Why mileage gets worse in winter

I haven't fiddled with thermostats at all, so will defer to Mendel and others with more experience at them. I'll only speculate that there may be enough other cold air getting in, out of reach of any grill blocks, to keep keep things well cooled.

My '86 Accord's temperature needle moved around a lot in its old age, and having a shop replace the thermostat didn't change anything much. I didn't further troubleshoot, other than to sometimes turn on AC for the sole purpose of running both electric fans (engine normally used just one of them) for added cooling, quickly bringing down engine temperature.

Then my '97 Subaru had a rock solid temperature needle. I thought that was great, until getting a ScanGauge and discovering that the entire temperature range from 145F to 210F was condensed to a single point on that analog gauge. :-(

 

Have gotten the worst mileage of any tank...barely over 200 miles for me. Computer said I was getting 26 MPG. To be fair, its been -30 F out and my car rarely goes into EV mode.

 

Which grill blocking techniques have you implemented?

 

See you're in Fairbanks, Alaska (clicking on the zip code).

Do you have the block heater?

Short trips?

Garage parked or outside?

 

I've been driving a lot with the Hybrid Assistant app running. My outdoor temperatures lately have been in the 30-40°F range most of the time.... According to the Hybrid Assistant app I'm usually running engine temps under 60°C (it's displayed in C only) for the first 7 or so miles. During this time, the engine doesn't want to turn off much (in particular, engine temps under 45 C make it want to keep the engine on).

My driving, with average speeds around 20mph, gets me around 35-40mpg during the warmup period on such days; it's closer to 25mpg until I get the engine temp up to 25°C.

In the cold, the car can readily do 50mpg, but only after it gets up to about 70°C engine temp. All of the above numbers are based on dry roads; snow and ice worsen the numbers significantly.

 

One more reason L/100 km beats mpg.

50 mpg is 4.7 L/100 km
45 mpg is 5.2 L/100 km
20 mpg is 11.8 L/100 km
18 mpg is 13.1 L/100 km

The difference speaks by itself.

 

sylvaing you make a good point but I think you swapped numbers on the top 2 items;
"50mpg" shows burning MORE liters of fuel than "45mpg" in 100 km according to your post

 

Lol, it shows one more problem with mpg. I used Google to convert the two and didn't realise that the 50 mpg used imperial gallons instead of US gallons. It's 4.7 L/100km. I'll correct.

 

To convert I divide either system values into 235.2; works both ways.

 

2012 Toyota Prius (Gen 3) - January - February 2024: Total distance driven: 8,430 miles. Overall gas mileage: 73.6 mpg.