Possible undiscovered performance and MPG issues with Prius v (lowercase v)

Just wanted to chime in here as this page came up on my search for my 2012 Prius V is averaging 31 mpg at the moment, best ever all year being 36 mpg. This is one of the first batches of the Prius V, our family bought it the first year of its release. I can relate to the "pulling trailer" sensation, the car definitely feels like it is being pulled back, a sort of "phantom braking" if you will. I can't tell what it could be. I lifted the car to spin the wheels and front two spin freely, rear spins as freely as any other rear wheel would (parking brake just touches it so it's not like a bicycle wheel, about one revolution and it stops). I am motivated to find out what the cause for this could be, it's really a head scratcher. All tests in Torque app are green, new spark plugs, no apparent issues. It's a mystery.

 

Are you sure the fronts "spin freely"? Is this maybe with car on and in Neutral?

The rear brakes on the Prius v are a little different than regular 3rd (or 4th) gen Prius: they have an integrated mini-drum brake, for the parking function. I don't have the repair manual for Prius v, but with a short-term Tech Info subscription you should be able to scoop the brake info. There's likely a procedure for checking proper operation of the parking brake, adjusting if needed.

FWIW, with my 3rd gen Prius, albeit with a different parking brake system, with a good push the rear wheels will spin 2~3 revolutions.

Maybe not that much difference?

 

The Prius v has a different 'drum parking brake' integrated into the disk rotors in the rear than standard gen3s. So it could be an issue.

The typical mpg problems are a low capacity hv battery that is not storing and returning enough power to assist the gas engine. This can easily cost four mpg. A really bad 12v battery can cause an excessive charge current that can waste mpg. This is far less common as most 12v batteries just fail to hold voltage. Wheel bearings can cause a drag when worn and will not exhibit the typical looseness. They will howl at speeds around 35-50 mph until increasing road noise drowns them out. Rear hub bearings on the v are becoming more common as higher miles accumulate. Deduct another four mpg for one bad bearing.

Extremely poor gas octane will decrease mpg while higher octane will slightly increase mpg. However Premium or ethanol free gas is not worth the increased cost. But substandard regular is not worth it. Just because a Costco gas is a low price does not mean its bad. Most gas in a given area comes from one to three refineries by pipeline with only locally injected detergent additives making the marketing difference. Sometimes the worst refiners will cheat a bit on octane.

Driving habits are a significant factor as well. If you have a light foot on initial acceleration, anticipate stops to maximize regen, let off slightly when going downhill rather than gaining speed and stay below 65 mph most of the time, the epa mpg of 42 for a v is possible. Just yesterday I averaged 45 mpg displayed on a hundred mile trip heading north to Austin on a 65 mph freeway. Returning on a parallel 85mph tollway would easily reduce mpg to 36 for that leg. And cost $6 for tolls. Lifetime displayed mpg is 41.5 over 250k miles, some with a failing hv battery and a worn bearing.

What you often find on these forums are satisfied users with low miles and early maintenance schedules. Others like me rolled 30k miles a year for the first eight years and experienced many issues others are just reading about. With 250k miles on the odo, mpg is something that matters to me. Its about the only reason I still have this car.

 

Thank you Mendel, you make a good point. I will have to double check the front wheel and exactly how freely they spin if at all, in park it certainly wouldn't spin (my memory recall isn't too great!). The rear wheels give some resistance, there is an adjuster on the rear brakes that moves the shoes closer or away from the drum. I will have to play with readjusting it, perhaps a notch or two looser, it is possible it is sitting too close to the drum at the moment.

Thanks for the video, now this is a wonderful reference. From the sound, if I'm not mistaken, I could hear the parking brake is just lightly touching the drum. I'll have to give this a shot tomorrow and see just how many revolutions the rear wheels spin with a strong push. This could explain the "pulling a trailer" feeling I have with my car.

It's almost 10 years on the original 12v battery, and "cold" voltage is 12.2v according to the vehicle reading, sounds like it's worth replacing anyways, and I'd consider it a blessing if it does address the mpg issue!

 

2013 v
290,000 miles 44...45 mpg
front tires 42
back 38
Michelin Defenders

 

Hey, I hear ya my friend. I posted about the same thing. I have a gen4 Prius that the 1st 80,000+ miles maintained 50+mpg (up through a Friday several months ago) then suddenly Saturday morning till now it’s dropped below 40mpg. Nothing has changed, especially overnight except the lowered mpg.

I’ve had similar comments claiming I don’t listen either…. As you know it’s not that, brakes, heat, etc… aren’t bad things to look into (& I do appreciate the help) but I believe there are several of us that has stumbled onto something wrong with the computer in the Prius. Not sure the dealers can even help. Anyways, I’ll keep following if you find anything out let us know and I’ll do the same. Hang in there. And finally I wanted you to know it’s not just the Prius v.

 

ah, the dreaded trailer prius, i remember that debate.

 

anything new on this?

 

PTTR!

 

I fixed my trailer Prius.
My economy went from a normal 42 to 35 overnight. I went through all the maintenance cleanings... egr, intake manifold, fuel injectors, tire pressure... Then I checked the fuel pressure... It was 30 psi and should be 40 to 50 psi. It was off enough to effect MPG but it still ran and started normally. I first changed the fuel regulator and no change, so I went to the actual pump. I went through one tank at 44 MPG and then my headgasket blew. Talk about an emotional rollercoaster ride. My JDM Gen 4 engine is to arrive in 4 days. Wish me luck.

 

Oh no! You have just started the excessive fuel pressure causes hg fails theory. Get Mendel on board and it will be accepted quickly.

 

To be fair, my #1 had started missing rarely a few months ago. I moved coils and plugs around and problem stopped. I did notice that the #1 spark plug was "cleaner" than the others so I was starting to worry.

I LOVE you guys, I am fairly new to this forum and have been cramming on putting in Gen 4 ICE. So many have been helpful.

 

Every trailer has its own reasons.
Every non-trailer does not have these reasons.