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  1. #1

    Temperature effect on milages makes no sense

    The setup: 2006 HCH-II, ~50,000 km on it (35,000 miles), perfect service, winter tires. I drive 65km to work (50 miles), 40-45 of them hiway.

    Monday morning, sunny and warm, around 3 degrees (38 f). Drive to work and easily get ~5.2 l/100km (45 mpg). Storm comes in during the day, temperature falls to 3 below (28f). On the drive home I get 6.1 l/100km (39 mpg).

    So a change of about 6 degrees Celsius results in a 20% drop in fuel economy? Why? The car is fully warmed up 5 minutes into the 50 minute drive. What's going on?

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  3. #2

    If anything, a lower

    If anything, a lower temperature would produce better mileage. Lower temperatures produce better mileage due to a greater disparity between inlet temperature and combustion temperature.

    That temperature difference represents the total thermal potential from which your propulsion efficiency is derived.

    I suspect your difference in to/from-work mileage is a result of elevation change between endpoints and speed/driving variations. My wife experiences a 10-15% variation in mileage in her 20 mile commute between the outbound and return trips.

    Another factor can be humidity. Higher humidity can lower fuel economy as the mass of the inlet air is higher and energy is consumed in heating the additional mass during combustion.

    Also, if the roads were wet, your rolling friction would be higher.

  4. #3

    This is fairly consistent

    This is fairly consistent with Hybrids, A couple of things com to play the temperature drop makes smaller Oxygen molecules therefore you have more to mix to get a good burn, I know it sounds goofy but the larger warm air Molecules don't mean more to attach to the Oxygen. Then there is the need to run it a little harder to get it to running temperature, I have found that 65-75F I get the best mileage. And yes we can be smug about it too hey we are still getting 40+ MPG most of the year. I do agree about ther humodity to some extent, there was a device called a water injector that when injected into the air stream of the inlet it cooled the combustion chamber allowing a better burn.

  5. #4

    How do you know the

    How do you know the difference in mpg is due to temperature? It could be that your house sits on a higher elevation than your work, in which case you would be driving uphill to get home, hence the lower mpg. A better test would be to pick one route, either to work or from work, then record the mpg on 2 different days for that same route.

    That said, I have noticed significant drops in mpg on my Civic Hybrid the colder it gets. I actually get better mileage on hot summer days with the A/C running than on the coldest winter days. The sweet spot for mileage seems to be around 65-75 F as the previous poster mentioned.

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