G1 Prius MPG in the winter

The thread referenced pretty well covers the technical details. I would only add these minor comments:

• Mechanical frost and condensate removal - the engine takes about 5 minutes before it reaches 70C, hybrid mode. So scrape and wipe as much as you can before starting the engine to clear the glass and mirrors to drive safe.
• Windshield fluid - there may be fluids that have better deicing properties.
• Cabin heater is a manually controlled radiator - with the heater on and engine off, the cabin heater continues to cool the engine coolant. It normally doesn't matter for short traffic stops, less than a minute. BTW, it can be used on high temperature days to provide additional cooling if say the radiator fans come on.
• Defrost vs windshield directed - the two right-most settings include full defrost that actives the air conditioner to dry the air blown on the inside of the windshield. Sometimes it is needed but use should be only enough to clear the problem. Then switch to the next position so 'free' engine heat warms the glass to prevent fogging.
• cabin recirculate - reduces how much heat is needed from the engine BUT humans exhale water and this can fog up on the cold glass. Heating colder, outside air dries the cabin air, reducing window fogging. Sometimes on a constant speed, highway drive, it is possible to use cabin heat and crack a window to optimize the mix of outside and inside air to avoid fogging yet remain comfortable.

As the temperatures reach 40 F, I typically:

• use block heater 30-60 minutes - shortens engine warm-up to 70 C by about 1 minute.
• delay high-speeds - initially use 25 mph neighborhood route, ~1 mile, to reduce the cold, dense air effects on early engine operation and allow the engine to more quickly reach 70 C before the 50 mph blast on the cross town streets. It also clears the last of any fog or ice from windows.
• avoid higher speed, cross town streets - use the access road and lower speed, less frequently traveled streets. At higher speeds, the blast of cold air (aka., wind-chill) can rob a lot of heat from the car even with a radiator inlet block. Also, often winter weather with precipitation, leads to more accidents on the higher speed streets.

Bob Wilson