Prius MPG Drop - Master checklist

Discussion in 'Gen 4 Prius Fuel Economy' started by deathmage, Nov 10, 2022.

  1. deathmage

    deathmage Junior Member

    Joined:
    Apr 23, 2017
    8
    3
    0
    Location:
    Los Angeles ca
    Vehicle:
    2017 Prius
    Model:
    Three
    At around 35k, my 2017 Prius MPG dropped from 60-65mpg to 47mpg. I've been into extreme car modification for decades and I thought this would be a simple fix. I live in Socal and the weather only fluctuates from 65-85 on average. I started with the simple fixes first - reflash the ecu, check the tire pressure. Nothing. Rubbed my chin and took it to a tire shop and got a rotation. Still no change in MPG. Ok.. so I took it up a notch. Replace the air filter with K&N.. nope. Replace the cabin filter.. nada. wth. Nothing installed on the exterior to create wind-drag. I was frustrated at this point and took it up another notch. Replace the 12v battery with a brand new one from the Toyota dealer. This is usually the last step for many and often times it fixes the issue. For me, still nothing. I didn't notice any difference in the frequency of engine kicking in. I believe in 'if you throw enough money at it, you can fix the problem.' So I went and replaced all 4 tires (my treads were at 20%, but had some cracks on the walls). This still didn't fix the issues. My last ditch effort was to clean the fuel injectors. Still didn't change anything. I swallowed my pride and started digging deep into the forums for answers at this point, but still couldn't find anything worth while. So exchanged it for a 2022 Prime XLE, lol. I work from home, so I'll be filling up around 5x times a year. With a $6.50 average gas price in socal, this is awesome. Here's a check list for MPG drop. for 90% of you, one of this will solve your issue. Order from simple to more aggressive.

    - Check Tire Pressure
    - Rotate tires
    - Temp drop or fluctuation?
    - Elevation change?
    - States with extreme weather - try thinner synthetic oil in the winter and thicker in the summer
    - disconnect the battery to have your ecu re learn your driving habit
    - Change air filter. Change cabin filter
    - Newly installed roof rack or other culprit of wind-drag
    - Change all 4 tires
    - Change the 12v battery (often times this fixes the issue)
    - Clean the fuel injectors (not using injector cleaning solutions, but having the shop clean it)

    desperate attempts
    - replace transmission oil (dirty oil can interfere with shifting)
    - clean or replace O2 and MAF sensors
    - change spark plugs.
    - clean throttle body

    very lastly, it can be your electronics, which isn't common.
     
  2. deathmage

    deathmage Junior Member

    Joined:
    Apr 23, 2017
    8
    3
    0
    Location:
    Los Angeles ca
    Vehicle:
    2017 Prius
    Model:
    Three
    Also, running AC will hurt MPG by 3-5, but not by 10+.
    There's a small possibility that my main battery was wearing out, but it only had 35k miles.
     
  3. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    101,981
    46,253
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    check for brake drag
     
    ColoradoBoo and Mendel Leisk like this.
  4. Mendel Leisk

    Mendel Leisk Patron saint of newly poured sidewalks

    Joined:
    Oct 17, 2010
    50,623
    35,970
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    And recent tire replacement, will get you every time...
     
    Louis19 likes this.
  5. ColoradoBoo

    ColoradoBoo Active Member

    Joined:
    Jul 19, 2019
    528
    372
    4
    Location:
    Monument, Colorado USA
    Vehicle:
    2017 Prius
    Model:
    Two
    Years ago, I asked a Toyota mechanic about using fuel injector cleaners in my vehicles. He said I don't have to worry about that if I use gasoline from "Top Tier" gas stations. There's one near me so, now, I only fill-up from there, even if their price is a bit higher (it usually isn't, though).

    This website helps you find Top Tier stations and there's even an APP for your phone you can download.
    https://stationfinder.toptiergas.com/
     
  6. Louis19

    Louis19 Active Member

    Joined:
    Feb 4, 2022
    130
    128
    0
    Location:
    Laval Québec Canada
    Vehicle:
    2022 Prius Prime
    Model:
    Upgrade
    Yep, you are right . Just changed my Écopia for 4 winter tires and steel wheel for winter (mandatory where I live for the 1 december) and got a 10% dip in my EV range.
     
    Mendel Leisk likes this.
Loading...