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2016 Prius Low MPG

Discussion in 'Gen 4 Prius Care, Maintenance and Troubleshooting' started by jyii07, Jun 16, 2022.

  1. jyii07

    jyii07 Junior Member

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    Hi All,

    I have a 2016 Prius 4 with around 120k miles. The avg mileage dropped from around 55mpg to around 48mpg the past couple months so I thought spark plugs were to blame. I got those replaced by the mechanic (purchased the OEM Denso ones), replaced the cabin/engine air filters, cleaned out the hybrid battery fan filter, and even inflated the tires. Is there anything else I'm missing that could contribute to the lower mpgs? Coolants were also drained and filled around the 105k mile mark. I was thinking of cleaning out the MAF sensor but wasn't sure if gen 4s required cleaning as often as the gen 3s. Should I go ahead and clean the MAF sensor anyway and see if that helps? Any other ideas?

    Thanks
     
    #1 jyii07, Jun 16, 2022
  2. bisco

    bisco cookie crumbler

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    Tires?

    a/c?

    any driving changes?

    alignment?

    12 volt battery?
     
    #2 bisco, Jun 16, 2022
    Last edited: Jun 16, 2022
  3. jyii07

    jyii07 Junior Member

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    Changed out two tires around 10k miles ago (no changes in MPG after the change). Driving habits are the exact same. Alignment looks fine. I'm in socal so a/c is always on but I don't see much of a difference when turning it off anyway. Would a low 12v battery affect mpg? Battery was last replaced 3 years/40k miles ago.
     
    #3 jyii07, Jun 16, 2022
    bisco likes this.
  4. jerrymildred

    jerrymildred Senior Member

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    Spark plugs were right on time even if they didn't help.

    Low 12V could drag down the mpg a little bit, but don't replace it as a means of troubleshooting; have a load test done.

    When's the last time you checked the brake caliper slide pins. They will eventually stick and cause the brakes to drag. This not only uses more gas, it wears out the pads & rotors prematurely.

    Looks like you covered everything else that I can think of right now.
     
    #4 jerrymildred, Jun 16, 2022
    Tande likes this.
  5. robsnyder20

    robsnyder20 Active Member

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    check tire air pressure. I don't think that would have such drastic impact on MPG. When I switched out my LRR tires to defenders, I probably lost 5-6 MPG initially but has come back up since after a few thousand miles. You could try charging the 12v battery if you have a somewhat good charger and see if that helps. Check fluid in 12v battery as well. I find when I fully charge my 12v I get slightly better MPG, nothing scientific but does appear to help. Good luck.
     
    #5 robsnyder20, Jun 16, 2022
  6. jyii07

    jyii07 Junior Member

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    A shop replaced all 4 rotors and brake pads at 115k miles and assume (maybe incorrectly?) that they lubed the caliper pins while replacing the rotors.


    Thanks.. ill just refill the tire pressure again. Will check 12v too.
     
    #6 jyii07, Jun 16, 2022
  7. bisco

    bisco cookie crumbler

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    i suppose new brakes would be a good culprit to take a hard look at. gen 3 had a specific method for rear pad installation, which was easy to mess up. idk about gen 4
     
    #7 bisco, Jun 16, 2022
  8. jerrymildred

    jerrymildred Senior Member

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    They should still be lubed, but not necessarily correctly installed, as @bisco mentioned.

    What happened that they had to be replaced so early? Road salt induced rust?
     
    #8 jerrymildred, Jun 17, 2022
  9. jyii07

    jyii07 Junior Member

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    hmm how would I check these specifically?
    Bought the car in NY, moved to socal and got them replaced here. Mechanics here aren't used to seeing that much rust and corrosion on the rotors and maybe they could've lasted longer but it cost me $600 to get it all replaced so I got it done anyway.
     
    #9 jyii07, Jun 17, 2022
    jerrymildred likes this.
  10. bisco

    bisco cookie crumbler

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    jack it up and see if they spin freely
     
    #10 bisco, Jun 17, 2022
    CR94, FuelMiser and jerrymildred like this.
  11. priusgto

    priusgto Active Member

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    Both times my 12v battery started to fail I noticed about a 5-6 MPG drop. It wasn't gradual, but something I saw within a week or two. Last time, I removed and charged the battery then load tested it which immediately dropped to 11v and showed weak. When I took it back to the parts store where I bought it they said it tested good but replaced it after I explained what was happening. The very next drive the MPGs were back up to normal.
     
    #11 priusgto, Jun 25, 2022
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