How accurate is the trip / distance til empty calculation? I've only put one tank in my 04 1.8T so far, and going by the trip odo divided by gallons method, I got around 26.5 mpg. The computer seemed to always show over 30.

Is it known to overestimate?

 

Mine seems to always be higher than miles driven/gallons used method. But then again, I have been having misfire issues since December 09, so God knows what mileage I would be getting if my car was working properly.

My question is, when I slow down and stop at a light, why does it say I am getting 200 mpg? Shouldn't I be getting zero? Im standing still!

 

The reason it shows 200 is that during coasting/decel, the ECU shuts off the fuel injectors, so anytime you're coasting, you're using zero fuel, and 200 is as high as the scale goes. When you're stopped, the fuel economy display just doesn't update. That said, if you're stationary long enough, the distance to empty will start to decrease.

I've noticed that my distance to empty tends to be optimistic with a full tank and gradually gets more pessimistic the closer to empty I get. Usually on a full tank, it reads 440 or 450 miles, and I once ran it down until it said I had only 10 miles to empty. I then put in just under 15 gallons (the spec says it's a 17.4 gallon tank, so I should really have had around 60 miles to go).

As far as miles traveled divided by gallons used, my 02 1.8T usually gets somewhere between 26 and 28 MPG when used mainly for highway driving, so your 26.5 sounds reasonable to me. Of course, how you drive and the conditions at the time can change things. (Cold air is more dense, so the MAF will sense higher flow when it's extremely cold out and cause the ECU to add fuel to compensate, for example; this is part of the reason you see worse mileage in the winter; longer warmup time is another.)

 

Oh, I forgot to mention on the 10 miles to empty when it should have read about 60 that I had traveled something like 385 miles on that tank, so the initial reading of 440 or so miles to empty theoretically should have been about right. I think it just gets more conservative in order to scare you into filling up before you're really running on fumes (obviously worked on me).

 

I typically get roughly right around the correct miles to a tank of what the computer tells me. Always use the trip odometer and that way you will never go wrong. As soon as you fill up, reset it and then check again when you go to fill up again. That way you will no for sure how many miles you went on a tank.

 

I agree with all of the above. When I just fill up, it says 580 miles to empty. The real number is somewhere around 460. The mileage calculated to around 26.5 which is within the rating for the car, but the on board display showed above 30 for most of that tank.

I will monitor it for a few tanks just to see what I really get.

 

My experience with my A6 over 130k miles is that it is 10% optimistic. I calculate mpg at actual (miles driven/gallons) and while the computer average mpg shows ~24+ the actual always comes out ~2 mpg less. When I fill it, depending on it's last mpg experience, it shows 430-500+ miles to empty. In reality, I get 380-410 miles per tank depending on temperature and how I drive.

 

Man, all you guys getting 350+ miles per tank make me jealous. When I fill up, it says 480ish miles 'til empty.

But when i get the low fuel light, I am sitting at 260-280 miles to the tank. Only twice in a year's time have I gotten 300+.

Now, I will caveat that with most of my driving is city, and I warm the car up most mornings since I live in Wyoming and we only get warm temps from May-Aug.

 

Double post

 

Almost all my driving is highway. When I'm driving around town, the computer shows ~20 mpg which means I'm actually getting less than 18. And I drive conservatively. But it's a big, heavy, AWD car.