How much more gas does it cosume when you have your AC on and top off? - 986 Forum - The Community for Porsche Boxster & Cayman Owners

vouvoune · 08-24-2006, 05:12 PM

Anyone knows what the figure is on how much more gas does the Boxster cosume when you have your AC on and top off?
It gets so hot in St.louis sometimes that I just have to blast the AC but was wondering about it while seating in a traffic jam today...Merci, V

08-24-2006, 05:17 PM

I have consulted with Rail26, and our calculations show a MPG decrease of exactly 2.79!

RandallNeighbour · 08-24-2006, 05:31 PM

Vanessa, do you ever let that guy in the passenger seat drive your boxster unsupervised?

vouvoune · 08-24-2006, 06:15 PM

Well that's my little brother and is only 16 years old. He is from France and there we don't get our driver's license until we're 18...So, it is a DEFINITE NO!!!!
In a few years, maybe...when I'll drive a 911

der Geist · 08-24-2006, 06:35 PM

I don't know what the exact figures are but I think that it would be a little more than the 2.79 but that is probably a damn good average. My personal feeling is that it is a little more but most of my milage is stop and go city driving. Interesting note-There was an episode of the Mythbusters wher they drove an SUV around the track with the windows down/air off and then again with the windows up/air on. Surprisingly the SUV got slightly better milage with the air on and the windows up. Mostly due to drag from the windows beingdown. And I always thought I was saving on gas by sweltering!

Perfectlap · 08-25-2006, 10:22 AM

Vanessa, the 986 is a better sports car than the 911. Don't let them fool you or ever try and school ya.

Boxster is mid engine, only the best sports cars in the world have that distinction.

jeffsquire · 08-26-2006, 05:25 PM

Mythbusters (discovery channel) did an episode on this. The consensus is that A/C saves gas versus open windows. BUT, they test drove Ford pickups not Boxsters. Still this may give you guidance.

SD987 · 08-27-2006, 06:53 AM

I too have read that A/C versus windows down is about equal, however, running the A/C is definitely "harder" on the engine (particularly in stop and go traffic). For this reason, I used to roll my windows down when I was stuck in traffic rather than run the A/C, however, in my old age, I find it hard to give a crap.

Even worse, I've been known to run the A/C with the top down and the windows up....and I known I'm not alone in this, among Boxster owners

.

70Sixter · 08-28-2006, 08:46 AM

Quote:

Originally Posted by SD987

...I used to roll my windows down when I was stuck in traffic rather than run the A/C, however, in my old age, I find it hard to give a crap.

Even worse, I've been known to run the A/C with the top down and the windows up....and I known I'm not alone in this, among Boxster owners

.

I confess to the same sin.

MNBoxster · 08-28-2006, 09:05 AM

Hi,

If you choose not to run the A/C, be sure to run it at least 3 min./mo. to recirculate the oil in the compressor to maximize it's lifespan, and those of the 'O' rings...

Happy Motoring!... Jim'99

Phill Dougan · 08-28-2006, 10:51 AM

I recently turned my air con off around town on my 987 and the computer is telling me its gone from 25mpg to 29mpg. so its a costly item around town. my son has a 986 and he gets 29mpg with it off.I now drive with it off in all but the most nessasary conditions.

mtch · 08-30-2006, 05:31 PM

Quote:

Originally Posted by jeffsquire

Mythbusters (discovery channel) did an episode on this. The consensus is that A/C saves gas versus open windows. BUT, they test drove Ford pickups not Boxsters. Still this may give you guidance.

I have been researching this windows down vs windows up + AC, and so far there is no rule that applies universally. I've read report findings and I've done it myself on many vehicles. My sample size is very small, evening including the reports I read, and my route has not been consistent. Generalizing I would say that sports cars have very little difference, economy cars tend to burn more with windows up + AC, and trucks and SUV's do better with windows up + AC. All of my own tests were on highway only.

I've observed many car I've owned and many that I've had access to over the years. I started this while in college and have kept notes on it ever since

I'm inclided to think that sports have excess power at highway speeds and are so aerodynamically efficient that increased drag of open windows has an equal effect to AC use, but both have little effect. Econo cars usually have "lowish" drag coefficients and low excess power at highway speeds. The increase in drag of open windows has a less detrimental effect than the AC power loss, so running the AC and maintaining highway speed burns more gas. Trucks and SUVs have excess power and really high drag coefs, so the AC power loss is almost negligable compared to the increase in drag.

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