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Originally Posted by stefan4
One thing to bear in mind is that cold temperatures really effect diesel engines. Any thing below 5 degrees and its normal to see 10 - 15% reduction in economy. All of these are reasons why I have gone back to petrol in the shape of a 320i.
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Having driven diesel and petrol cars for many years, 10 - 15% reduction in mpg for diesels under 5-degrees, is something I support with data for my driving over the years.
The other factor I've observed, petrol typically has a much closer mpg to diesel than we may think, when we make short trips in winter time.
I posted these comments just this week on another forum.
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I've just crunched a few numbers for short trips, now that I have some data and can compare my F11 535i with the E91 330d, making the same trips, same sort of driving pace.
For my 5 mile mark, the mpg from cold is less than 10% more fuel for the petrol, even at 12 miles it only increases to about 13% more fuel. Takes around 30 miles before it is uses over 15% more fuel than the diesel. Add the price differential for fuel, that's 10 pence a litre in favour of the petrol at the moment (comparing premium fuels which I use). ....
It is when you start adding decent runs, the diesel engine will start returning the good mpg figures. That is where the petrol just can't gain the economy. My example, the diesel will around 20% less fuel. ....
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What that translates to, the diesel savings in winter could be less than 50% of what we may be expecting, (my example, the 20% difference on long runs, eroded to around 10% for short trips). And that is without the fuel cost differences, which currently reduce savings even more.
Most winters we get a cost premium up to 10 pence a litre on diesel fuel. This winter we peaked at 11 pence up here, still around 7 pence.
HighlandPete