[id5]

Originally Posted by RoyMacDonald

Mpg is higher in the summer than the winter with diesels by a significant amount. Can be up to 28% worse from my experience. A number of factor contribute including Cold air which is denser than warm air. http://www.scientificamerican.com/ar...uel-economy-o/

The fuel is denser when it is cold, there are more hydrocarbons per litre, subsequently there is more energy in each litre.

As the article suggests, the reasons that they are finding a lower MPG in winter are other factors such as heating the car up before use, windshield wipers and defrosting devices, tyre slippage, etc