SMac770

I noticed on a food run tonight that my mileage seemed to be up a hair after doing some work on the car. So I was checking the mileage during the trip, including the part where it dropped from 26mpg (trip computer) to 22mpg while I was sitting in the drive through. Granted, they were real slow tonight for some reason so the trip consisted of a 15 mile / 20 minute drive out, 18 or 20 minutes crawling through the drive through, then another 15 mile / 20 minute drive back. Working out the numbers (very rough, statistically), fuel usage seemed to be about .57 gal out, .11 gal in the drive through, and then .52 gal back (home is a lower altitude than town by several hundred feet, so not unexpected).

I had used VCDS to log some parameters, including fuel consumption (IDE00371), on a prior trip. While sitting in the drive through (so like a drive through or at a stop sign, car is in drive, not park), parsing the log in Excel showed an average 1.38 l/hr for fuel consumption (in drive, stopped, A/C off, engine at normal temp), or roughly .36 gal/hr. That comes to about .12 gal for 20 minutes. So seems to back up the trip computer math. When in drive but stopped, the engine is revving between 780 and 800 rpm. Both trips were around 80 degrees outside, which seems to be when my car performs best for mileage.

So now that I have an idea of how much gas I use idling in drive, the question becomes is it what it should be. Anyone else logged their fuel consumption during a stopped but in drive interval? Mine seems like it might be on the high side, but not enough to start digging into the engine (again).

sasikals26

I have just measured my millage from tank to tank, Filled the tank and drove for 500+ KM and then filled the tank again and calculated the millage, It is consuming roughly(with A/C) 10-12 L/100 KM (2.90589 Gallon for 62.13 miles)

This i have done several times in city and highway driving with my 1.8 Audi a4 B8 2008.

audi8k

1.4l/h without A/C seems high, even though also the load on the generator charging the battery etc will make a difference. I have a B8.5 (which shows the momentary consumption in liter/hour when not moving). I always change from Drive to Neutral when stopped (more than briefly) but I tested a while back also in Drive. I also have a different engine (3.0TFSI) so it is not directly comparable but IIRC the display in Drive and foot firmly on brake was in the range 0.6-0.7 l/h. In neutral it dropped to 0.4-0.5l/h. In both cases without A/C. (Objective of my test was only to prove that my S-tronic does not completely disengage the clutch when stoped in Drive, so I didn't save the numbers but I'm sure they were not in your range.) Could be interesting to know what you get in Neutral.

sasikals26

Is this good idea to always change the gear to Neutral at the stoplight? I always leave the gear in Drive and use the break, also i have never used Neutral at all!! - Just Drive, Reverse and Park.

audi8k

I can amend my previous post by adding that I looked today at my momentary consumption when stopped, and indeed it was higher. Around 1.2 l/h when stopped and in Drive (and around 0.8l/h in Neutral) and with A/C on, over 2l/h.
This was after a short drive so I think the higher consumption is due to battery charging (heavily using park ventilation and cooling box while parked). To clarify why I don't keep it in Drive if I not foresee to take off in a few seconds, it is primarily to save my S-tronic clutch from unnecessary wear. (And instead allow some more wear on the gear mechanism.) There are videos on youtube that states that dual clutch gearboxes disengage the clutch when stopped with foot on the break. Not true in my B8.5 A4 3.0TFSI.

SMac770

I'm not wondering about being a treehugger, just whether then engine is close or far from typical operation. I only kill the engine if I know I'm going to be there at least a minute and will have some heads up that it's time to move again (eg, the drive through person giving me my food, but not the street light turning green).
It seems like mine might not be optimal, but good enough to ignore.
I find it annoying that newer cars' stop/start is enabled by default. When I come to a drive through or school pick up line or something like that where the wait intervals are random and possibly long, then I would turn it on then. But having the car turn off the second it stops moving as I'm trying to pull out onto a street, etc, is just absurd and a long term maintenance problem. Also, I don't get why the engine needs to kick back on when I turn the steering wheel but still have the brake down since they all are electric racks now. Not that the automakers care about your problems past the end of warranty. So long as they save 10 cents per car on the EPA bill.