More on fuel economy

The first few weeks I had the car, the temperatures outdoors rarely went above 20º—during the day. Nighttime temperatures were well below zero. One of the secrets behind the car’s “super ultra low” emissions is a 3-liter vacuum bottle for storing coolant at high temperature. (An engine is more efficient when warm; more efficient engine results in lower emissions.) It takes about three days for the heat in that bottle to dissipate. By my not driving the car much, heat had to be regenerated for that system to work efficiently.

I figure the car’s automatic climate control system was also eating up gas mileage. Climate control—heating and air conditioning (A/C)—in the car is totally electric. Air conditioners everywhere consume massive amounts of energy. Not surprisingly, the Prius must kick on its (conventional) gas engine to generate electricity to run A/C. You may wonder why I’m mentioning A/C for a car bought in January... in New Hampshire. This is where I part company with automakers. I don’t agree with the default that A/C comes on automatically when defrosting the front windshield. Sure, dehumidified air helps defrost the windshield faster; however, at some point, one can continue defrosting the windshield without A/C. Sure ’nuff, in the Prius, the climate control in automatic mode defaults to having A/C on for defrosting the front windshield. You can even hear the gas engine cycling on and off. No wonder mileage plummets in cold weather, which the car salesman had warned me about. (Except he didn’t use the word “plummet.”)

It took me about 10 miles down the road from picking up the car before I realized the ramifications of the “auto” setting in climate control. I know, mea culpa, I’m strange: I like cold. (I’ve worn shorts for two years straight now—right through the winters.) However, leaving the Prius climate control on “auto” is guaranteed to offset some of the energy savings from the hybrid technology, no matter how low you set the temperature. Why? A/C will always be one of the automatic components in the (fuzzy) logic used to defrost the front windshield. (“Fuzzy logic” is a category of software programming, sometimes mislabeled as “artificial intelligence.” There’s no reference to fuzzy logic in the owner’s manual, but let me assure you that it exists in the Prius “climate control.” Japanese industries have been quite advanced in the use of fuzzy logic. By the way, fuzzy logic is the technology behind making elevators slow to a smooth stop.)

I suspected that the Prius gas mileage is somewhat dependent on outside temperature. Keep in mind that conventional cars (gas-powered) are not as efficient in cold weather as in warm weather. The Prius has an internal combustion engine; natch, it’ll be affected by cold weather. Now add this: Batteries are also not as efficient in cold weather as in warm weather. (Ask anyone who uses a handheld GPS unit during the winter!) The Prius’ hybrid engine is powered by electricity from a bbiigg battery; again, natch, it’ll be affected by cold weather. That’s two strikes against high gas mileage during cold weather months. A couple of other Prius owners, having read my explanation here, have confirmed that.

(Gas mileage should also improve after the car’s break-in period. Toyota claims the Prius break-in period is 600 miles. Oh? Seems mighty short to me for the mechanical beast called a “car.” Anyway, maybe other Prius owners who got their cars during warm-weather months can confirm whether the car’s gas mileage is affected by a break-in period.)

Also not helping my fuel economy is that I live between two major hills. No matter which way I go from the house, I have substantial hills coming and going. The Prius “real time” gas mileage meter shows a significant drop in fuel “economy” when crossing these hills. Like in the low teens mpg.