Increased fuel consumption during "running-in"

WobblyDog

I recently bought a new 1250cc Ford Fiesta (82PS version). According to my fuel consumption spreadsheet , so far I've averaged 47mpg, after 3 fill-ups and 700 miles. I'm hoping to achieve an average nearer the car's extra-urban figure of 62mpg, because in my previous car my actual average fuel consumption was about the same as its official extra-urban figure.

Is it a myth than fuel consumption is increased during running in?
If not, does anyone have any numerical data on how large the effect is?

One other possibility is that the old car's odometer overestimated distance travelled to a greater extent than the new one, but I haven't checked that yet.

Kilty_2

Salesman told me that the economy of my brand new Picanto would improve over the first few thousand miles. So far (1600) it has went from 42MPG to 54MPG.

clever_username

It seems reasonable that it'll take the engine a while to reach its 'potential' when it comes to fuel economy. I remember hearing a story about the speed record set by a steam train: the man trying for the record deliberately picked a train that had been in service for a few months rather than a 'brand new' one that hadn't been 'run in'. Presumably performance and fuel economy in a car works along a similar principle.

That said, probably a few weeks getting used to how the car drives and you becoming accustomed to it will make a difference to how fuel-efficient the car is.

vikingaero

Most cars will be at their optimum MPG and power output after 10-12k of driving.

I wonder why you think you'll achieve the manufacturers extra urban figure? The manufacturers figure is obtained indoors on a rollling road with drag and friction allegedly factored in. There are so many factors at play for real world drivers - driving style, different tyres, different roads, gradients, weather, traffic, other road users etc etc.

As a rule of thumb I deduct 20-25% off the figures to get a realistic real world figure for driving in the congested South East.

WobblyDog

With my previous car, the average mpg I achieved was close to the official extra-urban mpg figure. I based my calculations on odometer and petrol-station pump readings over a decade.

I suspect this was because nearly all of my mileage is done on motorways, often at quiet times, and I'm sometimes seen trundling along at 60mph in lane 1 with the HGVs.

I was hoping that I would be able to average close to the extra-urban figure with the new car, but it's not happening yet.

LandyAndy

20 years ago I had a new car (Pug 205GTi) which showed a marked improvement in consumption after a few thousand miles. Recently I have had a number of new Mazdas (RX-8, 6, 2) and their consumption has not changed with use.

skiddlydiddly

There's more friction in a new engine, as the bits get worn a little(run in) then this decreases, power should increase and the result is(if you drive economicly) better mpg.

birkee

I'm not sure how anyone can help with fuel consumption figures here. I suspect they will improve over time, but....

I recall many years ago, the RAC(?) doing tests, and running a car for one mile from cold, and then stopping it and allowing it to go cold again. Then dong the same tests at something like 3 / 10 / 20 miles or something similar.
The figure for the 1 mile car was something ridiculous, like 4 miles to the gallon.

The point is, how do you judge MPG unless over a specific distance under specific conditions?
Worked with a chap who's Wife had a brand new Mini, and complained she was only just getting over the 40mpg. Had to point out to him, that as she worked about three quarters of a mile from home, she was doing very well at 40mpg.

skiddlydiddly

You just take an average, as it will be an average of what you do in the car then it will represent your own personal mpg.