Cold Weather Fuel Economy

[benjdm]

Originally Posted by ZooPrius

I had the same kind of jump in my milage when I inflated the tires to 42. Unfortunately when the temperatures are in the zero range I can't find an air pump that works that low which is when I really need it.

I always just use my bicycle pump. It gives me a lower back workout, too.

[nhguy78]

My fuel economy tanked in November when it started to get regularly cold in New Hampshire. This was only due to me warming up the car so I don't have to shiver trying to back the car out of the driveway into a dark street around a blind curve.

When I picked up my darling I was regularly getting about 49-50mpg. At it's worst I was getting about 40mpg. Right now thanks to moderated temps, I'm getting 43-44.

[donee]

Hi Zoo... and ben...,

Most of these carryable battery packs have a built in pump. And its a good thing to have around if you do not close the hatch all the way and run down the battery.

Hi All,

For a data point, started the week with a 7 F startup, had a 50 degree day , and now back in the mid 20's F. Finished the week at 58.9 mpg, but then had some errands around town today and ended up at 57.2 mpg. The warm day was one of the worse mileage days. The Prius tends to want to keep the engine running when the weather is warm, and engine temp is above 76 C. With the stops in my route, the car can be in and out of Stage 4 a few times. And each time there are lost gliding oportunities. One of the best drives home was when it was 25 F, on Friday, and got 64.9 mpg for that trip alone. Every gliding oportunity was had and even glided through a few green lights timed very nicely, thank you. On the warm day (50 F) drive home the mileage was only 52.x. Since Tuesday I have been running 80 % lower grill block.

One of my errands this morning was to go to the Sec. of States office for a new plate sticker. For some reason the re-up never appeared in my mailbox. To avoid the rush, I was there at 7:30 am and 20 F. Its about 5 miles from here, so the quick shutdown impacted my mileage. Then I went over to a grocery store about 2 miles from the SofS office. This is on the other end of town. The Grocery store did not open till 9 am. So I left the car in the lot, and got my walk in early. 2 hours later I am out of the store and drove home about 4 miles. Its those short trips that effect cold weather mileage really. For the 23 mile drives back and forth to work, 25 F weather is actually very good.

The reason the Prius wants to idle the engine during what would be glides, when the weather is above about 37 F and the engine is in the 76 to 82 C range during the warmup period is a mystery to me. I am trying to figure out how to stop that from happening. As you can see it s good for another 10 mpg on the 23 mile trip, if it can be avoided. Part of this is the thermostat opening up. The car gets to about 82, then all of a sudden, its back down to 76 C. And that reinitiates a Stage 3b to 4 transistion. If your in a driving enviorement with lots of lights, you can go through that twice. In the colder weather maybe the thermostat is just opening gradually, rather than going full open all at once.

[PriusSport]

You should be able to get in the low 40s mpg in Minnesota. I'm getting about 45 mpg this winter in PA--lots of short trips.

[bwilson4web]

I've been tracking my MPG for over three years along with the temperature. Recently I took the records and performed a weighted average of MPG and temperature to make these charts:

For our metric friends:


Now we don't get much sub-freezing weather in North Alabama but I recorded this set of data in January 2008 cruising at 65 mph (0.8% error on those tires: )

TempF TempC density_kg/m3 %_density MPG
15 -9.4 1.34 111.7% 47.5
32 0 1.29 107.5% 49.3
68 20 1.20 100.0% 53.0
85 29 1.17 97.5% 54.4

(Thanks to Ken@Japan who provided the air density data.)

Vehicle aerodynamic drag is proportional to the air density, which is a strong function of temperature. Humidity also has an effect but minor compared to temperature.

Bob Wilson