DIS MPG accuracy.

Birchall

Dick Chown Award 2016
I have heard people comment about the innacuracy of the DIS average MPG figures.

I have been checking mine over the last three months and I have found it to be very accurate.

My check is using the “full to full” method.

I fill the tank each time to the full capacity ensuring that I let the fuel settle for a few seconds and then fill again until it auto shuts off.

I check the trip meter and therefore have a reasonable idea of the true MPG.
Then I zero the trip and do the calculation at home.
Importantly I also zero the average MPG on the DIS so that it is measuring this tank and not including previous journeys.

One thing that that helps my accuracy is that I run slightly larger diameter tyres and this happens to compensate for the 3% or so over-read of the speedo.

So I am quite impressed. Over 10 fills it has been spot on each time!!!!

One thing that is innacurate (or should I say optimistic) is the range at the fill up.
It becomes more accurate as the tank empties but it seems to indicate a range that would leave the tank bone dry.

Steve B
 
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Not sure why that would be?

Perhaps I am just lucky?

it shouldn’t be due to the tyre sizes because they influence the kilometre and the speedo by the same percentage??

Mine is accurate to within 1 MPG every time?

Perhaps they tweaked something on 2004 cars onwards?? unlikely I guess.

Steve B
 
Hi Steve
On AMF 3/2002 car mpg optimistic by about 6mpg, range optimistic by roughly 150miles on fill-up; and yes as you more accurate with lower fuel level.
On ATL 5/04 mpg pessimistic by about 3mpg but range is accurate.
I always felt that the 02 car with the small tank may have had the software/hardware for the large tank :confused:
Martin
 
Using Steves methods i'm agreeing with Steve, the potential on a full tank can seam a bit optimistic but i'm thinking that it might be something set in the factory?..... driving in optimum conditions,ie a flat road and no stop start running and running at a constant 65 - 70mph. I don't know just guessing. However I think we got fairly close with the fuel range potential with our 514 miles on a brimmed tank (1.4 BBY petrol) to as empty as i dare take it.

The dis readout follows what your doing. You can start a journey with say 235 miles left in the tank, then go into economy driving and after 20 carefully driven miles the range has increased to 250 left. It reacts instantaneously to how heavy or light a foot is being applied.
 
What's the difference in the capacity of the two types of tank?

I haven't done enough miles to gauge the accuracy of the DIS on mine, but just about every other VAG car I've owned up to now has been around 6-7% optimistic when it comes to fuel consumption, all on standard wheels and tyres, when compared to consumption calculated with the same brim-to-brim method as Steve B.

Reading posts on the Skoda forum (about Yetis, one of which I own) it seems that there are settings that can be tinkered with using VCDS to get the DIS (aka Maxidot in the case of the Skoda) fuel consumption?
 
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34 litres to 03, then 42 l from memory. I have never put in more than 39 l and got 649 miles from memory again - but i was really trying.
The DIS works out the range from the fuel level and the average mpg of the last 20 miles I think. When I changed the fuel filter with a full tank I lost about 3 litres (clumsy)
and the DISmpg was looking pretty poor but gradually got up to a normalish mpg by end of tank; so I think my 02 car thinks it has 42 l when it has 34 l.

514 miles is impressive on petrol, I get worried when the fuel gauge pointer is just clear off the lowest red mark and the dis has been on zero miles for 20 miles or so :eek:
Martin
 
The dis readout follows what your doing. You can start a journey with say 235 miles left in the tank, then go into economy driving and after 20 carefully driven miles the range has increased to 250 left. It reacts instantaneously to how heavy or light a foot is being applied.

Yes, sometimes when I have a long journey to do and not enough fuel to reach the destination, I drive around economically the night before and "Hey Presto" I have enough range !!!

LOL

Steve B
 
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Mine massively under reports on my TDI 90 it’s normally at least 10mpg under my fuelly app. I did an eco run over 200 Miles the DIS showed 64mpg and fuelly showed 78mpg or £13.50 for 200ish miles.
 
Mine massively under reports on my TDI 90 it’s normally at least 10mpg under my fuelly app. I did an eco run over 200 Miles the DIS showed 64mpg and fuelly showed 78mpg or £13.50 for 200ish miles.

That is strange, mine is a 90 too.

I just use an excel sheet that does the very basic calculation, not fuelly, mainly because it is a simple enough calculation

Litres to fill the tank divided by 4.546 (to convert it to gallons).
Then divide the mileage covered by that result.

Could it be perhaps[s linked to the fact that it is virtually all motorway miles?
Perhaps the system can calculate that more accurately than start stop.

I am guessing that when stationary the system has to use rough calculations of the effect on MPG, perhaps the stop start calculations are a bit more inaccurate.

That is the only thing I can think of?

Steve B
 
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I have the opposite problem with Baby Boomer, which originally over-reported by about 20% :eek: (I frankly didn't believe I was averaging 88mpg - I was correct)

However, there is an adjustment you can make with VAG-COM, where you can change it ~15% either way, with this done I am now about 5% out.

As for Project, this doesn't have a full did, so I can't tell.
 
That is strange, mine is a 90 too.

I just use an excel sheet that does the very basic calculation, not fuelly, mainly because it is a simple enough calculation

Litres to fill the tank divided by 4.546 (to convert it to gallons).
Then divide the mileage covered by that result.

Could it be perhaps[s linked to the fact that it is virtually all motorway miles?
Perhaps the system can calculate that more accurately than start stop.

I am guessing that when stationary the system has to use rough calculations of the effect on MPG, perhaps the stop start calculations are a bit more inaccurate.

That is the only thing I can think of?

Steve B

Whatever type of driving I do it’s always way under the true mpg I should be getting.


 
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