Someone mentioned to me today that their economy had dropped a little on their VW golf diesel. He remarked that this was probably down to winter diesel. I confess I was ignorant of the fact that refineries change their output as winter draws in to produce a diesel with a modified mix to reduce clogging caused by the waxy whotsits in the fuel (please excuse the technical terminology).

The upshot of all this is a reduction of around 5% in fuel economy due to the reduction in the fuels calorific value.

Being the sceptic I am I looked in to this and it all appears to be true near as I can tell. Mine has dropped its mpg a little recently. Not much but enough to notice. I had put it down to being more lead footed but it could be the fuel available at the pump. Combine this with rear heated windows, lights and an engine taking longer to warm and loosen and you have a recipe for less economy.

Anyone else noticed this effect ? I am new to diesels in that I have never driven one through the winter before.

Yes Mr Estate Man, I have indeed checked my tyre pressures ......Only joking, good post on tyre pressures btw.

I know in bygone days, lorries used to grind to a halt in severely cold weather, due to thier diesel turning to jelly! (Not the nice with ice cream type) You would see them on the news, stranded on the motorways!

Modern addetives help prevent this but I guess lower mileage and/or dearer fuel is the price you pay for getting all the way there without having a two week tea-break!

Anyone else noticed this effect ? I am new to diesels in that I have never driven one through the winter before.

Yes Mr Estate Man, I have indeed checked my tyre pressures ......Only joking, good post on tyre pressures btw.

Hi Raisbeck, yep...my garage has just taken delivery of it's winter diesel stock. You are of course quite right about the reduced miles per gallon. I have found I lose about 4-5mpg overall in winter for all the reasons you list. Petrol cars go through a similar thing too with winter petrol. The additive packs that are added to the petrol contain more 'sniffers', the additive that enables petrol engines to start and run more easily in very cold weather. However, those have a much lesser effect on the mpg figures as the calorific value is almost unchanged.

Oh, good input about not forgetting the spare wheel pressure on that thread...I should have mentioned it but forgot! I dunno...I'm getting old!!

Winter motoring will use more fuel. The electrical systems, including on some VAG vehicles have electric heating circuits for the coolant to aid warm up. Fans, heated windows, mirrors all add to it. Then there is a the weather, wet roads, wind all effect the rolling resistance. Winter diesel contains an additive to prevent waxing, spent a fuel cold mornings cleaning out tractor fuel filters..... I personally wouldn't put the winter diesel down to less mpg. The modern diesel engine doesn't sense for changes in fuel types like octane ratings on petrol engines which would adjust things in the engine management, so it would continue to use the same amounts of fuel winter or summer using the same engine load.