MPG in the Rain?

I don't know if you have summer and winter gas blends in CA, but we do in AL. I see my MPG drop about 1.5 MPG every winter. I don't know how much of this is due to the cooler temperatures and how much is due to the winter gas blend.

 

The energy recuction between the summer and winter blend is less than 2%. Pretty much undetectable by tracking mileage so something else is happening.

 

This is from the Government, so it must be right.

I have a 15 mile drive to work, so I probably fall under their short-trip category. 3, 4, 6 (& possibly 5) probably don't have much effect for me, so I'm guessing 1,2 & 7 are the main culprits.

Fuel Economy in Cold Weather

Cold weather and winter driving conditions can reduce your fuel economy significantly.

Fuel economy tests show that, in short-trip city driving, a conventional gasoline car's gas mileage is about 12% lower at 20°F than it would be at 77°F. It can drop as much as 22% for very short trips (3 to 4 miles).

Why is winter fuel economy lower?

Cold weather affects your vehicle in more ways than you might expect:

1. Engine and transmission friction increases in cold temperatures due to cold engine oil and other drive-line fluids.
2. It takes longer for your engine to reach its most fuel-efficient temperature. This affects shorter trips more, since your car spends more of your trip at less-than-optimal temperatures.
3. Heated seats, window defrosters, and heater fans use additional power.
4. Warming up your vehicle before you start your trip lowers your fuel economy—idling gets 0 miles per gallon.
5. Colder air is denser, increasing aerodynamic drag on your vehicle, especially at highway speeds.
6. Tire pressure decreases in colder temperatures, increasing rolling resistance.
7. Winter grades of gasoline can have slightly less energy per gallon than summer blends.
8. Battery performance decreases in cold weather, making it harder for your alternator to keep your battery charged. This also affects the performance of the regenerative braking system on hybrids.

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CA has winter fuel.

 

AFAIK its a Fed requirement and applies to all fifty states. Maybe there is a waiver for places like southern Florida? Would make sense for places like San Diego too.