I live in Toronto and it's been cold lately. I notice my last tank did not get me my usual mileage. The only thing I can think of is; I've been using my heat alot. It is true your car uses up more gas when the heats on?

 

Just running the heat does not do anything to gas mielage. When you turn the **** from blue to red, coolant flows through the heater core from the head, and a door opens in the heater, letting air pass through the core (looks like a tiny radiator) where it is heated and blows onto you.

What's probably causing your gas mielage is either the gas station switched to gas with MBTE in it as many do in the winter for moeemissions, at the expense of mielage, or because it is cold, it takes longer for your car to heat up, so it is running on it's warm up fuel maps more, and the warm up maps use more gas.

 

Yeah. I have been getting less and less mileage on a full tank than I usually do. I live in kansas and the weather has been in the high 30's-low 40's and my gas mileage is not as good.