Hi all,

First post, apologise in advance. I've a 2012 Mk7 Fiesta, Zetec, and I noticed a few weeks ago that when I filled up the car (full tank), the estimated mileage on the car had changed.

It had gone from the usual 315+ miles (when I purchased back in July), which lasted for a few months, to around 275+ miles on the clock. Is there anything in particular, other than driving manner, that could cause this? As I've only had the car a few months and 40 mile drop is a bit weird.

Change in the weather affects all cars.

So you'd believe that 40+ miles would be due to weather changes?

So you'd believe that 40+ miles would be due to weather changes?

Seems an excessive drop in m.p.g. to me

What's the mileage on the car ?

When were the spark plugs & air filter last changed ?

When were the tyre pressures last checked ?

Seems an excessive drop in m.p.g. to me

What's the mileage on the car ?

When were the spark plugs & air filter last changed ?

When were the tyre pressures last checked ?

Mileage has just hit 50k. Spark Plugs/Air Filter last changed on purchase, July 2015. Tyre pressure checked last night, all in order on all four tyres! :)

How are you calculating the average m.p.g. ?

Tank mileage based on the computer in the car.

Tank mileage based on the computer in the car.

Noooooo . . . the only accurate way to measure m.p.g. is to brim the tank & note the mileage, then drive it until the fuel light comes on & brim it again & note the mileage & fuel needed to fill it up.

Then, calculate the mileage covered between fill ups & divide by fuel used - for example 300 miles driven, divided by 45 litres used, would equate to approx' 30.3 m.p.g :)

Tank mileage based on the computer in the car.

Your fuel computer is highly likely to be around 10% out . . . & possibly more if it hasn't been regulary reset

Your fuel computer is highly likely to be around 10% out . . . & possibly more if it hasn't been regulary reset

How could I go about resetting it if you don't mind me asking? :)

How could I go about resetting it if you don't mind me asking? :)

I'm not sure on your Fiesta t.b.h., but it's likely to be resettable by bringing up the trip mileage on the computer & then resetting by pushing the black reset '' button '' that i think is on the bottom left hand side of your instrument cluster ?

This info should be in the owners manual

Did you read my earlier post regarding properly calculating average m.p.g. ?

I'll have a little dig around. And I did yes, will have to work it out over the next week or so.

Bring up the trip on the left hand stalk and keep it pressed, it resets the trip.

my 63 plate fiesta is doing exactly the same. i know i've only travelled a mile driving economically and it says i've used 3 miles worth of petrol. then it sticks for around 5miles and starts again. i know i have no air leaks. cleaned the maf sensor and still the same. i'm thinking there's a problem with the computerised estimated mileage readout. i've put £10 of petrol in the tank (which is roughly two gallons) and have noted my mileometer reading and not the estimated mileage to see if there's a problem with it. will let you know what mileage i actually do when the red light kicks in.

So you'd believe that 40+ miles would be due to weather changes?

Car idling longer (if you let it warm up) cold mornings, using heating or air con, using front heated screen, it all adds up, oh and also the change in chemical make up to 'winter fuel' by the fuel companies.