Anybody have any plausible reasons why my MPG dropped like 5-7 mpg.....I know im coming up to another oil change and ny uses the winter mix fuel...but im avging 19.9 mpg on every fill for the last 2 fills. I'm not even driving spirited and trying my best to maintain a 55 highway speed with gentle acceleration. Could it be alignment?

 

Could be.....also check your tire pressure. I reach the optimal mpg around 65 and 70 mph range.

 

There may be a number of reasons. The two I have the most experience with are:

a) Cold - Temps in the 30's or below hit your mileage by 2-3 MPG
b) I'm not 100% sure what winter gas is, but I do know that 10% Ethanol blends will also lower your mileage by 2-3.

I'd be willing to bet it's a combo of those two (or maybe just the fuel) if it's that sudden. Other things like alignment, tuning, air pressure in tires, etc. would not make that big a dent in your mileage all by themselves. Road conditions / traffic also can have a big impact - if you're doing stop-and-go because of the weather or having to deal with bad roads.

 

Definitely, cold temps will hurt MPG because engine needs to be hot to work at optimal performance. It takes longer for the engine to warm up and so by the time you get to where you are going, it just barely "warmed up" and you turn off the engine, assuming that you drive for less than 10 miles (I have heard). This is normal for winter.

 

maybe we should lower the idle speed =]

 

Winter gasoline has more oxygen added to promote easier cold startup and lower emissions. I am convinced that winter gas has a *lot* to do with mpg dropping this time of year (a bit more than air temperatue alone). However, 5-7 mpg is significant. You shouldn't notice more than a 2-5 mpg drop. If more than 5, then there are other factors at play.