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usually my polo gets at least 60mpg just going to work and back, even dottering around town and likes, hell it even goes into the 70's on the motorways but the last few weeks it's dropped drastically, i can barely hit 55mpg on the motorway and town driving results in 35mpg.
I have always used super diesel when filling up aside a month or so back, apart from that the only other thing i have done is disconnect my battery and turn my ignition on/off to reset some VAG codes.

Anybody have any ideas if i have caused this or a certain part has failed? my knowledge of diesels in comparison to petrol engines is shameful.

I have a 2011 1.2 bluemotion diesel.


Cheers,
Kyle

cold weather will mean you get a drop in fuel economy.

but on the plus side you also get more power

Winter weather means denser air, which means a far more efficient burn and actually gives better fuel economy as less fuel is required to make the standard burn/combustion

it also takes more energy to heat up the air in the compression cycle to the auto ignition point

OP; the chances are, the diesel you’ll be buying now is winter diesel, which gives fewer miles per gallon than diesel sold at other times of the year.

Indeed. A lot more additives this time of year to prevent waxing

As already posted - cold weather has a fairly large impact on mpg.
On a cold morning our Fabia 1.9 tdi takes much much longer to warm up ( at a guess approx 4 times the distance) for the mpg figure to rise to (say) 50mpg,whereas on a warm summer morning the mpg readout will be up at about 50 mpg by the time we have gone a couple of miles down the road.This is caused by thicker oil due to low temps - everything on the car will be stiffer/more draggy and also the car may have been left to warm up/defrost before departure.Add in more use of lights/heater fans/heated windows and mirrors - all of these cause drag on the engine which soaks up power and we do not get anything for nothing in life.
Like you - in the warmer months our mpg on a cross country single carriageway journey can be up in the high 60's by the time we have travelled 30 miles ish but I would only expect 50-55 mpg as an overall average during the winter.
As also already posted - winter diesel does not help either - better to lose a few mpg's than have your fuel 'wax up' though.

kyle92 wrote: Thu Nov 23, 2017 7:33 pm Winter weather means denser air, which means a far more efficient burn and actually gives better fuel economy as less fuel is required to make the standard burn/combustion

denser air means more oxygen per unit volume of air

so more fuel will be needed to keep the afr right and it not run lean

Dink wrote: Fri Nov 24, 2017 8:49 pm

kyle92 wrote: Thu Nov 23, 2017 7:33 pm Winter weather means denser air, which means a far more efficient burn and actually gives better fuel economy as less fuel is required to make the standard burn/combustion

denser air means more oxygen per unit volume of air

so more fuel will be needed to keep the afr right and it not run lean

Diesels are perfectly happy to run 'lean'.

Air/fuel ratio is adjusted according to mass of air, not volume.

You also forgot that the ECU needed to monitor and control fueling is the same ECU which controls power output.

I concede that the current weather and the winter fuel will have an impact on my mpg however i an dubious of it dropping from over 65+ to less than 50 now, it just seems to sudden and too big but unless anyone has any other ideas of what it could be then i guess i will have to settle for that.
The help is appreciated, apologies for the belated reply also.