I'm glad you posted up. I'm running around thinking I need plugs or O2 sensors.

I'm down to about 13mpg. Hopefully it'll get better once the warmer weather and better gas come around.

 

Well i'm down 1-2mpg after my header install and I thought it was because i'm running rich and need a tune...car also drops to 400rpm after a shift into either D or R and the lights dim and it gets super weak but hasn't died yet.

So maybe it is winter gas? This is the first time in my life i've heard of that though.

 

Do any of you guys take into consideration that you may have your vehicle sitting idle for longer periods waiting for it to warm up? This is usually the reason for worse fuel economy in the winter.
The fuel composition in the winter does have to use a fuel that has a higher reid vapor pressure to make sure the fuel lights off quicker. The additives that in the fuel do not have as much power per gallon, btu's, and therefore you get less fuel economy.

But still, the biggest thing is driving style. Also, it does take more power to push through snow and, probably not to serious, colder denser air will be harder to push through than lighter warm air.
Again, I don't think that has to much to do with it, but it would be cool to figure out if it did or not.

 

I don't let my car warm up any more or less thgan I usually do. I wait for the oil pressure to top out, then I drive away. Also, snow here in Chicago hasn't been a problem; we've only had two or three significant snow storms with accumulation. Having said that, my fuel mileage has dropped 60 miles from a tank since the time that winter fuel came around here, in late October I think. I get around 260 miles out of a tank in the sumemr time, and now I get consistently around 200. It's been pretty cold though, so the last couple tanks I've only gotten around 180. When the warm weather comes back around, I will report my mileage back here.

 

My beater is a 1999 Grand Am and I usually get 19mpg city driving. I checked it recently and was only getting 17. I thought my O2's were screwing up as well. I guess it is just the winter gas. I even switched brands with the same results. I went from Sunoco to Shell. Maybe I will try Sheetz gas next time and see.