Hi, just a quick question

how much over, are the average mpg fuel readings on the octavias dash displays, I know you can brim fill tank etc etc, but just interested in how much over the reading is on average.  ( I’m assuming you get less than what is says) or are they fairly accurate.

Around town my display is 38- 40mpg

Edited 12 March, 20188 yr by andyasjl

I'd imagine it might differ somewhat car to car. Mine seems pretty accurate though, usually within about 0.5mpg compared to brim calculated figures.

My real tank to tank mpg seems to be around 90% the reading from dash display. So a long run on trunk roads may give a dash reading of 68mpg which equates to a true tank to tank figure of 62mpg.

Thanks, I was guessing around 10% difference, just been out in the car and found my long term reading is 42.5 had car 6 months and I’ve never reset it, I better slow down a bit...

Long term resets automatically after 99 hours or 9999 miles/km.

1 hour ago, Gerrycan said:

Long term resets automatically after 99 hours or 9999 miles/km.

Oh cheers, leant something new, again....

10 hours ago, Gerrycan said:

Long term resets automatically after 99 hours or 9999 miles/km.

Or after battery removal/replacement

I have the feeling it will also do it after a tyre set change. Not 100% sure but I think it was automatic....

 

 - Bret

I have found the average dépends greatly on your driving style.

I have a pretty constant driving profile 95% on the highway, cruising at 120kph & find the average fuel on the maxidot almost perfect.

 

However, if you mix driving profiles e.g. over Xmas I had 2 weeks with many short journeys to the tip & DIY stores the calculated average at my next tanking was around 10% out.

Ok cheers guys

18 hours ago, Gerrycan said:

Long term resets automatically after 99 hours or 9999 miles/km.

Yeah my VRS245 just reset for second time today 7200 miles, 200 hours driving at an average speed of 36 mph. Maxidot seems very accurate compared to brim to brim checks, probably only 1% out.

200 hundred hours reset must be an update from my 2014 model's 100 hours.

Makes a lot more sense though as I would probably have to break several speed laws to enable a distance reset even with just kilometres setting.

 

I'd have thought it should be pretty accurate nowadays given stop/start and the fact that cars have known how much they're using for a long time.

I've long had a theory that the inaccuracy was when stationary, the car cannot calculate MPG when you're doing 0 miles but using fuel. Like the whole "cannot divide by zero" maths rule, if one of the inputs for its calculations is zero, it assumes the answer is zero. Stop start should help make it more accurate as you're not using anything when stationary (if you have it activated).

On ‎13‎/‎03‎/‎2018 at 18:25, brettikivi said:

I have the feeling it will also do it after a tyre set change. Not 100% sure but I think it was automatic....

 

 - Bret

Nope, had new tyres fitted today and long term distance was unchanged.

I did need new tyres it was not just to test the hypothesis  

22 minutes ago, Robbijay said:

I'd have thought it should be pretty accurate nowadays given stop/start and the fact that cars have known how much they're using for a long time.

I've long had a theory that the inaccuracy was when stationary, the car cannot calculate MPG when you're doing 0 miles but using fuel. Like the whole "cannot divide by zero" maths rule, if one of the inputs for its calculations is zero, it assumes the answer is zero. Stop start should help make it more accurate as you're not using anything when stationary (if you have it activated).

The can't divide by zero thing is just because you adopt the MPG display, if you elect to have L/100 then when the car is stationary but engine running (stop/start disabled) the instant consumption converts to L/hour. So the system knows how much fuel is being consumed. 

I think it even takes into the account the consumption of the Nordic engine pre-heating systems (Webasto).

Edited 14 March, 20188 yr by Gerrycan

My display is consistantly optimistic by 0.3L/100km below real consumption. (1.8 tsi dsg)

30 minutes ago, Woland said:

My display is consistantly optimistic by 0.3L/100km below real consumption. (1.8 tsi dsg)

Every car is slightly different but at least yours is consistent and easy to work out the real figure. 

I believe that you can adjust the display accuracy with VCDS if it really bothers you. 

 

On 14/03/2018 at 12:37, Robbijay said:

I've long had a theory that the inaccuracy was when stationary, the car cannot calculate MPG when you're doing 0 miles but using fuel. Like the whole "cannot divide by zero" maths rule, if one of the inputs for its calculations is zero, it assumes the answer is zero. Stop start should help make it more accurate as you're not using anything when stationary (if you have it activated).

The divide by zero happens for the instantaneous MPG calculation while engine braking so no fuel is being used.

It shouldn't be a problem for the average calculation because it should simply divide distance travelled by fuel consumed since the figures were last reset.

On 14/03/2018 at 12:56, Gerrycan said:

The can't divide by zero thing is just because you adopt the MPG display, if you elect to have L/100 then when the car is stationary but engine running (stop/start disabled) the instant consumption converts to L/hour. So the system knows how much fuel is being consumed.

There's no reason why it couldn't display hours per gallon while stationary.

1 hour ago, Rodge said:

 

There's no reason why it couldn't display hours per gallon while stationary.

I think my wife's Fiesta switches to gallons/HR when stationery. With stop start technology it is probably not necessary show this figure.

My car does not have stop/start and shows 0.4 to 0.5L/hour on tickover, warmed with no ancillaries running.

To be useful in gallons per hour you would need two decimal places of accuracy.