slpat

I have had my 2014 A8 4.0T for 6 weeks and have taken it on two road trips - one Houston to Dallas and one Houston to Austin. In both cases i have averaged between 75 and 80 with a few periods of time as high as 90.

I came from a Mercedes E550 and there is no comparison to the power of the engine or the ride on the highway. The surprise to me is the fuel economy. I got 25.7 for the Dallas trip and 25.9 on the Austin trip. The car is quiet at speed and the RPM's are 2100-2200 when you in the 75 - 80 mph range.

Overall an excellent car. My kids voted to take it over their mom's Infiniti QX60 for the trip even though that has TV's. They prefer iPads and seats that recline, massage and can heat or cool!

MP4.2+6.0

Sounds good. But...

Run a calibration of your MPG readout, assuming that is the data source here. That is for a full tank compare trip odometer miles/gallons pumped against the readout. My final correction factor on the 2015 S8 to get to reality was 108. As in 25.7 x 100/108 = 23.8 using one of above data points. Still good in that example for a very strong motor and ride, but a couple MPG's less. Each vehicle will vary. Never owned one that reads pessimistic. Funny how that happens... My correction factors have been from 3% all the way to 15%; both Toyota and Chrysler have gotten that dubious way off end point for me.

slpat

I will verify my last trip. I have the mileage and the tank was full when I started so I will see how many gallons I used and calculate it the old fashion way.

LexusLSguy

Best consistent highway mileage I have seen, according to the computer, is about 34 mpg on my supercharged 3.0 This is over the course of a 50 mile trip. Usually I'm between 27 - 30 on the highway.

KnappAttack

On my 2011 4.2 I've seen an astounding 32-33 MPG using 91 octane with a couple tanks of non ethanol, but generally I'll do 29-30 on 10% ethanol 91 octane running 80 MPH. This is off the computer which is a slight bit optimistic also. I should mention If I baby it and keep the speed down to legal limits on 10% it will do 32 or a slight bit better, but what fun is it if your not passing everyone on the highway.

Very impressive mileage for a large car for sure!

Jack88

I got up to 32mpg indicated with my 4.2, but it calculated out to just shy of 29mpg.

britinmn

W12 averaged 24 according to the (optimistic) computer on the way up to Northern MN this weekend - approx 150 miles, a little stop and go traffic, but mostly cruise set at 62 on single lane roads.... And I "mostly" kept my foot out of it

FA8L

Last night I had a 60mi trip and got 26mpg on my 4.0T. I typically stay around 1700-2200rpm 75-80mph. Was honestly expecting way worse going into this car but have been pleasantly surprised. Anyone have mileage numbers on tuned motors?

slpat

So after a fill up and calculating the mileage it is more like 22.8 miles per gallon. Still a good number for a large car with a V8 and over 400 hp but not quite as good as the car computer.

I assume if you drive in sport and really push it you can get the mpg pretty low.

MP4.2+6.0

From lots of years' experience with the D3 W12--ultimate A8 gas suck--it is the in town driving that kills it. Even fairly small percentages of a total tank in lots of stop light city driving brings it way down. Some effect from 60 vs. 80 type speeds, but much less. Thus best MPG's I ever saw on that one (true/calculated) were 22, with all day on highway and only roadside stops/gas.

Attached are a bunch of D4 S8 tanks I logged for calc to do computer adjustment. You can see the variance w/ ave. speed. SF Bay Area is now very congested so speeds not so good; some notes I omitted have more granularity. Like the two higher speed tanks were definitely spirited driving on a road trip. Mine is now calibrated to sub 1% typical variances so I can look at the screen for "trip 1" type MPG's with good accuracy. Basically 25 or 26mpgs on open flat freeway and light foot is best case and more like 24 generally; though "I can't drive 55" for extended distances to try to max it.