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Car Forum / Toyota / Prius / March 2006Winter Gas Mileage
I had the same problem you are noting. I changed the air cleaner filter and the mileage went back up to 50+. Also, make sure your tires, whether they be snows or not, have the correct air pressure in them. Recently, we've had some real temperature swings in our area, with several days in the 30's followed by several days in the 50's, and so forth. I've noticed the gas mileage always goes down significantly in the colder weather. I used to think it was the winter gas mixture, but now I'm thinking it might be due solely to the termperature. I know colder air is denser and thus wind resistance is greater, but I wouldn't think that fact would be very significant at car speeds. So I assume the real culprit is that combustion is less efficient. But why? > Recently, we've had some real temperature swings in our area, with > several days in the 30's followed by several days in the 50's, and so [quoted text clipped - 6 lines] > would be very significant at car speeds. So I assume the real culprit > is that combustion is less efficient. But why? 1. It takes more energy to heat cold air than warm air. 2. The engine has to run longer to bring itself and the catalytic converter up to their correct operating temperatures. >> Recently, we've had some real temperature swings in our area, with >> several days in the 30's followed by several days in the 50's, and so [quoted text clipped - 11 lines] > 2. The engine has to run longer to bring itself and the catalytic > converter up to their correct operating temperatures. Yes, but these aren't the only two factors. I think you are both right. I've observed a reduction in mileage during cold weather after my converter is hot and after my interior is warm while at a speed that keeps the ICE running full time. One trip I take periodically involved a 120 mile round trip on I29 in the red river valley of North Dakota, the planet's flattest expanse of land. In the summer I can lock my car at 55 mph when wind isn't a factor and achieve a perfectly flat series of five minute bars at 53 mpg. In the winter the same trip yields a perfectly flat series at 51 mpg. I've repeated this several times. Overall mileage drops more due to the two factors you mention but I believe the 2 mpg difference doesn't involve these factors. > >> Recently, we've had some real temperature swings in our area, with > >> several days in the 30's followed by several days in the 50's, and so [quoted text clipped - 23 lines] > factors you mention but I believe the 2 mpg difference doesn't involve these > factors. Point (1) above did not refer mostly to heating air inside the passenger compartment. A much larger factor is the air used inside the engine cylinders. The expanding mixture of heated air and combustion gases make the car go. When the engine intake air is colder it takes more energy to heat it and do the necessary work of moving the pistons. Yes, winter gas reduces MPGs. Yes, colder air is denser, and yes, the Prius burns more gas just to keep itself warm; but the mere fact that the engine is a *heat* engine means that colder inlet air will require more fuel to make it produce the same power. I'm not sure to what extent the ideal gas laws apply to air in your tires, but the cold will reduce the pressure in them. This makes it difficult to inflate them properly. Also at start up the batteries are cold and electrical acceleration is much lower than normally. I'm in Alexandria, Virignia and have been getting around 36-42 mpg but I see it picking up with the warmer weather. One of the things I find very noticeable now is whether a trip is net uphill or downhill. When I come in to work it is clearly net downhill and I get stretches of 80+ mpg coasting down the hill on I-395 at 50-60 mph. I pay for it somewhat on the way back home but usually the car is warmer because it spends the day in underground parking. I have put STP Fuel Treatment in it once, but afterwards got worried it would not do the fuel bladder any good. Does anyone have informed comments on Fuel Injector Cleaner and the fuel bladder? > I'm not sure to what extent the ideal gas laws apply to air in your > tires, but the cold will reduce the pressure in them. This makes it > difficult to inflate them properly. Also at start up the batteries are > cold and electrical acceleration is much lower than normally. D'ohh!! Yes, tire pressure makes a noticeable difference. It should be checked monthly, or whenever the average daily temperature changes much more than 10'F. > I have put STP Fuel Treatment in it once, but afterwards got worried it > would not do the fuel bladder any good. Does anyone have informed > comments on Fuel Injector Cleaner and the fuel bladder? No :-) |
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