better mpg

Cold weather is a mileage killer for all cars, but driving a Prius brings it to your attention. There are four contributing factors:

1) Running the engine to make heat. This includes cabin heating, heating the engine itself, and heating the catalytic converter. Cabin heat is the only one you can control.

2) Winter blend gas. Many areas switch gas formulations in the winter, resulting in lower mileage. This is also something you can't control.

3) Increased friction. Cold weather and wet roads increase rolling friction. Cold air increases aerodynamic drag. This is yet another uncontrollable factor.

4) Low tire pressure. Dropping temperatures cause a decrease in tire pressure. This is something you can fix. Get out there and check those tire pressures.

Your only other options are to use grill blocking to reduce heat loss, and consider a block heater. Whether these make sense to you depends on your weather and driving habits.

Tom

 

You should check out the fuel economy forum topics and when you do you will see a bunch of posts about low MPG's and likely a sticky note at the top of the forum from Cwerdna about fuel mileage questionnaires.

Fuel economy complaints/queries? Please copy, paste & answer these questions, esp. if you're new

Why mileage gets worse in winter

(*edit - added links to two stickies at the top of the fuel economy subforum)

Long and short of it.....

It is cold. Your fuel mileage will decrease with the cold weather. The engine has a harder time maintaining optimal operating temperatures with the cold air blowing in and with you using the heater to further remove warm air from the engine compartment and place into the passenger compartment.

It is rainy/snowy. Your fuel mileage will decrease with inclimate weather as you will have to use extra gasoline to overcome the resistance they cause on the road.

Tire Air pressure. With the colder weather, your tire pressures will drop. Have your checked them recently? If not, please do so and add air as necessary. Your fuel mileage will improve if your tires are adequately filled. Myself, I fill to the max PSI in the front two tires (rated 44 psi for my tires) and Max PSI - 2 PSI for the rear tires (42 PSI). This matches the recommended difference for the Gen II (2 PSI higher in the front).

Winter blend gasoline does not have the same energy as summer blend gasoline.

The first 3 are the biggest components of lower mileage. Grill blocking will help immensely with the first issue as it can limit the amount of cold air coming into the engine bay, thus allowing for it to remain warmer. You can't do much about the weather. You can address any tire pressure issues.

If it makes you feel any better, you aren't alone in your observations. Your mileage will start coming back in the Spring and you will be singing its praises in the Summer and Fall again.

 

Colder weather affects hybrids more than other vehicles. Of particular significance is the warm-up time. As drivers who drive lots of shorter trips you'll see a bigger drop than other people, especially if you're also warming the car up before you leave. If you're not using one of your trip meters, I suggest that the next time you have a trip greater than 20 miles:
- reset the trip meter
- start your journey
- after about 10 miles note the mileage
- reset the trip meter
- after another 10 miles note the mileage.

You should see a significant difference between the mileage from cold and the mileage once warmed up.

 

By The Way, that "checkup" should include only the items required by Toyota. Otherwise the dealer will be selling you a couple of boat payments. See below for what's needed:
Toyota Parts and Service

 

In addition to all the above reasons my fuel economy is further reduced by heavy steel wheels and larger (195mm vs 185mm) cold temp tires. (ignorantly referred to as winter tires by most Americans, just as they call mild temp tires all seasons)

I don't mind the fuel economy hit this takes because winter is only 1 season, the prius cannot be rocked out of trouble (electric motor only reverse), people who risk accidents for higher mpgs are idiots, and nothing is more fun then driving past my neighbors all wheel drive audi stuck in deep snow.

 

I'm surprised no one has mentioned it yet but have your 12v battery checked. It should read at least 12.2v with the car off and no load. The original battery in your '04 is likely in need of replacement. That will cause mpg to drop. Combined with winter weather and fuel I could see you dropping into the 30s.