Terrible MPG: What am I doing wrong?

What a silly statement. NO car is going to hit the EPA mileage in low temps and bad winter weather. It has nothing to do with car brand. And everything to do with physics. And personal driving style and driving conditions. If you drive all city, and are comparing to the combined EPA rating, you are comparing to the wrong benchmark. Not unlike saying "my bond fund didn't outperform the S&P 500!"

 

My outside temperature was flashing when I started the car today, and it's never done that. I thought that maybe there was an error.

The manual says, "The temperature display flashes for approximately 10 seconds when the outside temperature drops to approximately 3°C (37°F) or less, and then stops flashing."

 

I got a pleasant surprise yesterday on this journey. Set off in the afternoon, was fairly cold at 7C/44F, Eco mode, wore my wool overcoat, didn't use the heating/AC, and got higher MPG (77.8 UK MPG/64.8 US MPG) than normal (60 UK MPG/50 US MPG) in this current climate.

 

For more information & humo(u)r, check out this thread. 37 Degrees F | PriusChat

 

FWIW: On an RAF helicopter squadron, the crews were always concerned about the air temperature falling below +3Celcius because from that temperature down to freezing, water tends to become 'waxy' and will readily freeze onto rotor blades. This can include water vapour in the atmosphere condensing onto adjacent cool surfaces.

 

Your explanation sounds better than Tony's.

 

But perhaps, no more accurate.

 

Maybe freezes sooner due to wind chill and/or rapid evaporation too?

 

I'm next door in NH. My mileage for the past couple of weeks has fallen from about 55 to high 40s mostly attributable to winter formulation gasoline, heater use, and just this week mounting my snow tires. When there's actually snow on the roads, we can expect mileage to drop even more and when really cold weather hits it will cost us a couple of MPGs more. My worst ever mileage (in my 2010 before I traded) was in a blizzard with a couple of inches of snow on the roads and temps in the low teens. Traffic on I-89 was sparse but moving at 20 - 30 MPH; mileage dropped to about 38MPG.

Here's hoping for a mild winter!

 

I forgot about gas formulation.

My MPG dropped about the same percent the last two weeks -- no snow tires here, but two long trips on the Pike and NYS Thruway.

Anyway, the combo yielded my worst two tanks yet.

BTW, You can now sort 2016 Prius' by model on Fuelly. Not sure if that was always a feature, but I had never seen that before. Looked like they got good model info on nearly every 2016 participating.

 

I returned home from Virginia Beach on Saturday, got 53 MPG on the 600 mile trip. My last trip to VA was in August, I got 57 MPG.

 

I'm thinking it's not wind chill, but rather pressure drop. A wing (the rotor blades on a helicopter essentially being wings) has a low pressure region above the blade, and a reduction in pressure will cause a reduction in temperature.

 

... and condensation results. You've all seen the clouds forming over the wings of key aircraft pulling G. The dew point is linked to humidity, temperature and air pressure!

 

I suspect that is also why dad's pilot friend commented on carburetor icing being most severe at ambient temperatures significantly above freezing. Warm enough to carry plenty of moisture, which then freezes as it goes through the pressure drop at the throttle. In below-freezing ambient conditions, the air simply doesn't bring along much moisture, so the carburetor heat can more easily keep up.

Wind chill alone should not freeze liquid water except under extremely narrow conditions. The above-freezing wind brings alone a lot of heat to prevent freezing. The windchill charts are very specific to bare human skin, and do not apply to inanimate objects lacking continuous internal heat.

 

Assumption Time!
I'm going to assume the OP is doing nothing in majority "wrong".
I'm also going to assume there is nothing fundamentally wrong with the vehicle.

I would strongly urge the cessation of this behavior:

Cold Weather, Accessory Usage, and Short Drives all can add up to lower gas mileage numbers.
Two things I might do?
Check tire PSI...cough...cough...I inflate to the recommended PSI in the doorjam......

AND...

If you can....force a semi-long...highway road trip. See if a long drive somewhere doesn't result in your MPG going up. It should...even in the winter.

Otherwise, practice, time, and springtime should all result in increasingly better MPG.

 

Greetings to OP Censalata, from one Vermonter to another. I spent my early early years growing up on Lake Bomoseen. Wish I were there now!

Some memories of Vermont: snowing one August on the lake, foliage seemed to start turning on every labor day as it was a clear delineation between summer and fall and one Christmas with wind chills being 50 degrees below zero!

My current commute is 2.3 miles one way. With the heat set at 70 (battery not charged as I have a plug in and not always able to charge up) my mileage averages 36 mph in colder temps! Since owning this vehicle took a long trip and averaged 63 mpg in warmer weather.

Best of luck with your new Prius!

 

So, get a block heater, pump your tires to 40psi, and relax, enjoy the heated seats

 

I need to check mine again since we're in the 30's now (first snow this morning)... I had set them at 42/40 but that was in 50 degree weather, so I'm probably down a couple of pounds.

 

Good idea for everyone this time of year.