All gassed up

Ergo

Ergo

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Joined
Jul 11, 2013
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4
I commute 125 miles roundtrip each day and can complete 3 roundtrips between fill ups. I have been averaging 38 mpg when not running the A/C. This week, I drove one roundtrip running the A/C and two without. My gas mileage dropped to 34 mpg. What would be the correct formula to determine the true mpg had the A/C been in constant use. Thanks in advance for your guidance.
 
Sure. I approached it this way: There are 3 parts. One with A/C (x) and two without A/C (y). The forumula 1x + 2y = 350 miles. Divide this by 10.8 gallons of gas and you get 34 mpg. But I don't believe this to be an accurate reflection of the gas mileage I would achieve with 3 parts x. There needs to be method to apply factors of 1/3 and 2/3 to get an accurate value. Respectfully, Ergo Edit: Yes, this is me.
 
Ergo said:
I commute 125 miles roundtrip each day and can complete 3 roundtrips between fill ups. I have been averaging 38 mpg when not running the A/C. This week, I drove one roundtrip running the A/C and two without. My gas mileage dropped to 34 mpg. What would be the correct formula to determine the true mpg had the A/C been in constant use. Thanks in advance for your guidance.
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This is a "weighted average" problem. You ran the A/C 1/3 of the time and did not 2/3 of the time so taking x to be the gas mileage when running the A/C, count that as 1/3 and the 38 mpg as 2/3: (1/3)x+ (2/3)(38)= (1/3)x+ 76/3= 34. Multiplying by 3, x+ 76= 102 so x= 102- 76= 26.
 
Thank you for your kind reply HallsofIvy. Seriously, running the A/C results in a 32% reduction in gas mileage?! Sakes. Thanks for the formula. Respectfully, Ergo
 
Thanks for the link Denis. I'm limiting myself by having calculated the mpg on just one tankful. Variables like wind, vehicle speed, acceleration while passing, all come in to play. It would take several trips under a variety of conditions to get a truer value. But based upon this initial test, my mpg with the A/C running is not good. No, not good at all. I think I'll reserve it for special ocassions like when the heat index is 105. My environment may be cooler but my demeanor will be steaming over the lost mpg. :mad: Respectfully, Ergo.
 
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