Is it normal to get significantly less fuel economy in the winter? I'm in northern Michigan and it's been a very cold winter thus far. In fact right now is -35F. Does this have much bearing on fuel economy? I also use 87 octane.
Oh **** yes. Huge bearing on economy. It takes a lot longer for the car to warm up and get to operating temperatures. Assuming it can actually get to that in temperatures that cold. As well as all the time sitting there idling to warm up. You'll essentially be getting 0mpg.
Cold air = denser air, which requires more fuel to maintain the proper air-fuel ratio (this is why a cold air intake usually does not result in a fuel economy increase). Being -35F is an extreme form of that, so that is just going to be guzzling fuel to keep up with all the air coming in.
Also, cold temperatures increase rolling resistance between the tires and the road, further reducing fuel economy.
And as mentioned above, if you're remote-starting or idling the car to warm it up, prior to driving, then that's even more fuel - and it's fuel into a cold engine, which obviously requires even more fuel.