"Winter Diesel"? - anyone else noticed a drop in MPG?

[dannyDC2]

This is not the thread I though I'd ever make on Pistonheads, but here we are so let's just go with it.

Has anyone else noticed a drop in MPG over the past week or two? I'm down 5-8mpg on average, doing the same trips in the same conditions.

Granted the car does take a little while longer to get up to operating temps, but when discussing this with a mate he suggested that fuel companies change diesel slightly during winter, and that could be the cause of the decreased fuel economy.

I noticed this most last night coming home from Hull, cruise set at 80 leptons would normally net me a 48-50mpg average. Last night it was 42!! Yikes.

So this winter diesel thing - myth or not?

[dannyDC2]

Thanks for the replies - pretty interesting stuff!

[dannyDC2]

Loyly said:

I've always wondered, how much does using the heater effect the engine warmup time? Naturally, the first thing you reach for when you get into a cold car is the heating control. You feel that air flow gradually warming up as the coolant heats up, and of course, the oil temperature lags some way behind. How much cooling effect does using the heater have? It's drawing heat from the cooling circuit, but does this cause any net loss to the overall coolant temperature, and does that slow the overall engine warmup down?

On my A4 it makes a massive difference. So much so that I switch the climate control off until it's at least above 50c on the temperature gauge!