Get your car check for codes.

 

a common problem is a bad knock sensor, which doesn't trip the CEL so you'd never know unless you checked for codes.

 

I've been getting roughly 18-19 in the city lately, and I have nothing wrong with the car (and yes, I've checked for ghost codes.) The combination of almost straight city driving and it being winter (increased use of the heater) will reduce your gas mileage.

 

How does the heater affect mileage? B/C I know that AC does, but I don't know how or why about the heater?

 

The seat heaters, defroster (which uses the AC system to dry the air), and rear window defroster use energy that could bring down fuel economy.

The heater runs on hot engine coolant, which is there whether the heater core is flowing or not. Heat not pulled off by the heater would get removed in the radiator regardless. So the heater itself is essentially free.

Dave

 

I did not know the details behind it. However, I did notice the drop in mileage because I have to use the defroster quite a bit. I stand corrected on the explanation though.

 

Also, winter gas has a lot of addictives so your car would get less mileage.