Just want to be clear to everyone: there are 3 or 4 reasons our cars achieve higher MPG In warmer weather. By far the BIGGEST reason is.....your engine WILL run at operating temperature whether you like it or not. In COLD weather, your engine must run more and longer in order to stay at operating temps. That hurts your mpg. In higher weather, the engine will stay warm much longer so you can coast or do your favorite techniques longer!! By operating temperature I mean water temp aprox 195F and oil temp aprox 205F......
right! and colder air is denser as well, and there's more tyre friction, as well as mechanical friction. and batteries are less efficient. and using the heat will cause the engine to run more