Average MPG

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SciroccoCW
Posts: 270
Joined: Fri Aug 11, 2017 1:18 pm
I drive a: 1.4 TSI 122/125
In: Oryx White
With a: Manual box
Options: 2015MY, Bi-Xenon, 18" Interlagos, Start/Stop, Bluetooth, Sat Nav, Panoramic Roof, Parking Sensors, Heated Seats, Interior LED's, Projector Puddle Lights, Mudflaps, Winter Pack, Rubber Mats, Stainless Steel Pedals, VCDS Tweaks
Location: Hertfordshire - UK

Average MPG

Post by SciroccoCW »

I was averaging 38-40 MPG according to the MFD. Now for some reason its dropped down to 31-32.. I havent really changed my driving style. Any ideas?
blower
Posts: 466
Joined: Tue Oct 06, 2015 7:01 pm
I drive a: 1.4 TSI 160
In: Reflex Silver
With a: DSG box

Re: Average MPG

Post by blower »

Common factors that affect MPG that most people don't realise:

-Wet weather, increased rolling resistance can drop MPG as much as 10%
-Cold weather - MPG tends to go down in the winter, this is especially applicable if you do a lot of short journeys (driving for less than 15-20 minutes)
-Change of journeys to those with even moderate inclines: this has a big impact on the MPG of a petrol engine (less so a diesel)

If you are doing the same sort of journeys, are aware of a drop in MPG in cold / wet weather, are using the same fuel, haven't recently changed your tyres, have checked your tyre pressures, are not carrying more passengers than usual........then maybe something is wrong.

Blowers nuggets of useful information:

A warm engine is not when your coolant temperature reads 90C, a warm engine is when your oil is at least above 60c

A small petrol engines gets a large proportion of its mpg efficiency from being able to coast with less losses than a diesel, this is because they are lighter and the cylinder displacement / size is usually less (less friction).
The moment you start adding external resistance (weight/passengers, hill inclines, tyre rolling resistance via weather or tyre pressure) and hence having to make the engine work - the overall mpg goes down by a far greater percentage than a diesel.
The result is external factors have a far bigger impact on MPG with a small displacement petrol, than someone who has had a diesel in the past may be used to.
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SciroccoCW
Posts: 270
Joined: Fri Aug 11, 2017 1:18 pm
I drive a: 1.4 TSI 122/125
In: Oryx White
With a: Manual box
Options: 2015MY, Bi-Xenon, 18" Interlagos, Start/Stop, Bluetooth, Sat Nav, Panoramic Roof, Parking Sensors, Heated Seats, Interior LED's, Projector Puddle Lights, Mudflaps, Winter Pack, Rubber Mats, Stainless Steel Pedals, VCDS Tweaks
Location: Hertfordshire - UK

Re: Average MPG

Post by SciroccoCW »

One thing that did happen was that I managed to let my petrol run out entirely by accident. Not sure if that would affect the figures, but after driving normally for over a week I'm still stuck at 31-32 mpg. It is a lot colder now with frosty mornings and I do only drive about 15 mins to work each morning through country lanes. I'm using shell Vpower, tyre pressure is all fine and it's just me driving the car.
Cuprabob
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I drive a: GT 2.0 TDI 170/184
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Location: S/W Scotland

Re: Average MPG

Post by Cuprabob »

You haven't by any chance swapped over from long term average display to short term journey average display, have you.

Long term has a "2" displayed on the top right of the MFD. Short term has a "1" displayed on the top right of the MFD.

Short term memory resets after the ignition is switched off for roughly 2 hours.
Long term only resets when it is manually reset or distance reaches 9999miles or time elapsed reaches 99h 59m
User avatar
SciroccoCW
Posts: 270
Joined: Fri Aug 11, 2017 1:18 pm
I drive a: 1.4 TSI 122/125
In: Oryx White
With a: Manual box
Options: 2015MY, Bi-Xenon, 18" Interlagos, Start/Stop, Bluetooth, Sat Nav, Panoramic Roof, Parking Sensors, Heated Seats, Interior LED's, Projector Puddle Lights, Mudflaps, Winter Pack, Rubber Mats, Stainless Steel Pedals, VCDS Tweaks
Location: Hertfordshire - UK

Re: Average MPG

Post by SciroccoCW »

No it's definitely on long term
Cuprabob
Posts: 5014
Joined: Sat Aug 07, 2010 2:31 pm
I drive a: GT 2.0 TDI 170/184
In: Rising Blue
With a: Manual box
Options: Panoramic Roof, 19" Black Luganos, Vienna Leather, Parking Sensors, DAB, Dynaudio, Bluetooth, Cruise, Folding Mirrors, Xenons
Location: S/W Scotland

Re: Average MPG

Post by Cuprabob »

Check the distance and elapsed time to see if it's reset recently. By the nature of how the average is calculated the value can vary a fair bit at the start just after a reset and stabilise over time /miles.

It's also worth comparing it to the short term journey average which is actually a more representative figure if you are trying to identify any change.
Billc
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Joined: Sat Oct 23, 2010 8:01 am
I drive a: R-Line
In: Ultra Violet
With a: DSG box
Options: Dynaudio, DCC, bi-xenons

Re: Average MPG

Post by Billc »

Or rule out issues with the MFD completely and do a manual brim-to-brim test and see how many miles you get out of a full tank. It'll be different to what the MFD says every time because the MFD's are typically optimistic but you'll get a real figure instead. Mine is 7% optimistic on mpg - I record mileage every time I fill the tank and get a manual figure which then gives me a long term average.
Bill in Norfants
User avatar
SciroccoCW
Posts: 270
Joined: Fri Aug 11, 2017 1:18 pm
I drive a: 1.4 TSI 122/125
In: Oryx White
With a: Manual box
Options: 2015MY, Bi-Xenon, 18" Interlagos, Start/Stop, Bluetooth, Sat Nav, Panoramic Roof, Parking Sensors, Heated Seats, Interior LED's, Projector Puddle Lights, Mudflaps, Winter Pack, Rubber Mats, Stainless Steel Pedals, VCDS Tweaks
Location: Hertfordshire - UK

Re: Average MPG

Post by SciroccoCW »

I haven't done a manual test. But I drove up north to stoke-on-tent which is about 2.5 hours away the other day. The round trip has left my Long-term Average MPG at 34.4 which is still better but a significant drop from 38-40. But then wouldn't it slowly drop from 34.4 back down to 31 if my normal daily drives equates to that??

In a 1.4 125ps petrol I would have expected my average MPG to be higher, though like I said before I drive to work in the morning through country lanes for 15 mins, then the same home and then I go in town where its mostly roundabouts and traffic lights so a lot of starting and stopping.
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