What is exactly the best temperature to drive in in summer: 30 degree C or 20 degree? High or low ( or is it 15 or 10 degree C). And in winter, should I drive when its colder, like -15 degree C or less, or warmer (like -5 degree C) would give me a better FE. And I know that during winter, the FE is way worst then in summer, but why. Would like some precise explanations plz (because I know there are some great mechanicals in here).