Fuel Gauge Calibration?

[bigjohn]

I've never really managed to get much more than 50 litres into my mkII even though it's a 60 litre tank. It might be because I stop at the first click but I suspect there is a fair bit of petrol left when my on board computer shows you have near zero miles left. Is there a procedure to check calibration?

 

I can't complain too much as this gives me a 500+ miles range but I really miss the 700+ mile range of my old 1.9pd Superb mkI. 

 

This issue has resurfaced as I'm on a many 100's of miles UK holiday during a fuel crisis!!!  I used to love getting off the ferry in Zeebrugge knowing I could get to my destination without ever having to think of filling up!

[chimaera]

The B5 had a bigger tank (62 vs 60 l). I suspect the reserve point is set at a higher volume too. I think the biggest fillup I've ever done on mine is around 55 l and the MFD was showing less than 20 km remaining. I have corrected the MFD fuel consumption factor so it reads true as well. It looks like it makes sure there is still a bit left in the tank when the gauge hits zero.

 

It's also not clear how much of the tank volume is available for fuel, or how tank volume is determined/specified.

[bigjohn]

I certainly got the full 62l into the mk1 - if not a bit more! and it was a little bit more economical compared to the petrol - almost always got 50mpg out of the mkI but get 45+mpg out of the petrol mkII sometimes approaching 50mpg on a good run.

 

 

[vborovic]

On 27/09/2021 at 23:18, bigjohn said:

I can't complain too much as this gives me a 500+ miles range

 

The actual tank capacity is 54 litres on the Mk2 ... On another note, I'm happy If I manage to squeeze 500 kms out of mine (bit of a heavy drinker the car) ... 😅

[chimaera]

Quote

The fuel tank has a capacity of about 60 litres, containing a reserve of 10.5 litres.

From the owner's manual.

 

[vborovic]

14 minutes ago, chimaera said:

From the owner's manual.

 

 

Maybe on paper, I've had the car on 0 miles remaining, fuel needle fully down, wondering if the car would even start or die of fuel starvation, and it could never accept more than 54 liters (maybe .20-.30 +, at most). I don't know where the missing " 6 liters" are in that case ...

[chimaera]

6 minutes ago, vborovic said:

 

Maybe on paper, I've had the car on 0 miles remaining, fuel needle fully down, wondering if the car would even start or die of fuel starvation, and it could never accept more than 54 liters (maybe .20-.30 +, at most). I don't know where the missing " 6 liters" are in that case ...

That's what we established further up the thread. The car tells you it's empty when there are 8-9 l left in the tank.

[26DIPP]

You just need to be brave and patient when the fuel light comes on and keep going.

 

[bigjohn]

6 hours ago, vborovic said:

 

. On another note, I'm happy If I manage to squeeze 500 kms out of mine (bit of a heavy drinker the car) ... 😅

 

I'd be happy with that with the lovely v6. When I bought mine price / economy was important as it was to be pressed into service on a long commute and pre dieselgate it was way cheaper by many £1000's to buy the petrol compared to the diesel. I calculated that the price difference v petrol mpg would take 15 years to equalise and by then it'd be well past the scrap stage. What I didn't factor on was how economical the 1.4tsi was going to be in real life - way better than my original sums. 

 

Courtesy of Covid my long commute is no more - v6 could be a consideration now!

 

[bigjohn]

3 hours ago, vborovic said:

 

Maybe on paper, I've had the car on 0 miles remaining, fuel needle fully down, wondering if the car would even start or die of fuel starvation, and it could never accept more than 54 liters (maybe .20-.30 +, at most). I don't know where the missing " 6 liters" are in that case ...

 

Hence my original question. I was wondering if there was a way of re-calibrating with VCDS etc?

 

I've noticed the mkIII seems way better re "real life" capacity

Edited 2 October, 2021 by bigjohn

[vborovic]

8 minutes ago, 26DIPP said:

You just need to be brave and patient when the fuel light comes on and keep going.

 

 In any case, I'm less stressed while driving a car with a proper fuel tank, compared to a car with only the batteries, since you can't just sip extra electricity from a jerry can ... 🤣

[vborovic]

5 minutes ago, bigjohn said:

I was wondering if there was a way of re-calibrating with VCDS etc?

 

From the top off my head, I think there is an offset option that goes both ways, something like -10 to + 10 litres ... to be used with extreme caution of course.

[J.R.]

Calibration is done with a full tank and the factory calibration of every vehicle I have had has been spot on as is the range that is shown when full based on previous journeys.

 

It remains spot on at 3/4 & 1/2 a tank but a correction comes gradually into play between 1/4 of a tank and when the low fuel light comes on, it basically "loses" 7 litres or so to create a "virtual" reserve capacity, most of us will have noticed that the last 1/4 of a tank seems to be consumed very quickly and the remaining miles evaporate before our eyes.

 

I always drive 60 miles after the guage shows empty and zero miles remaining although with this Common Rail injection system I don't push the limits and risk running out, on all of the previous cars I would carry a jerrycan on the first tankfull and drive it till it ran out to see the real range.

 

When it had run out I refilled exactly 5 liters from a jerrycan and given it would only have been an inch at best across the wide tank bottom I was amazed to see the fuel guage move to the equivalent of 5 litres and to see that I had 40 miles range, I drove less than 2 miles to the filing station during which time the range dropped to 30, then 20, then 10 then zero miles, the "virtual reserve" algorithm was working overtime.

 

A long posting but the message from me is do not try to make adjustments with VCDS without first fully understanding how accurate the fuel sender actually is and how the virtual reserve works, all you will achieve is to have incorrect readings across the whole of the tank range and the cheating that goes on robbing you of 7 liters and 50 - 100 miles range below 1/4 tank level will still happen.

[bigjohn]

Funnily enough I drove up from Somerset to Yorkshire today, I don't know whether it was the awful weather or I had half an eye on on the fuel crisis and was driving slower than usual and my overall range combining miles done and range left in the tank crept up to 600 miles  - it's normally in the 500's. Not bad but I still miss the 750mile range I could get out of my mk I Superb. Still cant put much more than 50l into it though.

Edited 2 October, 2021 by bigjohn

[chimaera]

On older cars there was a correction procedure for the reserve limit but I have not seen anything similar documented for our cars.

 

It involved draining the tank and refilling it with exactly 9 l of fuel then using an adaptation channel in the instruments to position the needle at the top of the red zone on the fuel gauge.