Gas mileage keeps dropping

I'm not sure if the gas companies switch to a winter fuel blend in CA, but, if they do this could account for your MPG drop. Also, do you use top tier gas regularly? As far as the loud noise, I think I would have it checked out. Hopefully your dealer is conscientious. I'm extremely lucky, my mid-MI dealer seems very honest and concerned with customer satisfaction, not all dealers are the same.

 

check your tyre pressures.

 

The car is most likely fine. You have a different driving pattern than the EPA test so you shouldn't expect to get the EPA ratings exactly. If you drive more freeway then expect to get lower mpg.

And yes, California does switch to winter blend fuel.

As for the noise, you don't happen to start the car to move it a few feet or from the street into the garage often do you? That often causes a horrible noise upon starting the car again,.

 

Where does the loud noise come from, and what does it sound like? Is the battery vent behind your driver's seat blocked?

 

Time for new batteries.

 

On a brand new 2014 Prius C... why is this your go to response? Car is slow, get new batteries. Car is making a knocking noise... get new batteries.

 

itz been about a month now @msp4 since your original post. i have noticed that when i drive my son to school in the morning the first half mile or so i get only 16 mpg or less. yes less. itz the car warming up in the morning etc. ,,, keep in mind that not every trip to the corner market is going to be 50mpg. please drive and enjoy. and when your buddies ask just pretend evvery trip is 83mpg like mine.

 

My gas mileage has steadily been dropping after being constant for the first two months (September and October).
I was getting 50-53 mpg for the first two months after purchasing the car, and then once November hit, my mpg has dropped from to 47 for the next two fillups, and then 45 for my last fillup.

This coincided with the weather getting cold (I live in the Washington DC area), so I'm assuming that the decrease in mpg is due to the engine taking longer to warm up. Does the air temperature affect tire pressure as well? Is it possible that I need to boost the air pressure in my tires?

45mpg is still pretty good (especially since I don't have the patience to accelerate slowly to maximize fuel efficiency), but I am hoping that when warmer weather comes again in a few months it will go back up to 50+mpg. Will it do this on its own? Is it okay to wait until the 5000 mile tuneup to put more air in the tires, or should I be doing that more frequently?

 

Click my Fuelly link to see how winter hurt my mileage when I was driving a ton last year.

 

Haven't been a car owner for very long, have you ?

Yes and yes.
In 3 months, you should have checked the pressure at least once; preferable 3 times regardless of weather changes.
The pressures have dropped with the drop in temperature.
When the weather goes from cold to hot, the pressure will go UP some.

 

Do you use the Eco button on or off.