San Francisco is not that cold but getting chilly. Last month my MPG drops from 45 to 41,42. Past several fillups I used auto-AC, it works! back to 45!
That is not going to have an effect on the increased rolling resistance with wet weather, cold weather, winter blend fuel and increased air drag. BUT, anything that you can do to reduce the negative hit is a good thing. Can you provide us with more details on how you tested this?
