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Prius Mileage decrease

I bought a 2012 Prius new and averaged just under 53 miles per gallon for the first 15,000 miles regularly. I have a long commute so my driving mix of city/highway is pretty consistent. When starting the car one morning there was a fairly loud series of clicking sounds from the engine compartment, which then stopped. From that point forward the mileage has dropped to just under 50 mpg. Same driving habits. I am bringing the car if for it’s 20,000 mile check up shortly. Any ideas if something happened to the battery I should ask about? It is still under warranty.
Thanks for your help.

Perhaps someone put the wrong oil in when changing the oil? Make sure you have the right oil in the engine and see if it gets any better.

Also check your tire pressure.

A drop from 53 to 49 MPG really isn’t that much. It might be a matter of your gas station using winter mix fuel, which California recently did due to a fuel shortage created by the shut-down of a refinery.

I have never got that great of mileage in my 2008. The tire pressure and the air filter being changed does make a difference, but I wish I got the mileage you do!

What part of the country are you in, the cold weather can account for much of that drop !

A drop from 53 mpg to 50 mpg, as measured by the car’s own computer is insignificant. There is nothing wrong with your car.

There have been several valid suggestions: winter fuel, temperature drop, tire pressure. Together these factors may account for the difference.