How accurate is your trip computer's MPG?

[ibiza lad]

I've got a 08 plate Ibiza FR TDI. I've now done nearly 7000 miles in mine. The one thing I’ve noticed is how inaccurate the trip computer’s MPG reading is. I've average about 46mpg over the 7000 miles. That is measuring all of the fuel I have put in the car. [Yes I know I am sad, I keep a log book of fuel]. The overall average [2] reads about 57mpg. So that is way off.

The trip average [1] is also way off. As an experiment I did a 200 mile motorway trip with the cruise control set to about 55 mph, in sixth gear. So I was doing about 1700rpm give or take. The trip computer suggested a magical 75mpg, in reality I’d used about 15 litres of fuel which works out at about 60mpg.

So both are way off! I was just wondering is this typical of the VAG trip computer or should I raise this with the dealer at the next service? Or does the way you drive affect the accuracy?

 

[st10587]

i had mine read 80 odd mpg on one trip

where abouts in guildford you from i should keep a eye out for ya!

 

[ciano125]

Yep, they're miles out. I've done 10k miles in my 07 reg FR TDi and overall it is averaging low 40s, the trip (2) says high 50's. It even said 90mpg on the way into work last week. I cant get more than about 520 miles to a tankful (about 50 litres).

 

[ibiza lad]

i had mine read 80 odd mpg on one trip

where abouts in guildford you from i should keep a eye out for ya!

to the north west in Knaphill, or Knaffhill if you like!

 

[st10587]

to the north west in Knaphill, or Knaffhill if you like!

cool!! im always floating around the guildford/woking area either shopping or passing through!

 

[Nath.]

Yeah the petrol FR's read the other way, It says 33mpg but it's more like 38 when you do the math's

 

[fatcatman]

I hate these threads because everyone gets much better mpg than me!

Before re-map I got 56-7mpg at best on the trip, 42-44mpg real life and after re-map I get 45mpg at best on the trip and 39-40 mpg in real life.

Car is a 'facelift' FR Tdi

 

[nealo]

I've calculated my mileage over the last 4 tanks' worth of shell v-power diesel and the trip computer is only +0.2% out!

 

[diss_50]

****...

 

[2 Many Ibiza's]

My 2007 Petrol FR over reads. The gauge says i average 40mpg but im actually only getting 36mpg

 

[TazB]

to every 1... whats your exact method of calculating the real mpg? i've never done it.

 

[Disco_Biscuit]

to every 1... whats your exact method of calculating the real mpg? i've never done it.

Fill to the brim, reset trip meter, run till empty, refill, see how many litre's it has taken to fill up,

ie: 33 ltrs 350 miles

to make life easier use this http://www.guycroft.clara.net/utils/mpg.html

 

[markthommo_84]

I worked mine out a few tanks ago. I always reset the [2] bit when i fill up, i did 440 miles before refilling again, and it took 40 litres to fill, which i work out to be 49.94 mpg, the trip computer said 50.0

I can live with that! i have read most of the diesels over estimate. i think it depends on how you drive, how far, etc. obviously the longer journeys get a more accurate average - more data to calculate.



TazB :
calculating MPG - miles divided by litres X by 4.54.

440 miles to 40 litres.... 440/40, times by 4.54 = 49.94


or, use: http://www.torquecars.com/tools/uk-mpg-calculator.php

it remembers your last 4 entries, gives an average mpg over your last 4 tanks, and gives you a cost per mile. mine's 9 pence. fuel cost only obviously.

 

[Clone]

I've only once done over 400miles to a tank and that was almost constant motorway driving going down south - then again i don't fill it up often. I'm going to now though!

 

[TazB]

ach i only put 20 quid in at a time unless i know im gonna go far.

so when you fill to the brim are you venting aswell? cos when venting it depends on how much patience i've got, how much i can squeeze into the tank

 

[luna fr]

ach i only put 20 quid in at a time unless i know im gonna go far.

so when you fill to the brim are you venting aswell? cos when venting it depends on how much patience i've got, how much i can squeeze into the tank

It doesn't matter if you vent or not as long as you fill up the same way both times, I fill up every two weeks and I have checked a couple of times the MPG vs Computer and it seems to over read by about 2MPG. Its a pre-facelift fr Tdi.