Hi, I got C2S from 2006 with 30k on it. I bough it a year ago with 21k. Since i remember computer shows gas usage around 12.5 mpg. I'm doing more city driving but still it seams to be high. When I restarted reading and was doing spirited driving it shows around 10 mpg. Do you agree with me that this seams to be low? What could be a reason? I didnt do any mods besides awe headers but reading were similar before the mod. Is it possible that car got changed software which cosign increased gas usage? How i can check if software was changed? Thanks in advance.

 

Wow, that is really low. I think I'm getting around 27 mpg with a mix of street/hywy. Pull into any Porsche shop that has a computer and they should be able to tell you if your software is changed. More will chime in and correct me if I'm wrong, I hope.

J

 

Consistent 24.5 mpg combined city/highway. Yours sounds low on both ends.

 

Averaging about 17 mpg combined city/highway (or what passes for highway on LI). On longer highway runs I can get about 22/24 mpg.

 

I don't think you can compare an 06 and 09 (with the DFI engine).

for me:

15 around town

24 on the highway

8 on the track.

My car is a base 997.1 however.

 

If you're typically in stop-and-go traffic or you are in a city and rarely exceed 30 mph, then you gas mileage is likely to be in the 9 to 15 mpg range.

If you're really getting 12.5 mpg, then you must have to fill your tank every 160 to 200 miles. An easy way to check the computed mpg is to do the math yourself when you get gas. First, you'll have to reset your trip odometer to zero at your next fill up. Then when you fill it again, divide the trip miles by the gallons purchased.

 

Have you calculated your mileage manually to compare to what the computer says?

 

Yes I did math my self and it looks that computer reading are correct.

 

20 mpg for my 07 GT3 RS and 20 mpg for my wife's 10 C4S Cab PDK.

 

2012 Black Edition getting around 15 in city and 24 on the freeway at 85+ mph

 

Seems low to me as well and I don't care about the MPG - I try to get poor mileage! I would have it checked.

 

Actually, that compares quite well with my 997.2S. I think the difference in our 'official' mileage numbers arises mostly from differences in engine response under the formal procedure.

My overall average is 17.5 mpg, but that number depends on the mix of city/highway we each experience. I've never driven exclusively around town, so I have no value for that. Vigorous driving on back roads: ~15. Highway is 24 to 25. Track time is reliably 9 mpg.

I agree the OP needs a diagnosis. Anything as low as twelve implies mostly track time or equivalent high rpm operation, or... something that should be fixed. Without a related component failure, I'm fairly confident about the mileage an engine computer reports. The technique used is at least as accurate as measuring the gas put in on successive fuel stops. Never hurts to cross check of course, but don't expect anything but confirmation. The real answer lies elsewhere I expect.

Gary

 

I am on long island also and have the same results.

 

what you do - while driving on a highway at 6th gear, 3K rmp in the trip section reset your counters in the pcm and see what it will show while cryusinng - it should be in between 22 to 25mpg when you go steady.

if it will be much lower during highway cruise (like 15-17) that would mean issues with valves.
what it shows in city cycle does not matter as every time you start your car counter starts at 9mpg, say i drive my kid to school, it is 12 miles trip so it only gets to 13-15 mpg in the PCM when i end up but it is BS and I know it for sure from how often i need to refill gas tank.

highway test is the good way to see if there are any issues or not.

 

i get 14 mpg on my GTS, mixed highway and city driving