Fuel Consumption

repeatoffender

Hello I am driving a new 1.3 petrol 5 door hatchback. The fuel consumption is showing average 34 mpg and the manufacturers state 42 mpg urban driving. This car rarely does more than 6 mile journeys at a time and the aircon has been used permanently over the last few weeks.

For those in the know - will continuous short journeys and aircon actually make this difference or is some of it because of the way the manufacturers test their fuel consumption estimates?

Thanks

facade

Both questions have the same answer - yes

The car uses more fuel warming up, which will likely take 1/3 of the journey, aircon uses a little more fuel, and the "tests" are done on a rolling road to simulate urban driving, then the best possible figures are quoted.

Also your brand new engine takes a few thousand miles to free up and become more economical.

whatmichaelsays

repeatoffender wrote: »

Hello I am driving a new 1.3 petrol 5 door hatchback. The fuel consumption is showing average 34 mpg and the manufacturers state 42 mpg urban driving. This car rarely does more than 6 mile journeys at a time and the aircon has been used permanently over the last few weeks.

For those in the know - will continuous short journeys and aircon actually make this difference or is some of it because of the way the manufacturers test their fuel consumption estimates?

Thanks

The official figures are done under lab conditions, with the car effectively on a treadmill. They reflect 'best case scenario' and don't take into account:
- Extra weight (luggage and passengers)
- Low tyre pressure
- Headwinds
- Engine temp
- Your driving style
- Traffic
- Air conditioning
- Frequency and force of braking
- Any other variable you can think of.

They're useful as a point of comparison but rarely reflect real-world driving.

If you're regularly driving the vehicle cold, with the air con on and on short journeys (I assume in rush hour city traffic), then your MPG will fall.

repeatoffender

Thank you very much - it always looks great on paper - and a friend said just turn the aircon off - but clearly it is so much more than that

LandyAndy

I drive a 1.3 5dr hatchback. My usual journey is 5 miles. I always have the Aircon on. I get a steady 45 mpg and have done for the 55000 miles I have done from new nearly five years ago. The manufacturers figures are 41 urban, 67 extra urban, 54 average.

RichardD1970

Have a look on here, http://www.honestjohn.co.uk/realmpg/ to see how you compare.

keith1950

The fuel consumption is showing average 34 mpg and the manufacturers state 42 mpg urban driving

The official figures are done under lab conditions, with the car effectively on a treadmill

From practical experience over the last 45 years I have found that actual figures are usually around 6-7 mpg. lower than the manufacturers idealistic test figures.

kaya

I seem to recall that when they changed the criteria for the test and re-tested the Prius is was rubbish so far as MPG went

Buellguy

kaya wrote: »

I seem to recall that when they changed the criteria for the test and re-tested the Prius is was rubbish so far as MPG went

Suppose it depends what you use it for. Round town probably superb, long motorway journeys, probably rubbish (hence whyI don't have one)

MEM62

You will NEVER reach the MPG figure quoted by the manufacturer. They are obtained under optimum conditions and are allow to 'prepare' the cars for these tests. (They even tape up vents & door seams and remove windscreen wipers to reduce drag, over inflate tyres for less rolling resistance and even remove things like the battery to make the car a light as possible)

Short journeys of the type you describe are no good for decent MPG. They are probably not good for the car in general either. Once every couple of weeks or so try to give the car a decent run out.

droopsnoot

Also don't assume that the figures showing on your dashboard for average MPG are necessarily accurate.

The only way to get a proper average MPG figure is to brim the tank, drive for a week or two (until you've used maybe 75% of the fuel), then brim the tank again. Compare how much fuel you put against the mileage since you last filled up, then you can calculate the "proper" average MPG figure and compare it to what the computer tells you. Yours might be spot on, of course.