The colder starts are bad for gas mileage, but overall it shouldn't affect mileage much. My climate control stays on 68F all year, and I tweak the "fresh air dial" to suit my needs.

All cars experience reduced mileage in cold weather, it has to do with the time it takes to heat up the engine to optimal temperature. During heatup, the engine does not fine tune the air/gas mixture, it does this only at normal operating temperature. You should expect a 5-10% decrease depending on the number of cold starts.

I know these are old threads regarding gas mileage. I've been searching these forums for a thread on whether gas mileage goes up or down with a seasonal change. I live in Maryland, a rather moderate climate, and have noticed that my mileage has dropped from around 19.6 in mixed use during winter to 17.0 mixed use in summer. I have a 3.0i. I suspect that the gasoline is highly oxygenated in winter as a smog reduction effort and not as highly ox'd in summer. It's a theory but may explain the seasonal decrease. Anybody have any thoughts?

Are you using your air conditioning now? Mine drops several MPGs if I turn on the a/c.

I just assumed it went down because, if like any other human on this rock we call earth, when cold, we leave the car run when we stop in someplace so its still warm when we get out.

I never let it idle in summer.... Just a theory....

Michelle, In Washington D.C. I don't know how I ever survived without a/c. The a/c in the car runs year round actually. I set a temp of 72-74 depending on the conditions. In the winter it doesn't cool but instead warms the cabin, but the a/c indicator itself is on year round. In winter I do adjust the three dots in the center of the console from 3 blues to 3 reds though (make a diff?). Maybe the compressor creates a greater drag for a/c in the summer. Just for chuckles (and because I like to solve a puzzle) I switched from Sunoco to Exxon gas. I have seen nominal improvement in this tank of gas - I'm over 18mpg but still short of where I usually track. I have recorded every gallon of gas I ever put in the car (no comments) so I will analyze the past 8 years and see if there's a trend there.

Don't use Exxon. It's not top tier. http://www.puff.com/forums/vb/images/smilies/nono.gif

Any name brand gas that has frequent usage (more fresh gas and decent tanks) is fine IMO.... I tend to add a lil additive now and then as gas quality seems reduced..

Between the Ethanol and Oxygenated Fuel....bottom line, less energy per gallon.

Don't get me started on those corn grower lobbyist. I still prefer MTBE gas

Not sure how to ID what a "top tier" gas is. I analyzed my gas since I bought the car 8.5 years ago. No real pattern emerged. I detect no seasonal variation by brand and time of year. The mileages above 19.x involved long trips. The red highlights I either did not record the brand or my daughter/wife didn't write down the proper information.

Here's a thought...I have 147,000 miles on the vehicle ('02 3.0i) and changed the spark plugs once at about 92K. Might that contribute to lower mileage?

No seasonal variation detected
Brand/MPG (average)
Love's*18.47Express*18.17Liberty*19.10Gulf*19.10Shell19.14Sheetz19.41Unknown19.50Wawa*19.60Exxon19.67Costco19.737-Eleven*19.90BP*19.94Citgo*19.94Circle-K*19.94Chevron*19.97Hess*19.97Sunoco20.01Rutters*21.09Getgo*20.71Royal Farms*22.78Mobil*22.78* Statistically insignificant (5 or fewer tanks)

www.topteargas.com


EDIT: Ohhh snap! When did Exxon appear on that list?!