Decreasing fuel efficiency in Prius

I have a 2009 Prius, which i bought in June. Initially i was getting about 51 mpg. The mpg has gradually deceased to about 43.

The tire pressure decreased some as the weather turned cold. i inflated the tires up to recommended pressure.

i tired higher grade fuel for one tank, which increased my mpgs by about 2-3.

I asked the dealer. He said it was probably because the ethanol level in the fuel has been increased due to winter. (i live in Ohio).

Does this sound reasonable? Should i be looking at something else?

Very common issue. The clean air fuel mix will change your economy some. Poor air pressure even more. The engine also runs more due to the increase in use of heat, wipers, lights are on more etc.

It’s your first winter, and you are still getting much better mileage that almost everyone. Wait until Spring and see if your mileage improves. I know that doesn’t help you now, but you have to show the dealer that something is wrong before he can convince Toyota to help you.

I believe the '09 Prius uses electricity to power the AC compressor so the motor doesn’t have to run to keep the car cool. However in the winter if you want heat then the gas motor turns on to provide heat to the cabin. You also are using headlights more and the rear window defroster uses a lot of current all of which will discharge the battery faster and turn on the gas motor.

Basically you can expect to get less mpg in the cold winter months. The blend of gas can also impact the mpg.

Yes, hybrids are known for getting (comparatively) poor mileage in cold weather.

My mom’s Fusion hybrid has lost about 4-5 MPG as the weather has cooled.

Just be happy that you’re still getting better mileage than virtually any other four-wheeled motor vehicle out there, and await warmer weather.

Winter gas has a slightly lower BTU/gal number, due largely to lighter HC “fractions” included in the fuel to boost vapor pressure.

I don’t believe you got better MPG using a “higher grade of fuel.” Octane rating does not indicate fuel energy content.

I do believe fuel selection is very important to a Prius. My 2007 Prius likes ethanol-free fuel for a 5% to 10% (yes, up to 5 MPG) improvement. Yes, I know thats not supposed to happen but real world experience (and having logged every fuel purchase for 27k miles) is worth more than an ethanol apologist’s “science”.

Also, it is hard to fill a pre-2010 Prius fuel tank the same twice in a row due to kissing up to the EPA’s dreamers by using a bladder in the tank. Deleted for 2010, and never used in the rest of the world.

Also consider wheel alignment. The Prius rolls very easily and just a bit of misalignment can eliminate that.

You didn’t say anything about tires and wheels. Hopefully you haven’t “upgraded” those. The car rides a bit bumpy but most find 40 PSI in the front and 38 in the rear results in an acceptable ride, better MPG, and more even tire wear for longer tire life than Toyota’s 35/33 specification.

I don’t believe you got better MPG using a “higher grade of fuel.”

I believe it, but I think the fuel was not the cause. I think it was a coincidence caused by other variables other than fuel octane.

UncleTurbo, even if the AC compressor uses electrical power, that power has to be generated by the gas engine unless you are getting a lot of power from the regenerative brakes.

It’s the stiff tires and lubricants plus a much higher electrical load. Everybody’s fuel mileage decreases in the winter…