Okay, if a couple of other guys on the board hadn't mentioned it first, I'd think the idea was crazy, but the winter killed my Subaru's gas mileage. I started driving my 95 Legacy wagon last fall and it averaged 24 mpg for the most part. When winter hit it dropped to 22 first and then to 20. I was disappointed with 24, but 22 and 20 was obscene. I read a couple people say that their Subaru cars went down in gas mileage during the winter. Sure enough, it's been warm (even hot) and sunny out and now I'm hitting 24mpg again. Weird...

I wonder if this would have anything to do with cold air being more dense in the winter time...? Any physics majors on here? :cool:

Three factors (that I know of) worsen your gas mileage during the winter:

1. In some areas, a different blend of gas is sold. It may not get as good of mileage.

2. When it's cold, your engine spends longer warming up. During warm-up, it runs very rich. This is a much bigger factor for people whose driving is mostly short trips.

3. Cold air is slightly denser than warm air, so more power is available to you. The same throttle position will draw in more air and gas and produce more power with a colder air charge.

Depending on where you live, the local laws require the gas companies to sell oxygenated fuel in the winter months to reduce certain pollutants during that time...then switch to different mix in the summer. Depending on the "designer" fuel specified by your locality, you may experience a 15% drop in fuel mileage with oxygenated fuel during the colder months. Typically the fuel is oxygenated with MTBE...the stuff that leaches into the ground water and hurts fish.

This is the first car I've ever seen drop in mileage during the winter, so I wonder if that's a quirk of Subaru's? (Or maybe just 4 cylinder Japenese cars...) I can live with 24, so I'm not gonna worry again until January rolls around again...

All of the vehicles I have ever owned dropped ave mpg in the winter when I was using it to drive to work. Its the warm up phase. I only have to go 4 miles to work so the car barely gets warm when the temp drops below freezing. My Fraud Ranger goes down to 14 sometimes. I havn't noticed any difference on the highway.

d.

and San Mateo CA is a mild climate. It used to be much worse when I lived in Maine because at 20 below zero we would warm the cars up for quite a while to clear the windows, and then you had to get that cold oil and grease moving in all the bearings in the drivetrain.