others. Here area few i
> can thingk of:
>
> * Car are more fuel efficient when warmed up, so anything that reduces
> warm up time will improve fuel economy.
> * Rear axle and transmission fluids are less viscous when warm,
> resulting in lower gear train losses in the summer.
> * Rubber is more flexible when hot, so the tires use less energy to
> "flex" when rolling.
> * Summer and Winter fuel blends are different, so that can make a
> difference.
> * You use your headlights more in winter, which like the A/C, requires
> additional power.
> * Summer driving probably involves less bad weather driving (driving
> on snow and wet roads decreases fuel economy).
> * Warm air is less dense, slightly lowering air resistance.
> * You are more likely to take longer highway trips in warm weather,
> biasing your fuel economy more towards the highway mileage.
> * Becasue driving conditions are better, commuting probably involves
> less stop and go driving in the summer.
>
> Etc. Etc. Etc.
>
> Plus, don't forget most cans run the A/C in the winter when you turn
> on the defroster if the outside temeprature is above 40F. So even if
> you are not using the A/C...you are.
>
> Ed
>
>


You left out the most important factor. If you turn the A/C off, you
open the windows, greatly increasing drag. In modern cars, the air drag
from open windows is greater than the draw from the A/c. This is of
course more so at higher speeds. And it probably doesn't matter much on
some non-aerodynamic boat like say, a 1964 Cadillac. But on a Camry (or
most other cars) of the 1990s or newer, it is another story!

Regards,

DAve
From: Leftie on 23 Apr 2010 00:45
hls wrote:
>
> "Leftie" <No(a)Thanks.net> wrote in message news:suuzn.137891
>> Yes, yes, and maybe a few. I do it manually, switching the AC off
>> to accelerate and back on at cruising speed. Don't open the windows
>> wide instead, though, because that causes as much drag as running the
>> AC with the windows closed, at highway speeds.
>
> I wouldnt waste my time manually switching off the A/C unless there
> were another reason than economy to do it.
> Driving a car with the windows open will likely cost you a little in fuel.


I've done it for more then 20 years. Our '95 4 cylinder Camry sedan
gets from a low of 27 mpg in Winter to a high of 34 in Summer, in
driving that is about 3/4 highway, 1/4 city. The A/C consumes
significant fuel when the compressor is engaged while you are
accelerating. Simply avoiding that situation removes most of the hit on
fuel economy from the A/C, while still keeping you cool.

>
> I have noticed that my car is getting worse mileage now than it did in
> the winter. And the fuel blend is the only thing I can think of for that,
> at the moment.

You are probably also driving a bit more aggressively, assuming
that you get snow and ice in Winter. You may also have a dirty air
filter or some other problem. Check your tire pressures as well.
From: ACAR on 21 Apr 2010 08:03
On Apr 20, 8:57 am, "hls" <h...(a)nospam.nix> wrote:
> "ACAR" <dimndsonmywnds...(a)yahoo.com> wrote in message news:02755dcd-
>
> If you do a little web searching on your own you'll find car A/C
> systems are a lot more sophisticated than you think. All my cars get
> their best average MPG in the summer, despite A/C use.
> ********
> If this is the case (and I would guess you have measured it carefully enough
> to be relatively sure of this), are you of the belief that running the AC
> gives
> you this economy boost?

Nope, the A/C consumes some engine power.

 Or is it more likely that summer gasoline blends,
> or perhaps average operating conditions (temperature, humidity, etc), cause
> the effect?

I can detect increased fuel economy as air temperature rises.

From: hls on 21 Apr 2010 12:48

"Leftie" <No(a)Thanks.net> wrote in message news:suuzn.137891
> Yes, yes, and maybe a few. I do it manually, switching the AC off to
> accelerate and back on at cruising speed. Don't open the windows wide
> instead, though, because that causes as much drag as running the AC with
> the windows closed, at highway speeds.

I wouldnt waste my time manually switching off the A/C unless there
were another reason than economy to do it.

Driving a car with the windows open will likely cost you a little in fuel.

I have noticed that my car is getting worse mileage now than it did in
the winter. And the fuel blend is the only thing I can think of for that,
at the moment.
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