<VV> Fuel Milage in winter - only minor Corvair

[Rad Davis]

Mostly due to friction of one kind or another:

1) everything is colder.  Lubricants all through the driveline are all more 
viscous, which results in more energy lost shearing them until they warm 
up, which, of course, takes longer, because they are starting off colder.

2) the tires are also colder.  More energy is expended making them deform 
every revolution until they warm up, which takes a long time since they're 
thrashing through cold air.

3) the air around the car is colder, and denser.  It takes more energy to 
push a car through the cold, dense air.

4) the warm-up cycle takes longer.  Water pumpers, in particular, have to 
have really well-designed cooling systems to allow them to warm up at 
all.  The effective efficiency of a radiator (expressed as a proportionate 
delta T) is about 50% higher at 30 F than it is at 90 F, which means that 
water going back into the engine is nearly always very close to ambient, 
which is more than 100 F below regulated water jacket temperature.  And 
since it's cold, so you're running the heater, which usually bypasses the 
thermostat.

5) the energy density of winter-blend gasoline is lower.  It has to be made 
from lighter compounds to give it a high enough vapor pressure to burn in a 
cold engine.  These lighter compounds offer less energy per unit volume 
than the heavier ones used in summer blends.

6) there's more likely to be something on the road.  And when you push the 
tires through that something, you're applying energy to displace it from 
the contact patch.  Here in PA, I always get noticeably worse fuel economy 
during snowy weeks than I do in merely cold weeks.

7) The colder air does not burn fuel as efficiently (yes, it can make more 
power, but not as efficiently) as hotter air does.  Most FI engines don't 
have intake air preheating except to prevent throttle body icing.  Once the 
engine's up to operating temperature, this is less of an issue, but see 4) 
above.

8) are your tires at recommended pressure on the coldest day of the 
year?  Mine aren't.

That's a good start, anyway.  Jim Burkhard might have some insight here.

-Rad Davis


At 07:27 PM 11/30/2005 -0700, Bob Gilbert wrote:
>Hi,
>
>
>
>I can understand why a carburetored car like a Corvair would have lower
>mileage in the winter. The choke stays on creating a richer mixture et voila
>lower mileage - at least while the choke is on.
>
>
>
>But,
>
>
>
>a)       For a carburetored car after the choke is off and
>
>b)      for a modern fuel injected car
>
>
>
>would there be any difference in mileage between winter and summer, ignoring
>driving conditions for the moment?
>
>
>
>Curious about winter driving.
>
>
>
>Bob
>
>
>
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