Cold weather mileage hit

I bought my 2016 Prius Two Eco in September, new with about 269 miles. The gauge was showing 69.0 mpg lifetime miles. By the time I got it home (roughly 100 additional miles), it was up to 72.0. The dealer had filled the tank for me, and I'm not sure what kind of fuel was used there. Since then, I've been using ethanol (mostly 10%, one tank at 15%) and it has gotten colder since Sept. I think the coldest when driving was somewhere around -10F to -20F. I've had a lot of days that were warmer, but I still had to run the defrost at higher fan speeds (i.e. gas hog) because the temp. I set to when using auto HVAC wasn't good enough to keep condensation off the windshield. Additionally, there have been some days with snow and rain, which I think cut mileage. Finally, wind seems (subjectively) to have been against me on a lot of longer trips.

I'm now at almost 6K miles and down to about 52 mpg lifetime. Needless to say, I've not been happy with mpg lately. I'm not sure if the ethanol is lower mpg than if I were to use normal or premium. What I am sure of: Using the defrost as much as I have had to at the high fan speed is affecting mpg.

 

Have you checked your tire pressures? My non-Eco was set at 32 by the dealer. Tire pressure can affect mpg. So can winter blend fuel. My son had noticed the fuel hit for years with his Prius.

 

No, but I'll make a note to do that sometime soon. The tires came filled with nitrogen, and I have not had any alerts for low tires. But I also realize that the low tire sensors won't pick up slight under-inflation.

Should I switch away from ethanol? It is cheaper in my home state (subsidized with lower tax) where most of my gas is purchased. If there is a nominal difference, I would stay with the cheaper gas and be better off anyway.

 

Good question. Here non-ethanol fuel is about $.50 per gallon more expensive. People generally use it for garden equipment, especially 2-stroke cycle engines. In fact, some manufacturers recommend against ethanol fuel in their 2-stroke engines.

 

My gen 4 during spring, summer and fall has been averaging 62mpg in new Jersey. Cold temps in winter below freezing mpg dropped like a rock. Last tank was down to 50 mpg. Wondering if there is something wrong?

 

50 mpg in the dead of winter is still very good.

 

Nothing went wrong, there is more rolling resistance for the car, the air is denser, you have to have the heater running - all of that drains MPGs

It will rebound back to the 60s once spring rolls around

 

Besides all the physics pulling mpg down (in winter), I think the car's programming shifts, purposely delays engine shut off, etcetera.

 

How and where you are driving makes a big difference to mileage. Low speed city type driving gets higher mpg. At higher speeds, such as open highway, it takes longer distances for the mpg to increase to 'good' but not as good as city! YMMV.

 

Stop-and-go city driving can lower your mpg, though. People here are in too much of a hurry. They accelerate fast so they can brake fast.