I live in the North-West of
I live in the North-West of England and this is my first winter with our Prius. The temperatures here are presently ranging between -5 to +5 degrees Celcius, and I have to say that fuel efficiency has dropped around 20 mpg according to the computer. If I use my 'pump to pump' measure, the difference is around 15 mpg, but this is still significant.
It is true that our old car's efficiency used to drop in winter as well, but to a lesser extent. I have to say here that the Prius is still far more economical at 45mpg than our old Golf (which used to get around 25mpg in winter, despite the claims of 38mpg).
Having monitored the situation for a few months, I have reached the conclusion that there are a number of factors:
1. The general increase in consumption caused by heaters, engine components and other cold-weather-specific engineering being pushed far harder. The engine is required far more to run these appliances.
2. The drop in the cold-weather benefit in conventional motors whereby the efficiency of the car is increased by 3-5% due to cold fuel insertion (in cold weather, you can get a substantial amount more fuel in the tank. This would be negated slightly by the Hybrid's lesser reliance on simple fuel).
3. I've noticed that the battery fills up quicker and indeed has actually charged completely on a few occasions (something that never happened in summer). At first I attributed this to a better battery performance in cold weather, but have since learned that it is more likely that the battery capacity is reduced in cold temperatures and the computer is merely showing the present limits of the battery rather than the general capacity.
I'll see how it goes. We are due a check-up as part of our sales service, so I'll ask the experts then.
I have a 2002 Prius. I've
I have a 2002 Prius. I've been taking relatively accurate measurements of all my fillups. Recently I added to the spreadhseet the average temperature in Central Park (I live on Long Island) and mapped it to the average temperature for the month. There are some variations but the angle to the trendline is significant. (The trendline is around 40 MPG at 30 degrees and 45 MPG at 65 degrees.) The ironic thing is that it is so linear. Hot weather doesn't impact MPG. (In fact it might even be more severe but I have a high data point of 40.51 MPG at 24.7 degrees that might be throwing off the tendline a degree or two.)