103TDI Range display

[Corey_R]

My question is, if cars 'read fast' , i.e. 100km/h may read 105, does this translate to odometer and trip computer error also?
If so, this would explain it - the odometer says you've travelled 105 km's when in fact you've only done 100 - an instant 5% hit on the calculated fuel consumption..

No, the odometer should be reading 100% accurate, even when the speedo is reading (usually for VW) 7% slower. I have noticed that with my Polo GTI it usually ends up coming in around 7.9L/100km for the tank of fuel based on the trip metre, but based on the petrol bowser I'm usually getting 8.2L/100km

Oddly enough, my MKV Golf GTI was completely accurate - trip metre vs bowser.

[hoi polloi]

Bear in mind also that when doing manual calculations the bowsers themselves are not 100% accurate - this may induce an error as well...

Regards,
- Anthony.

[logger]

True - I was able to fit what the bowser said was 55 litres into my 55 litre tank a couple of weeks back with no difficulty. No surge/overflow. Must have been running on vapors when I drove it in. So either the bowser slightly overread or my tank readily fits more than specified. Having said this the bowsers should average out in the long run. Another variable is the point at which you decide it is full on any given occasion may vary. Will average out as well I suspect. As Coreying said odo should be accurate though.

[Corey_R]

Yeah - bowsers obviously also change depending on the weather (hot / cold temps cause the fuel to expand and contract)

[NovaArtist]

Filled up a 5 litre jerry can for the lawnmower up at the local BP (and when the bowser read 5L, there was still about a 500mL gap before the 5L mark was reached. You really have to wonder sometimes - as this simply means you are paying 10% more for your fuel. I told them their pump was out - but they just shrugged - They don't care. If you fill up at 1.25 per litre - but are actually paying 1.37 due to the pump being out - I imagine you would not be impressed. I don't know how often the government checks the pumps for accuracy - but I would suggest they need to do it more often.

[Corey_R]

As I said - the main problem is fuel expansion / contraction with hot and cold weather. Petrol companies don't care in Australia because the expansion means THEY come out in front. It's only in countries which are always cold where the contraction would mean the motorist always comes out in front where the petrol companies can be bothered making a browser which takes that into account.

[logger]

Yeah - bowsers obviously also change depending on the weather (hot / cold temps cause the fuel to expand and contract)

Disagree on that one coreying. It depends on how the bowsers actually measure fuel. If they measure volume, which I suspect they do, then the volume of fuel you get (in litres) will not vary with temperature.
What will vary with temp is the calorific value of the same volume of fuel. So theoretically 50 litres of cold dense fuel will give you more bang for your buck that 50 litres of hot expanded fuel. It both cases you ARE still getting the exact same volume of fuel. You are getting what you paid for.
A more sophisticated system would sell you fuel by weight which more accurately reflects the amount of energy for a given quantity regardless of temperature. Having said all this if the temp was a signifigant issue on car size tanks of fuel which I doubt, one can imaging the mileage testers putting in super cool fuel to maximise range which I doubt they actually do.

[hoi polloi]

A more sophisticated system would sell you fuel by weight which more accurately reflects the amount of energy for a given quantity regardless of temperature.

Which is actually what the fuel quantity indicators on complex aircraft read... The transmitter is a number of capacitance probes in each tank rather than a simple float system.

Regards,
- Anthony.

[logger]

Which is actually what the fuel quantity indicators on complex aircraft read... The transmitter is a number of capacitance probes in each tank rather than a simple float system...

...and the capacitance probes typically only form part of the aircraft system. You will find there is also a radiation attenuation densitometer which calculates the density of the fuel, applies this to the levels reported by the capacitance system to derive a fuel weight. Ironically, even with aircraft, the fuel company still meter and fill by volume, whilst the pilots use it by w8.

[Mk6 Golf]

My highest (so far) is 960 km

I filled up the fuel tank on Sunday and was pleasantly surprised to see my MFD informing me I have a range of 1030km. Nice!

I've had my new Golf (103TDI) for a few weeks. The highest I've had so far is 960 km. At first I was wondering why it was different when I filled it up (I've done some long drives since I had it and some city driving) as I assumed it would be the same each time, but then I found out that the current 'range' is calculated based on various factors, such as your past (recent) average consumption rates.

btw - This is the first car I've owned with a range display and I'm loving it, along with all the other great Golf features.

[Corey_R]

Disagree on that one coreying. It depends on how the bowsers actually measure fuel. If they measure volume, which I suspect they do, then the volume of fuel you get (in litres) will not vary with temperature.
What will vary with temp is the calorific value of the same volume of fuel. So theoretically 50 litres of cold dense fuel will give you more bang for your buck that 50 litres of hot expanded fuel. It both cases you ARE still getting the exact same volume of fuel. You are getting what you paid for.
A more sophisticated system would sell you fuel by weight which more accurately reflects the amount of energy for a given quantity regardless of temperature. Having said all this if the temp was a signifigant issue on car size tanks of fuel which I doubt, one can imaging the mileage testers putting in super cool fuel to maximise range which I doubt they actually do.

Check out ACA and Today Tonight who both did stories on this in the past. They specifically compared various pumps in Australia, measuring out exactly 5L. Then back in the lab had 'petroleum experts' re-measured the fuel again to show how much the fuel had 'shrunk' by. They then contrasted that to Canada where all the bowsers are fitted differently so that they measure the fuel differently, since the temps are much colder there the customer would always be winning.

Anyway - I'm not going to get into a big argument over this or anything - because I'm simply relying on the information from petroleum experts and from current affairs programs. I personally have no scientific expertise in the area, nor could I be bothered doing any real life experiments of my own - cause well, it makes no different in the end. We're not going to change the way Petrol companies do business even if the experts and the current affairs programs are correct.

[hoi polloi]

You will find there is also a radiation attenuation densitometer which calculates the density of the fuel, applies this to the levels reported by the capacitance system to derive a fuel weight. Ironically, even with aircraft, the fuel company still meter and fill by volume, whilst the pilots use it by w8.

Yeah, I deliberately tried to simplify it a bit (being a car forum, not an aircraft one)...

Radiation desitometers are certainly used in some systems, but by the time I left the industry they'd well and truly moved on and found better methods of calculating density (without the use of radioactivity)... I'd be surprised if there were any newly designed systems using these - plenty of legacy installations out there (Boeing 767 etc. etc.)

As an aside, XD and XE Falcons use a capacitance type sender...

Regards,
- Anthony.

[Mk6 Golf]

A bit 'off topic'

Maybe discussions about 'fuel expansion / contraction with hot and cold weather' or 'petroleum experts' etc.. is getting a bit off topic, IMO.

[Highlander]

Temperature and Volume = The Laws of Physics

Disagree on that one coreying. It depends on how the bowsers actually measure fuel. If they measure volume, which I suspect they do, then the volume of fuel you get (in litres) will not vary with temperature.
What will vary with temp is the calorific value of the same volume of fuel. So theoretically 50 litres of cold dense fuel will give you more bang for your buck that 50 litres of hot expanded fuel. It both cases you ARE still getting the exact same volume of fuel. You are getting what you paid for.
A more sophisticated system would sell you fuel by weight which more accurately reflects the amount of energy for a given quantity regardless of temperature. Having said all this if the temp was a signifigant issue on car size tanks of fuel which I doubt, one can imaging the mileage testers putting in super cool fuel to maximise range which I doubt they actually do.

We can't deny the laws of physics. ALL liquids expand when heated and contract when cooled.

For the purpose of fuel measurement there is an Australian standard which is set at 15 degrees celsius. There are regulations and procedures for volume corrections.

Here is one link for example

https://www.ocba.sa.gov.au/assets/files/volume.pdf

Sorry to spoil a good argument. You even refer to hot expanded fuel and cold dense fuel, in your statement, apparently interchanging volume and mass. Some merit there though as wouldn't hot fuel be less dense as density is defined as mass divided by volume. Mass the same, volume greater at higher temperature resulting in lower density.

[Corey_R]

Maybe discussions about 'fuel expansion / contraction with hot and cold weather' or 'petroleum experts' etc.. is getting a bit off topic, IMO.

Maybe - that's why I said I'm gonna leave the topic, because it's really beyond the scientific knowledge of myself. But in reality - if the experts are correct - it could actually be very ON topic - as it may explain the discrepency between the bowser and the trip metre