My 2015 Prius C is getting very low fuel mileage on the highway.

Discussion in 'Prius c Fuel Economy' started by Need4Camaro, May 8, 2020.

  1. Need4Camaro

    Need4Camaro New Member

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    On the street I can get between 42 and 45 MPG. On the highway Im only getting 32 - 35 MPG and tonight I only got 26 MPG. That is lower than my 2017 Camaro SS gets at 80 which is terrible... What could be going wrong with my Prius and what do I need to check?

    The 32 - 35 MPG figures happened at 70 MPH
    The 26 MPG figure happened at 80 MPH

    The weather was fairly cool outside. Infact I've noticed the colder it gets my mileage just plummets, as in you can literally watch the MPG go down while driving as it gets cooler outside. It seems to do its best fuel mileage on warm to hot days or above 80*F

    What seems to be going on?.
     
  2. bisco

    bisco cookie crumbler

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    those numbers may be correct at those speeds.

    the battery loves warmth to a point. when it gets too warm, you lose efficiency at the other end, and get more degradation. a/c use will counteract both
     
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  3. AlphaFox

    AlphaFox New Member

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    of you drive 80 expect poor milage
     
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  4. Aaron Vitolins

    Aaron Vitolins Senior Member

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    First of all, check your hybrid battery fan! The Prius C is known for collecting a lot of dust in the vent and fan. Second, check tire pressure, and 12v battery. 26 mpg at 80 is very bad for any Prius. Something does seem off. Start with the basics if you haven’t already.
     
  5. The Electric Me

    The Electric Me Go Speed Go!

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    I think the easiest thing to do, would be just reset a trip meter, and then go for a nice speed limit following hour drive on the freeway, and see what your MPG is reading.

    I do think those numbers are low.
    Washington State has sections of their highway at LEGAL speed limits of 70 mph. I use to drive my Prius on those stretches and the MPG was actually very, very good.
    32-35 mpg at 70 mph, I think could be indicative of a problem.

    But my first step would be a more relaxed, consistent highway drive, and seeing what MPG that returns.
     
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  6. sam spade 2

    sam spade 2 Senior Member

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    What you are seeing might be "normal" for that specific car......given it's age.
    At 80, it didn't get great mileage when new and now little things can have a BIG impact.
    For instance, did you have the windows open ?
    Have you checked the intake air filter lately ?
    Did you have a heavy load.....or going up hill.......or against a headwing ??

    A healthy dose of Techron wouldn't hurt.....but probably won't help either.

    You aren't putting "premium" fuel in it, are you ??
     
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  7. Pri3C

    Pri3C New Member

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    As far as regular hybrids are concerned, isn't the Prius c one of the best rated (if not the best) for gas mileage? Don't these models do even better the standard Prius? I'm driving between 60-75 on the highway, usually on cruise, and getting very good gas mileage on my 2014 with 47k miles. Last week I drove 70 for nearly 500 miles one day on hilly roads and got between 49-55mpg until the winds shifted the last 60 miles and the mpg dropped to 47ish.

    I think these numbers seem quite low.. as a new owner I would be disappointed.. but who knows what factors are contributing to it.
     
    #7 Pri3C, May 9, 2020
    Last edited: May 9, 2020
  8. rjdriver

    rjdriver Active Member

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    I wouldn't expect very good mileage at 80 mph. Based on the mileage I get with my 2012 C, something is probably wrong with your car. Unless your highway driving is loaded with hills and a constant headwind, you should be getting in the high 40s to low 50s at 70mph. If the roads are fairly level try using cruise control on your next highway trip and see if that makes a difference. If mileage is similar with CC that at least elminates your driving technique as a factor. You'll always lose a few mpg in colder weather but not like what you're quoting.

    As Aaron mentioned, check the hybrid battery cooling fan to make sure the filter is not clogged, get your tire pressure somewhere between 36 and 44 depending on your desired comfort level. If you haven't had the car from new and have no record of maintenance done I would change the air filter ASAP. You don't mention how many miles are on the vehicle. If it's around or over 100,000, it's time for new plugs. If none of those things make a difference, have a mechanic you trust take a look at it.
     
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  9. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Something's up with this one.

    I'd never expect a great score driving at 80, but this just seems too low.

    Completely normal to see better mpg in warmer temps- the air density is reduced, and the computer is enforcing a constant AFR, so less fuel will be used and less power created.

    Check battery fan, check aero, check to make sure you don't have a dragging brake or other wheel-associated problem.

    Also verify the wheels and tires on the car- if somebody put a goofy aftermarket size on there, the math will be wrong for speedometer, odometer and MPG meter. They'll all lie.
     
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  10. kenoarto

    kenoarto Senior Member

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    Our 2005 Prius gets high high 40s at 55mph. It looses 1 mpg per mph above that. Mid 30s at 80+mph is normal (especially with wind and hills). Prius c does a little worse...
    Posted via the PriusChat mobile app.
     
  11. Pri3C

    Pri3C New Member

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    The 2015 Prius c should not do worse than your 2005 Prius. I think for me high crosswinds winds have had the biggest negative impact on my mpg so far. A lot of hills hasn’t really been a problem in the right conditions. I’ve kept my mpg in the 50s in hills going 70. It loves the downhills.
     
  12. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    You'd be surprised. The longer body of the regular Prius model gives it a noticeable aerodynamic advantage, seen as better MPG particularly at higher speeds.
     
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  13. Pri3C

    Pri3C New Member

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    Ok, fair enough. For the record, I would never expect great fuel economy at 80 MPH, and I think if someone plans on driving 80 a lot they picked the wrong vehicle. I thought I read something in my manual about not driving the c above 85 MPH for extended periods of time, so doing a lot of 80 MPH drives probably isn’t good for the car. But I’ve been cruising at 70 and still getting great results. Normally I drive 60 in 55 and 75 in 70, but I think I’ve decided to stick to around 70 on the interstates. Unless I need to pass someone or I’m in a big hurry, going 5-10 miles faster isn’t going to save me that much time and I’ll have a happier Prius in the long run.
     
  14. rjdriver

    rjdriver Active Member

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    Agreed. I have spent very few moments at 80 in my C, had to be in a real hurry to do those, and found them all very unpleasant due to high road and wind noise. In a prior life I was a type A driver and it would often take speeds of 90 or better to get me out of the high speed lane. I was just beginning to grow out of that type of driving when I got the Prius, which quickly taught me how foolish, dangerous, and wasteful it all was. I now bow down to the Prius gods in thanks.
     
  15. topshot

    topshot Member

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    If that 70 is using cruise vs you're guessing at an avg without cruise then I'd agree your MPG is bad. I took my new-to-me 2015 Prius c Three on a road trip as soon as I got it and got 44-45 MPG doing 74 with cruise, which was on I-75 and 40 in the hills of KY and TN. Wind can knock off a few MPG.

    ICE are more efficient when warm so MPG goes down some when it is cooler (i.e., takes more heat to warm up the engine and keep it warm on cold days) but I haven't found it to be anywhere near that drastic. The full-size Prius even has insulated underbody panels to help hold in the heat that the c lacks.
     
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