wilfred2k5

Don't be silly. AS/S doesn't affect MPG. You won't accumulate miles while the ignition is off. You would need to track how much gas you're burning from fill-up to fill-up. With aggressive AS/S use, I seem to have cut my fuel costs in half. I do have a brutal commute, though.

I suspect those who pay > $4 per gallon (e.g. Europe) will consider this very cost-effective.

DeerHunter

True, but you do use gallons while idling. Calculated mileage (manual or through the computer) will definitely be affected.

NVThs1

Well my study is done. I can tell you off the bat, that apparently my life is not as boring and routine as I thought it was. Although maybe more calm than I would prefer. I did not run this second tank that close to the first in replicated driving styles. I actually drove on the highway twice on longer jogs. One was 66 miles round trip and one was 76 round trip. These two trips were high speed no traffic, so that boosted my MPG compared to the last tank. It also turned very cold so half my daily work driving was done without the S/S as it would not engage. Without the highway trips I think I would have done worse on the MPG.

Here is my $.02 on S/S. I sill like it. I do think it will save some gas, but not much at all. I think those of us in colder winter wonderlands will not see much if any savings when temps will not allow S/S to work combined with extra power draw from the heat being on. However it is nice to know we are trying to be green with our fun cars. I for one feather my braking as it is, so I am able to better control when my S/S runs or not. When there is a train, I engage it. When I know the light is about to change, I don't engage. If I feel like being peppy off the line and the car is currently off, I start it up before the green hits. Easy as that.

newmoon

Thanks for doing the test and reporting the results. Some of my thoughts:

The average speed in the long-term memory is quite useful to tell how much city or highway driving you do. The time still counts when you are stopped, so if you do a lot of city driving with traffic lights, the average speed will be very low. If you do mostly highway driving, the average speed will be high.

The best mileage is at a steady speed around 55-65mph. It is worse below that because this usually signifies city driving where you use more gas to accelerate, and when idling without the start/stop system. It is also worse above that due to increased wind resistance when driving at high speeds over about 75mph. I have even found that a head or tail wind (measured from the Audi Connect system of course ) can make a big difference of +/- 10% to your mileage at high speeds.

The higher average speed on your second tank captures the highway drives you did, and could explain the increased mileage.

Cold temps do reduce your mileage in many ways besides preventing the stop/start system from activating. People tend to start the car and let it idle for a while. I think the engine also runs rich burning more gas when it is warming up. And the rear window defroster, mirrors, seat and steering wheel heaters all use electricity, placing more load on the alternator, which saps engine power and hence uses more gas.

Also when running any sort of test, if your sample or the number of miles is small, the variance will make it hard to determine the actual mileage. You can get a more accurate reading by averaging it out over more miles.

Below is the long-term mileage of my 2.0T FWD CVT, averaged out over 4,700 miles, and it came to 31.6 mpg. With an average speed of 51mph, you can tell I do a lot of highway driving. But that's not to say I drive at 51mph on the highway. It was actually a mix of about 90% at 75mph and 10% at city speeds.