Fuel Efficiency Drop
 

I have notice my efficiency drop from about 7.3 L/100km to 8.5 L/100km with the colder weather on the exact same daily commute. Has anyone else had their cars drop this bad? The only other change was i put winter tires on, but the first week they were on i still got 7.5 L/100km.

Well colder weather will have an impact. And it can be significant if the trip is not long enough to achieve full enough warmup to balance off the richer running when cold. Are your winter tires the same diameter? Some folks think the car can compensate for this somehow, but I have never seen an explanation of how it would do this?

That's about what I saw over the last year, summer average was ~ 8L/100km in the city, winter went to ~10-10.5L/100km once it got cold. I track every tank and I also noted that the dash fuel consumption reports roughly 0.4 to 0.5L/100km lower than the actual. And this has been consistent for every single tank I have put in it. So, you're likely doing even worse than you think unless you calculate the numbers yourself.

Winter blend gas is here bud. The specific blend of fuel at the same octane rating will have less energy per litre of fuel.

http://jalopnik.com/what-you-should-...g-i-1450089585

Yeah I started noticing that too on the BRZ. Same thing when I had my Civic, I tracked every tank for 4 years with the exact same trend.

Yep.

I figured all that. My tires are the same and I track every tank with an app on my phone. my Cobalt wasn't affected as bad, just wanted to make sure this was more or less normal. Thanks for the replies guys.

It's a combination of longer warm up times (less efficient while warming up), the different blend of gas, and typically slower commute time when roads are bad

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The stock tires too are made for better fuel economy and putting on winters (in particular, but really any tire) will lower the fuel economy slightly (if you were running the stock summers).

That sucks. I hate being at the mercy of big corporations.

Higher density air due to it being colder means the matching and appropriate air/fuel ratio mixture must be compensated for accordingly.

More air, more fuel. Simple stoichiometric balance being maintained.

Yes, that is true. But due to the air being more dense you would actually require less throttle to accelerate the same. "The air being more dense" isn't the reason you burn more fuel. Longer warmup times + thicker oil on startup + winter gas + less efficient tires is your reason.

Air density is one of many reasons.

http://www.metrompg.com/posts/winter-mpg.htm

The only part related to air density in that link was aerodynamic drag. They generalized that aerodynamic drag increased 2% per 10 degrees f. It isn't anywhere near that simple, and can't be generalized that way. Speed would be a variable which throws that number out the window. Also the Source for that info was a Cummins engine website, likely referring to large transport vehicles.