Don't know if this should go in the economy section or not. Just wondering because I've googled and it appears that cold fuel burns less efficiently? I know colder air has more oxygen in it. I haven't been on in awhile, but I didn't see any winter mpg gripes on the first page, so I thought it might be safe to post this. My AFR's are suprisingly close to where they need to be with the POS black box in open loop SD, so I don't attribute the loss to that. MPG is the same as last year when I was bone stock with a stock tune and O2's, so I rule out that as well. I'm entertaining the thought of fitting a thermostatically controlled fuel heater if I can find a cheap enough liquid to liquid heat exchanger to use coolant to heat the fuel up a bit more than ambient if cold fuel is the cause. I found a good bit on diesels and fuel temps, but not too much on gasoline.