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2015 S8 MPG

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Old 07-18-2018, 07:10 PM
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Default 2015 S8 MPG

Anyone here with a D4 S8 want to share their typical MPG data?

Ive been getting terrible mpg. Driving like an old granny I can get 15-17. 17mpg being a lot of highway driving and 14-15 a lot of city driving.

Im starting to think that something may be wrong with the car. My S8 is a new purchase so I wanted to know what everyone else is averaging so I can compare.
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Old 07-18-2018, 08:17 PM
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yep, something is wrong.. I have same year and model and get about 23-24 on highway driving and about 19-20 for mixed highway and locals stuff.
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Old 07-18-2018, 08:25 PM
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Iím getting about the same as Kbrookings. Have you checked the obvious stuff? Time pressure, air filter, etc?
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Old 07-18-2018, 09:58 PM
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17. And in context...520 HP stock we might recall, or rather more like 575 actual after the spec sandbagging so it didn't look like the RS7 numbers wise... 17 at that real life HP is not so bad.

But question is honestly too simplistic. It is very much a function of city (or now worse--packed urban traffic), suburban or highway (and packed or actually open highway...). Look at your average speed in trip computer as the best correlator and how to try to normalize the data. For my 17MPG, it will be like 22-24mph. And BTW, since 2015 city rating was 17MPG IIRC, at 22-24MPH I would say I just about checked that City MPG rating box in the real world nightmare traffic the SF Bay Area rat race has become. Meantime, if I do more like 35 or 40 AVE speed the number is around 20. If 80-90% highway miles and I am :"keeping up with traffic" and hit an AVE speed of close to 60 (with a bit of stop and go, bit of town, etc.) then out to about 24. And yes, if I held it to 70 (65 yet a bit better) and just stayed on the open road except for fast food breaks at roadside, I can get close to the 27 highway rating for 2015's. 2015's also had slightly better EPA ratings than most other years.

Also, if you live in an Ethanol state, that could be another MPG ding. Thank you farm lobby. WA is perhaps one, just like CA. 91 octane we have (some have 93) is probably good for a percent. Even those 21" stock boat anchors on the normal S8 (I ditched mine) are good (bad) for 1-Ĺ or 2% for money down 21" rat hole...

If I didn't make your day already, be sure your trip computer is actually calibrated if that is your data source, or use actual tripmeter miles/gallons pumped. Audi is better than many, but trip computers are invariably feel good funny math. My correction factor was a 6% reduction on the S8 IIRC. Numbers above I quote for my 2015 S8 are after I dialed in the correction factor to VCDS. Mine now typically reads within 1% when I cross check it. Again, Audis are better than ave for how much they lie to you on the MPG screen. A prior Toyota and a Chrysler were both up there with 15%+ bogus MPG trip calc. errors. Thus, if that is your data source, not only is the S8 one probably 5% + high stock as a guess, but you have already been in a possibly yet more warped differential distortion field with other prior vehicles.

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Old 07-19-2018, 04:38 AM
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I havenít been able to check anything yet. Day 2 of owning the S8 half the tank was already gone.

My previous car was a G37 coupe and I was averaging 18mpg on that car but I was abusing that car every single day I drove it. Mostly city miles too. 80% of the time was in sport mode and only filled up once every week daily driving it.

Comparing my S8 I have to baby it and keep it under 3rpm and drive 90% highway to average the same and canít daily drive it.

tbh I was expecting to be able to floor it here and there every once in a while and average the same mpg as my G. I do understand that the S8 has 2 more cylinders and 2 turbos but I remember my first car was also a 2002 Audi A6 4.2 V8. Same story there; I abused the shiz almost every day and still averaged better than the 2015 S8 driving granny style.

Do any of you guys daily drive your S8? How long does a full tank of gas last you?
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Old 07-19-2018, 06:06 AM
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If you're 90% highway, you should be over 20mpg unless you're driving 90+ mph or doing 3rd/4th gear pulls repeatedly. I use mine as a daily driver and have a 45 min commute which is about 1/3 highway and 2/3 stop & go. I average mid-teens when traffic is heavy and high teens when it's light. If I do a grocery store run (5-10 minute drive), I'll get 12-13 mpg since I'm usually hitting it hard on the way. Timing is fillups is relative to the commute distance so not sure that feedback will benefit you.

That said, I definitely fill up more frequently than my B8 S4. But, it doesn't feel like I fill up any more than my B6 S4 (V-8) that I drove over a decade ago. For the time that I drove it, I averaged around 17 mpg which is about what I'm averaging on my S8 which has double the HP (APR Stage 1).

Whatever it is, the benefit outweighs the additional fuel cost - so much so that I never think about it. I just wish I had a bigger tank!
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Old 07-19-2018, 07:46 AM
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Well variously, if you were reading trip computer off G37, it could well have been 15% optimistic, vs. maybe 5% on the S8. That could be 1-2 MPG's all by itself. Then there is the V6 vs. V8, which means real comparo car is 3.0T...and actually more an A6. S8 will also weigh in at probably half a ton over a mid sized one axle drive ride like that. Having owned a 2000 A6 4.2, it was actually in same league MPG wise as S8, and on open road best my C5 4.2 could do was about 24MPG's (calibrated...). C5 4.2 weighed about 600 lbs less than the quote porker S8 too--just over 4,000 back then. Then there is the blow the doors off it part...whether G37 or old 5 speed AT 4.2. Even a D4 3.0T A8 will take a C5 4.2 all day long and will pass it at the pumps too. It will hold its own in general against a D4 4.2 for that matter. Meantime, D4 S8 is literally up there on a top 10-20 type fastest production list.

Anyway, take the time to do some actual miles/gallons calcs, and enjoy ride along the way. As mentioned, you will probably see that the average MPH reading is the best correlator to how the MPG's are doing tank to tank.

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Old 07-19-2018, 08:07 AM
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I don't have an S8, but an RS5, so V8 as well, albeit naturally aspirated and slightly larger displacement. My lifetime average over 5 years and ~62k miles is 15.3 mpg. That's a combination of driving the snot out of it and long road trips as well as daily driving, but no commuting and rarely stuck in traffic. It also includes 4000 miles in Europe with lots of top speed Autobahn driving. Compared to my previous B7 S4 that's about 1 mpg more than I managed to average over 8 years and ~80k miles. On a very very long road trip with car in comfort and ACC engaged and no traffic and doing 75-85 mph I can average 23-24, but that's rare. Most road trips I do 20-21. The S8 is heavier, but has the benefit of COD, so the more often it shuts off 4 cylinders the better the mpg should get, so perhaps you should start paying attention to whether you are cruising in 4 cylinder or 8 cylinder mode. Don't drive around in Dynamic mode all day for starters. But in general your numbers don't surprise me. It's still a 4 liter V8 moving a barge around at the end of the day. But definitely as somebody said, check your tire pressure. Can make a big difference.

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Old 07-19-2018, 09:11 AM
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Iíll get everything checked out. Kind of hard to believe that driving it extremely economicaly and feathering the gas pedal would have such a low mpg.

I filled up yesterday and reset my trip meter and will calculate the mpg by hand at the end of this tank. 100% of my driving is in comfort mode.

i wouldnít be complaining about the mpg if I was driving hard. I mean I want to drive hard from time to time but the day that I did push the car a little I spent half a tank of gas.

i drove about 115 miles 92% of it on highway and half the tank was gone. Pushed it maybe 3-4 times and then granny driving the rest of the way.
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Old 07-19-2018, 10:09 AM
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Originally Posted by Trust93 View Post
I’ll get everything checked out. Kind of hard to believe that driving it extremely economicaly and feathering the gas pedal would have such a low mpg.

I filled up yesterday and reset my trip meter and will calculate the mpg by hand at the end of this tank. 100% of my driving is in comfort mode.

i wouldn’t be complaining about the mpg if I was driving hard. I mean I want to drive hard from time to time but the day that I did push the car a little I spent half a tank of gas.

i drove about 115 miles 92% of it on highway and half the tank was gone. Pushed it maybe 3-4 times and then granny driving the rest of the way.
The best mpg you can get is if you can cruise at constant speed on a highway with no elevation changes. What lowers the mpg is slowing/down and speeding up due to traffic or increased power needs due to elevation changes. The rated economy is something like 14 city and 25 highway and mixed average of about 19. Looks like your city driving is pretty much on the dot, and I'm guess your highway driving involves traffic and possible elevation changes. Also at what altitude are you, that makes a difference, too. Also, did you drive yourself on those 115 miles or did you engage ACC. ACC will most likely manage better fuel economy.
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