Fuel Economy on new car

FakeIrish

Morning everyone

We picked up a brand new Nissan X-Trail last week. We got the 2.2 diesel version with a reported 37 mpg. However, on my rough calculations we are only getting approx 28mpg and yet we are driving very sedately at the moment.

I'm aware that on new cars, they are not fully economical and takes time for the engine to bed down before becoming more economical. However, this does seems to be a remarkable low fuel economy rate.

How many miles does diesel engines needs to cover before they become more economical? And when this occurs, can I expect an improvement of approx 10mpg?

Thanks.

SVM

balsingh

The X-Trail is a big heavy car and 37mpg seems quite optimistic. I think around 30mpg is a good target to aim for.

J_P_S

manufacturers mpg figures are rarely achievable in my experience, they are usually optimistic at best.

Chris_VRS

As you have mentioned a new engine will need time to be run-in and with that the economy will increase although not by 10mpg!....all manufacturers fuel consumption figures are done in labratory conditions so are quite un-realistic!....the best way to calculate the economy is to look @ the figures quoted in the brochure - find the urban figure and the combined figure and find the half-way figure inbetween this is the most accurate way of finding what a car will be REALLY like!

for example - urban 20mpg, combined 30mpg = realworld mpg will be around 25mpg

BenL

Here is an extract from https://www.carkeys.co.uk advising how the official economy of a car is measured and why you will not get the figure out of your own car.

It's a bit like emissions testing. In fact, it is emissions testing. Very few people outside the motor industry have any idea how this works, so let's take a quick look.

Emissions tests are conducted in specially built labs inside car factories. The cars being tested (which make up about one percent of total production) sit on rolling roads - basically sets of rollers which are spun by the driven wheels. The test drivers then have to drive along a virtual "route" determined by European Union legislation. The route is about seven miles long, takes twenty minutes to complete, and is divided into two parts called Urban and Extra-Urban.

The test drivers follow a speed trace - accelerate from rest to 80km/h, then back off to 35km/h, and so on - and they have to be incredibly accurate. Errors of up to 2km/h are ignored, but the total permitted time for greater discrepancies is one second in the whole twenty minutes. Any more than that and the test has to be abandoned and restarted, to the great annoyance of everyone else in the lab. These testers are among the unsung heroes of the driving world.

Wait Till You Hear This . . .

In establishing the speed trace, the authorities had to allow for all the types of vehicle that would have to be put through it, including very slow ones. This leads to the amazing statistic that the time allowed for the 0-100km/h (0-62mph) part of the test is FIFTY SECONDS! Clearly, high-performance cars are not extended at all - the tricky bit is trying to make sure they don't accelerate more quickly - and it might seem that this immediately invalidates the test. On the other hand, there is a balance involved in the fact that the test doesn't include the equivalent of, for example, long periods of very light-throttle motorway cruising, when real-world fuel economy is much better than it tends to be in the lab.

At the end of the test, four bags of gas are taken for sample. Two are filled with the exhaust produced by the car during the Urban and Extra Urban periods of the test. The other two are filled with air taken from the lab (and therefore sucked in by the car's induction system) during each period; these may differ from each other by minute amounts, and they are required for comparison because there may be more of a certain gas floating around in the lab than the car itself produces. It's the difference between the ambient air and the exhaust emission that determines figures, not simply the emission itself.

The 3 part article is here

http://www.carkeys.co.uk/features/technical/575.asp

Ben