2009 Prius progressive loss of mileage

There are a million variables but here are a few suggestions.Increase your tire pressure back up to 42 psi front / 40 rear. also have you rotated your tires? Changed your oil? Do you use cruise control to drive ? It will help with economy if you have not gotten a feel for your gas pedal. Check the voltage of your 12 v battery if it is low it will hurt fuel economy. Also lighten up on the gas pedal during acceleration the Prius has sweet spots that increase fuel economy. 1600 to 1800 rpm range seems to be a good starting point. I am sure I am forgetting a bunch but I will let others chime in to add to my suggestions. If you have further questions you can message me.

 

it's probably the commute. what was it when you were getting 45-50?

 

Once my prius is warmed up, I get about 50 MPG freeway and close to 80 when hypermiling on expressways in the bay area. Yesterday I tried real hard and actually got 62 MPG over a 35 mile stretch from Livermore to Santa Clara all on the freeway, but I was keeping it 60 MPH. If I go my usual 75, I only get 50.

However, if I only went 3 miles at a time to work and back, I'd only get about 25 MPG.

 

No. There's little to be done about it except to increase tire pressures (you can go to the max shown on the sidewall) and realize that any other car under the same conditions would get about 1/2 the MPGs.

 

If you have A/C at max cold and you're only driving 3 mile commutes then your mileage doesn't seem extraordinary. Another thing to look at is whether your dealer overfills the oil which will impact your mpg.

At what free way speeds and distances do you get 45 mpg?

Florida is as flat as it gets so if you could get on the interstate and drive for 20 miles one way and 20 miles back at a speed of 60 mph, at 38 psi and without A/C you should get no less than 50 mpg.

Also wait for about 50 s before you start your journey to give your engine a chance to warm up and run through its cycling. After 50 s or so, the car will shudder, the engine will turn itself off and your trip's mpg will increase as you won't be depleting your battery by driving your car during these first 50 seconds.


If you're really worried you should make sure you car's engine gets into stage 4 and that your traction battery doesn't appear to charge/discharge way too fast.

 

OP: Are you resetting the mileage on the MFD, or do you just leave it to track long-term trends? If the former, it's a little odd. If the latter, then your symptoms match perfectly with having started a commute that will definitely get you lousy mileage. In that case I don't think there's anything at all wrong with the car. Mileage on short trips just isn't as impressive as on long trips.

 

if you have dropped from 42-45 to 36mpg under almost the exact same conditions, i would check your 12v battery, tire pressure, oil level, can't think of anything else, but something is not right.

 

I have a similar commute- just under 4 miles each way and my mileage stinks cause it is just too short. I have young kids so there is a fair bit of other driving - I have over 50,000 miles on my 2009 - and my mileage is in the right range on longer drives.

So, my guess is it is just the commute. When looking at your mileage when it is such a small sample that I think you just need to let it go. As long as the car is performing as expected on longer trips where you are getting a better read on actual mileage you should be all set.