My Prius 2008 #2 purchased in 10/07 has 3600 miles on it and the mpg is steadily decreasing on my screen. I mostly drive in town. I used to get 48 mpg and am down to 42.6 and falling! Why!? My driving is consistent.
The easy answer is "cold weather". Many factors contribute to the cold weather impact including ones you can do something about...checking your tire pressure and increasing to 42f/40r...remember that tire pressure drops when the air temp gets colder. You can do some grill blocking. You can install an engine block heater to pre-warm the engine in the morning before you start your day. You can reduce the temp your AC is set at. Other factors you can't do anything about. Be sure to read my article that discusses many of the factors that contribute to reduced FE.
Hi Carolyn, Welcome to Winter. This is normal. Its due to the cold. The bigger the difference in temperatures, the faster the heat flows from hot to cold. So, even with a closed engine thermostat, the engine and catylictic converter cool faster, and the computer runs the engine more to keep them up to temp. Also, the colder the engine is in the morning, the more its heated to get to operating temperature, which uses more energy, and that energy comes from the gas. Additionally, I am sure your probably using your defroster more often in the last few weeks. We have had allot of 25 to 35 humid weather, and one just cannot see out of the car without defogging the windows. That uses heat, and electric power for AC dehumidification. Besides these things, the tires are colder. If you have not brought them back to 42 front / 40 rear PSI, then the difference from 65 to 35 F will drop the tire pressures by 3 PSI. Additionally, colder rubber takes more force to flex. As it flexes, it warms up, but again, its warming up from as low as 10 F (in the last several weeks in the morning here in the west burbs) to a running temperature closer to 40 F. And at 10 F, you are most likely using the car's heater. That heat comes from the fuel burned in the engine. So the engine runs more to stay warm enough to give you heat in the cabin. Besides all this, there is the stage 3 to stage 4a transition. Stage 4 is full hybrid mode. Stage 3 is somewhat limited in hybrid actions the car will do. The thing that impacts the most, is that when gliding, the car will turn the engine on with any accellerator peddle depression. Rather than using electric drive, as when the car is warmer. And once the engine is on, it wants to stay on until you get to at least 35 mph. Then the car will jump into stage 4a, and you can glide again. Combine these things with shorter trips for gift buying, and more family activities this time of year conspire to reduce the mileage you will get. Allot of us use Grill Blocking to improve warmup time. Do a search on Prius Chat here for the topic. Also, search for "The 5 Stages" . Search on Engine Block Heater (EBH) if you have a garage for the car. All these things will help.
Please remember that all vehicles exhibit this kind of drop in MPG in cold weather. Some are affected more than others due to their already MPG (a % drop at 50mpg is more noticable than the same % at 15mpg). You also have better instrumentation that lets you know this is happening. So this is not really a hybrid issue so much as a general automobile issue.
Carolyn, I drive in Chicagoland, approximately in the same horizontal plane as Rockford. To see just how temperature directly affects the Prius' mileage, click the link in my signature for "Current Mileage".
Tony, Since Aug 06, your MPG improved consistently. Did you start blocking your grill? It doesn't explain why you got better MPG during the summer as well. I guess your car broke in? Or your hypermiling skill got better?
I'm guessing it's a combination of all and some other things. I did start blocking my grill as well as over-inflating my tires. And yes, my hypermiling skills have improved as has my route to and from work. There used to be a few lines under the chart explaining some key dates but somehow I lost that. I'll have to put it back in.
Mpg Even with this cold temps we are having in SE Pa., I still get between 45 to 48 mpg. Just be easy on the throttle (no jack rabbit starts and hard braking). I try to accelerate smoothly... 42.6 IMO is still not too bad.
