MPG issue

[Bandit127]

If you went to work at 70 mph with a tail wind of 30 mph, drag is equivalent to 40 mph. If the wind was the same going home your drag equivalent is 100 mph.

I can get up to 10 mpg difference on a windy day going 50 miles up and down the M3 (which is pretty much in line with the prevailing wind). On a still day it is about 2 mpg.

Dry roads vs rain + headlights is worth an easy 5-8 mpg.

Aircon. Not so much. I haven't been able to see aircon off/on in a diesel ever. In a petrol, not since the first generation of aircon equipped cars in the UK (and back then it could rob 10 mpg).

[bgbazz]

Interesting you should bring up the aircon stuff. I've checked on my 1.9 a couple of times...motorway speed, flat road  on a fairly warm day (around 40 degrees) and she's drinking 4.1 l/100...turn off the a/c and reading drops back to 4.0, so it makes very little difference. Headlights  must be lit at all times, so they are no factor for me.