[Karsten (OP)]

Best gas mileage I get in the summer when it is hot. 40 mpg. In the winter when it drops below -10C it is quite bad. 27-30mpg. Why? Same route, same driving behavior. "Wicked cold" is today: -30C.

[Chemistry4me]

The petrol, or gas, needs more heat in the cold (I think!) making it less efficient.

[RD]

Air resistance (and consequently fuel consumption) is greater in the cold because cold air is denser: more aerodynamic drag.

[Chemistry4me]

Not to mention trying to drive through the snow! Even more resistance!

[lightarrow]

Furthermore, if you a have a recent kind of car, the catalytic exaust needs more fuel to work properly.

[chris]

Most of the increased fuel consumption is accounted for in the cold starting. Petrol engines especially need an enriched fuel mixture when cold because the fuel vapourises less well and so burns less well; the "choke" on the engine overcomes this by enriching the fuel/air mix many-fold (as opposed to manifold!), but consequently the fuel consumption rises accordingly.

The engine is also "stiffer" during a cold start because the oil is much thicker, applying more drag, and the resistance from other bearings around the car is higher when the vehicle is cold because the grease is more viscous and takes longer to warm up.

Chris

The fewer cold starts tjat