Probably a really stupid question about the DIS MPG reading...

[mookie]

This is probably a really dumb question, but I did search and couldn't find an answer.

On my DIS (1.9tdi), I get a nice useful reading for the remaining range from fuel in the tank, and the overall average MPG (the O with a line through it) also. However the realtime MPG reading is nigh on useless - if you have a steady acceleration you can get it to give a useful number, but almost any other situation and it's pinging from 30mpg to 170mpg and everything in between, usually flapping about in the 90s and early 100s before showing mid50s for a bit! Is this how it should work? I can't believe that's what it should be doing.... I'd expected (after reading the manual) to see it go up and down within a more realistic range (high 30s to low 50's) depending on my recent acceleration and recent speed?

I have my flame retardent suit on, and my most sturdy crash helmet at the ready for the replies I might get. However I'm coming from a driving history involving Mk2 Golfs and Corrados and so technology like this is blowing my mind...

 

[quattrojames]

The instant MPG is exactly that, the reading at that moment in time.

Underneath the stalk is a button, have you seen that? That will flick between the two DIS memories, and the third press blanks the screen. Memory 1 gives readings over the duration of the journey, but resets when the car is stopped for more than two hours. Memory 2 gives a cumulative total and isn't reset.

So, memory 2 will give you your all time average mpg. Memory 1 will give you the mpg of the journey you're currently undertaking.

 

[Artimus]

I've found with previous cars that the "Instant" readout is relatively useless unless you're sitting still with the engine idling, as it fluctuates wildly depending on speed\throttle\incline\air density\etc. If you try to keep the figure steady, you'll never accelerate. It's best use is to inform you of what roads\traffic\driving style have what effect on your mpg. So best to forget it's there and stick with the "average" setting.

 

[stu_m]

The thing is when your driving most of the time your constantly adjusting the throttle without even knowing about it

Have you got cruise? If so put it on and the readout will be almost constant till you have to speed up or slow!

 

[mookie]

Yeah that's my point, what is the use of it?! I had a delayed realtime MPG readout on my Mk2 that was better than this, updated every 30seconds or something. At one point driving home tonight it was stuck on 200mpg before going -----mpg as it presumably went too high to register any more ha ha ha

 

[stu_m]

Just ignore it simple!

Do tank to tank mpg its the only way its accurate

 

[mookie]

I've never not done full tank mpg, but like to be nerdy and see what I'm up to there and then.

 

[stu_m]

You don't have to do full tank to empty just fill it up drive a few hundred miles then fill it up again and work it out off that it will probably be about right

The dis is usually out anyway

 

[Artimus]

I've never not done full tank mpg, but like to be nerdy and see what I'm up to there and then.

Reset the temporary trip [1] at the start of each journey, then it pretty much updates instantly, for the first few miles at least.

 

[PetrolDave]

At one point driving home tonight it was stuck on 200mpg before going -----mpg as it presumably went too high to register any more ha ha ha

It shows ---mpg when your foot is off the throttle and the engine rpm is over about 1200rpm - because then there is no fuel being injected at all.

The instantaneous mpg is averaged over the last few seconds (5 or so) only, so it's always going to vary wildly.

 

[mookie]

You don't have to do full tank to empty just fill it up drive a few hundred miles then fill it up again and work it out off that it will probably be about right

The dis is usually out anyway

You're preaching to the faithful there mate. For my last car, Corrado VR6, I had an Excel spreadsheet with every single fuel stop (£10-80) on it, with tables, line graphs... the lot! Lifetime mpg of that car in my ownership was 26.1mpg, I have the graphs to prove it ha ha ha ha

 

[mookie]

It shows ---mpg when your foot is off the throttle and the engine rpm is over about 1200rpm - because then there is no fuel being injected at all.

The instantaneous mpg is averaged over the last few seconds (5 or so) only, so it's always going to vary wildly.

According to the manual it's every 30metres, I wish it was much larger than that.

 

[stu_m]

You're preaching to the faithful there mate. For my last car, Corrado VR6, I had an Excel spreadsheet with every single fuel stop (£10-80) on it, with tables, line graphs... the lot! Lifetime mpg of that car in my ownership was 26.1mpg, I have the graphs to prove it ha ha ha ha

I do it the easy way! I have an app on my phone that does the hard work for me I brim it once its empty usually every 3-4 weeks stick the fuel amount, cost and miles in to the app and it just records it

I have also adjusted the consumption with VCDS and it now reads 0.2 mpg out