Low MPG on Prius?

unless you're flooring it all the time, doing 80+ all highway or live in the rockies, i would have the dealer check it. that's why you buy certified, right?

 

There are lots of possibilities, so we need more information and clues before guiding you in a useful direction. So please start by reading this, and answering as much of it as possible in this thread:
Fuel economy complaints/queries? Please copy, paste & answer these questions, esp. if you're new

 

Obviously, there are many reasons it may be performing poorly.

One reason may be a nearly dead 12 volt battery. In a 'normal' car you would know it was almost dead by the "Ur ur ur" noise it makes when starting the engine, but in a Prius it only starts the computers, the HV Battery starts the engine, so you may have a dead 5 year old 12 volt battery and not know it.

One simple way to test this is by trying to use the power windows before you turn the car on, but there is a more accurate way as well:
Weird stuff happening? MPGs dropping? Test The Battery | PriusChat

Another 'Prius" issue that can hinder performance is a dirty throttle body:
TB cleaning

 

There are many varieties of Goodyear Vivas, so it is hard to make a blanket statement, but the Federal S657 tires are not Low Rolling Resistance tires. When you need to swap tires, much better LLR tires are available, you may get an extra 2 MPG with them.
Low Rolling Resistance replacement tires: Current List | PriusChat

In addition, while Toyota's specified tire pressure is optimal for a comfortable ride, some of us here on Prius chat think higher pressures provide more load carrying, safer handling, and improved MPGs. It is hard to watch your tire wear over the internet but 40 PSI in Front/38 PSI in Back may be a good starting point. Lower from there if you need more comfort, or the center of the tire wears more then the edge You can go up (NEVER exceed the max load printed on the tire itself) if the edges wear faster than the center, and comfort is not an issue.

 

start checking your tire pressures regularly, and making sure they're where they should be.

 

your first tank was from the dealer and you're on your second tank?

 

We'd like to see actual battery voltages. But as long as you did your own checking, and are not trusting the shop on this (shop tests are notorious for saying the Prius 12V is good when it isn't), it is likely OK.

Numerous drivers start seeing 12V battery problems at about 4 years, but nearly all of this happens at the chilly start of winter, not the middle of a hot summer.

Did you reset both Trip meters since buying the car, so that you are seeing only your own performance not skewed by the previous driver?

Are you resetting one Trip meter every morning, to provide more rapid feedback about your own MPG performance? This is a great learning tool. It also highlights the warmup penalty for short trips and the better results of longer segments.

Short trips hurt MPG due to engine warmup. This is true of all cars (except electrics, which the regular Prius is not). This is very noticeable at 5 miles, but much less so at 15 miles. It is also bad on regular cars, but most drivers don't know it because they don't have an MPG gauge staring them in the face.

By itself, stop-and-go should not hurt much in a Prius if you can mostly glide to the stops. Racing to stops then braking hard, beyond the regeneration limits (watch the CHG bar of the HSI display) will hurt. Unfortunately, the race-and-brake style is expected or even forced in some driving cultures.

However, lots of stop & sit time combined with heavy AC use will slash MPG. The car must power the AC full time, moving or not.

See the other replies concerning Low Rolling Resistance tires. These models will likely hurt a bit. And if either set is new, it will temporarily hurt a bit more, as all new tires do.

The TPMS warning on the dash is not sensitive enough for MPG use, only for warning of potentially catastrophic underinflation. And it anyone reset it while pressure was low, the pressure will have to fall extra low before any warning pops up.

Get a tire gauge and get actual pressure measurements.

Please keep us updated with your performance and with new clues. This is a learning process. I wish someone could have told me the real methods to get good MPG thirty years earlier. The common drive-gently advice is seriously oversimplified.

 

Top two bars are green, you have more charge than the car really wants, it will do EV when it can.
The middle 6 bars are blue, the car has the charge it expects.
The Bottom two bars are pink/purple, battery is low, expect sluggish acceleration.

 

John,

Did you have a chance to check out your tire pressures? Your original reported mileage is ridiculously low, which would indicate that maybe you have multiple things going on.

Certainly non LRR tires will cause a hit. Underinflated tires will greatly decrease mileage as well. But even if you addressed these two items and added 7 mpg back to your average, 40 mpg is awfully low. It will be a long time before you'd ever see any type of alignment issue revealing itself on the tires. I suppose if you get new tires for the car, check out if they can do an alignment as well.

I'm not sure how you would check this (others would know) but you might want to ensure that your brakes aren't dragging.

You don't have anything like a bike rack or a storage bin on top of the car do you?

Good luck and thank you for following up on this thread. Please continue doing so.

 

I just remembered that I'm speaking of Gen3 (2010+) trip meters, and don't recall whether or not your older model has two of them, or just one.