Mark P

This is the first tank I analyzed like this, but it corresponds to the 10th full tank I've had, so titled it accordingly.

I had posted about this while it was in progress, but now I have full tank data to share. Each day, I recorded the Miles Driven, Estimated Miles Remaining, and Avg MPG (for the tank thus far).

I added the miles driven and miles remaining to see what the trip computer was estimating for the full tank. Then I calculated my own estimated miles remaining based on an assumed quantity of fuel that the trip computer covers from full to 0miles remaining, and the AvgMPG of the tank thus far.

Comparing them, I see what I had assumed from prior more casual observations. The trip computer is very optimistic in what it's predicting for miles remaining. I had hoped that changing the accuracy of the fuel consumption would address this, but it has not. My consumption accuracy is now quite accurate, but this is still very optimistic.

I'll track a few more tanks and see if they all have the same trend.

Trip computer would suggest that I'm going to get nearly 600 miles for the first several days before it starts to decrease the estimate as it gets closer to being empty:


My estimation, however hones in on a realistic value quite early on:


Here's the corresponding MPG per day and avg to see how it played a role in the above:


You can see all the data here:
http://ctny.audiworld.com/mark/q5/miles_in_tank/tank10/


I've also begun tracking tank#11 which is showing similar early trends:







You can see all the data for this tank here:
http://ctny.audiworld.com/mark/q5/miles_in_tank/tank11/


If only I had a way to tweak the accuracy of this as well

914Audi

Thanks for the data Mark. I don't have this level of detail (not even close!) but I'm getting close to what the trip computer estimates. After a fill, I regularly see numbers right around 600 miles remaining. While I haven't drained the tank (I tend to fill up on weekends while out on errands), I'm still avg 30.5mpg per trip computer and 29.0 using fuelly actuals. If I assume the 19.2 tank capacity is accurate, that would suggest 557 total miles. .... Vs the 600 usually shown on the trip computer at the start.

I know this isn't precise, but I'm not seeing the same degree of degradation as you are.

I'll try to see if I can keep more accurate data to compare.

MP4.2+6.0

1. Continuing good work!

2. Why are you assuming a 19 gallon tank? The spec for the TDI and all others except the Hybrid is 19.8 gallons. The underlying Euro spec is 75 liters. Only the Hybrid is smaller at 72 liters, or 19.0 gallons. See next point relative at least to Hybrid tank specifically to gauge spec. vs. actual.

3. On my last Hybrid tank, I pushed it as far down to empty as I was possibly comfortable with, with nearby stations along freeway exits I knew as likely bail out points, and an "EV" button fall back. I had already run to 5 and then 0 estimated miles to empty right at the point of a couple of prior fill ups. This time it went to "0" when I had accumulated 470 miles. I then watched the incremental miles as I decided when to chicken out and fill it. I did that at 478.9, or just about 9 miles past indicated "0." Indicated pumped gallons were 19.133; 72 liters being 19.02. I did run the nozzle 2-3 times after first auto shut off though didn't get much more than the last few tenths of a gallon. The net was apparently I did take it down to basically fumes, and also that range below calculated "0" miles to empty was probably fairly comfortably the first 5 miles, but not comfortably up to 10. In that last approx 9 miles was maybe a mile max of EV running. I will start watching estimated range near start of tank vs. what is eventually achieved, but off hand I don't think I ever remember it reporting in the 500's right at fill up. Watching it near the end where I was carefully watching from about 60 miles estimated to empty and sensing the incremental 5-10 miles short of my destination where I figured I would have to concede and fill up, what it was displaying on estimated miles to zero was rolling off pretty consistently with each 5 travelled miles. In the last 20 miles or so, the tank gauge was effectively at empty, so I was relying on the estimated miles to zero as I was pushing ahead.

FWIW, that was one of the better representative tanks (25.03 MPG calculated actual) I have seen. Display indicated was 25.8; an error of -3%, which is also my arithmetic average error now over 9 tanks where I have receipts and log data. Ave. speed on this tank was up at 40MPH while a lot of my tanks have ave. speeds only in the 20's. I get the sense from the qualitative descriptions in various of the MPG posts that I have a meaningfully greater slow speed mix than many.

Mark P

I used 19 based on roughly a number I recalled seeing when I filled up right when hitting 0 miles remaining. I recall one of the first such fill up a I had 18.8 and got nervous afterwards that I was so close to empty. Since then I've realized there may be as much as 22+ gallons in the tank total.

I've been just filling up to the first auto stop also, for consistency.

I figured I'd tweak that value if data suggested so. I was careful to watch the last tank the moment it hit 0 miles remaining so I could capture the total miles in the tank accurately

Mark P

Thanks. I do think I've seen >600 after a fillup, but that was before I adjusted the accuracy so maybe that did help some.

MP4.2+6.0

on other Audi's, I have noticed a real time correction to estimated miles to empty. Saw that with my C5 and D3 where done with VAG COM, and even back on my 85 5000 where it was a standalone module with dip switches. You can verify just by looking at "before" and "after" miles to empty display if you change the correction factor at any point.

Mark P

Could be. The only time I tweaked it was while at the pump after fillup, and I didn't pay attention to before/after, as it just changed after fillup

Mark P

Update: I updated data after completing tank#11 in a newer post:
https://www.audiworld.com/forums/sho...php?p=24520317