Why such a difference in MPG from my A4 and wife's A3 Sportsback

[SRRAE]

About 3 months ago I got an A4 Technik, enticed by the low tax, potential good mpg and I wanted parking sensors front and rear so my wife had no excuse for hitting posts if she borrows my car again.

My wife recently got an Audi A3 2.0tdi sportsback, because her then Mazda 3 didn't have side sensors and she ripped half the passenger side of the car pulling out of a driveway with VERY large wall.

Her A3 is £30 a year tax and looking at the engine spec is nearly identical to the one in my A4.

However, today I drove her car to work instead of mine, and the onboard computer reported 57mpg where the A4 Imlucky to get 44mpg. The trip is about 20 miles in total with the first, around 5 miles, slow town dropping 2 kids off at schools and then its motorway and dual carriageway for the rest where I sit at 60mph.

I don't understand why her A3 is doing nearly 30% more mpg where the engine is practically the same, feels faster and the weight difference between the 2 isn't 30% more surely

 

[JRock247]

I'm certainly no expert but will add my comments.

Weight will definitely have an effect on the MPG between the cars, not necessarily the 30% difference you are seeing but will certainly be different between the cars. Different gearboxes will also affect the MPG (manual Vs auto - CVT/S-Tronic)

What is the age of each car, new cars tend to need time to 'settle in' before they give a more accurate/consistent MPG reading.

Tyres can even have an affect on the MPG, so it could just be a combination of all the subtle differences between the cars that add up to 30%, although I would not expect that much of a difference.

Perhaps one of the vehicles is not running correctly??? Do you know if either vehicle was affected by the emissions issue. When mine went in for the 'fix', I did notice a drop in MPG although Audi saying it will make no difference!

 

[jdp1962]

In both cases, how are you measuring the fuel consumption? Are you taking mpg figures from the DIS or doing an exact calculation based on mileage covered divided by the number of gallons put into the tank to brim to the same point?