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Pontiac G8 GT Real-World mileage

14 messages,  Last post on Aug 26, 2009 at 6:36 AM

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What is this discussion about? Pontiac G8, Gasoline, Fuel Efficiency (MPG), Sedan


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#5 of 14
Re: V6 MPG [quietpro] by whoosierdaddy
Jul 17, 2009 (12:47 pm)
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Replying to: quietpro (Jul 17, 2009 10:23 am)

I have read that too, a couple of places, and now just stop when it clicks. I had been OCD about hitting an even-dollar number for so many years...one of those habits.
 
Also, my 3.6L V6 just seems to run a little smoother on 89 octane than 87.
#6 of 14
Re: V6 MPG [whoosierdaddy] by quietpro
Jul 17, 2009 (3:43 pm)
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Replying to: whoosierdaddy (Jul 17, 2009 12:47 pm)

http://www.epa.gov/donttopoff/
 
Don't know why I didn't just look sooner. The only reason on the site that applies to me is that if you overfill, once the gas heats up, it may evaporate into the vapor collection system. The education program on this is terrible. I always figured the only problem was having gas run over the top. Well, I'll try to resist the urge to even out the dollar and see if the trip computer matches my future driving.
#7 of 14
MPG drop by whoosierdaddy
Aug 10, 2009 (1:38 pm)
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My last tankful, evenly-mixed city/suburban/hwy driving, came in at 13.8 on the DIC (V6); about the same doing the math at the gas pump. I thought MPG would get better with time, not worse. Normal driving, not especially agressive, but all with A/C in the recent hot weather. Love the car so I'm OK with it unless gas goes back up to $4+.
#8 of 14
4 cyl mode.. Re: Pontiac G8 GT Real-World Fuel Economy [quietpro] by rayainsw
Aug 13, 2009 (3:51 pm)
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Replying to: quietpro (Jul 13, 2009 5:26 am)

"On the subject of fuel economy, does anyone know of a way to positively determine when the engine is operating in 4-cylinder mode? "
 
Hold down the enter key while cranking.
You'll enter engineering mode where you can see several different displays - including 4\8 cyl modes...
- Ray
2009 G8 GT 11,000+ miles...
#9 of 14
Re: MPG drop [whoosierdaddy] by whoosierdaddy
Aug 14, 2009 (2:34 pm)
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Replying to: whoosierdaddy (Aug 10, 2009 1:38 pm)

It was the A/C. Similar 90 mi drive without A/C yielded 10 mpg better. I would expect a 3 or 4 mpg hit for A/C, but 10 is excessive so will make another trip to the dealer.
#10 of 14
A/C ? Re: MPG drop [whoosierdaddy] by rayainsw
Aug 14, 2009 (4:22 pm)
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Replying to: whoosierdaddy (Aug 14, 2009 2:34 pm)

"It was the A/C. Similar 90 mi drive without A/C yielded 10 mpg better. I would expect a 3 or 4 mpg hit for A/C, but 10 is excessive so will make another trip to the dealer. "
 
I would actually expect no more than 1.0 or 1.5 MPG difference.
Good luck!
- Ray
Ran a few experiments, with & without A/C, early on....
#11 of 14
Re: MPG drop [whoosierdaddy] by quietpro
Aug 22, 2009 (9:06 am)
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Replying to: whoosierdaddy (Aug 14, 2009 2:34 pm)

Was the 90 miles made in one trip both times? Are you using the remote start? I can't think of any way that the A/C could drag that hard on the car and you not know it immediately (excessive drag). I'm wondering if there is some other factor involved. Any chance you used E85? It's definitely worth looking into with the dealer unless it's something that can be easily explained. Crazy!
#12 of 14
Re: MPG drop [quietpro] by whoosierdaddy
Aug 22, 2009 (5:19 pm)
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Replying to: quietpro (Aug 22, 2009 9:06 am)

One trip on 2 different days with starts & stops, not identical trips but similar. No remote start, not E85 (89 octane w/10% ethanol) no other variables other than A/C or no A/C. MPG checked at the pump doing the math. I check MPG regularly and it varies from a low of 13.8 to a best of 27 on a hwy trip about 68 mph no a/c.
#13 of 14
Re: MPG drop [whoosierdaddy] by quietpro
Aug 24, 2009 (7:30 pm)
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Replying to: whoosierdaddy (Aug 22, 2009 5:19 pm)

Hmmm...not a likely explanation but sometimes gas stations' pumps aren't accurate. Any chance of that? It's worth checking out with the service department but I'm guessing they'll be stumped too. Then again, they may find an anaconda stuffed in your intake.
#14 of 14
Re: MPG drop [quietpro] by whoosierdaddy
Aug 26, 2009 (6:36 am)
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Replying to: quietpro (Aug 24, 2009 7:30 pm)

MPG has not been that poor since. Perhaps it was a stackup of minor errors & variables. I drive a lot, and have been getting 19-23 in mixed city/suburban/hwy lately. I love the car, but it will be expensive to drive should gas return to $4.
  
BTW - I never trusted in-car mpg computers, I do the math at the pump. But the DIC in this G8 has been very accurate.

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