Suggestions for 33 MPG Improvement

Discussion in 'Gen 3 Prius Fuel Economy' started by normythebear, Jun 19, 2020.

  1. normythebear

    normythebear New Member

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    I have a 2012 Prius 5 with the advanced tech package. I'll first mention the obvious mods that reduce fuel mileage:
    All-weather tire diameter increased from 205 to 215/55R-17 Vredestein Quatrac 5 XL
    30mm Spring spacers to stop bottoming out on Boston roads.

    I've had the car for about 1 year. However, even prior to the mods a few months ago, I still averaged only about 35mpg computer calculated. It's bad regardless of outside temperature.
    Tire pressure is always about 44psi.
    Oil is 0W-20 synthetic.
    Had an alignment 6 months ago.
    Mixed highway/city
    Gentle driving habits with anticipatory driving
    Setting on "Eco"
    Generally empty vehicle
    Mostly flat terrain
    Use mostly whatever fuel costs the least.
    No warning lights on dash
    Engine feels fine with no obvious misfires or sounds
    New brakes, so no issues with dragging.

    Is there anything obvious I'm missing? I'm mechanically adept and able to do my own work, but I don't want to start throwing parts and money at it.
     
  2. fuzzy1

    fuzzy1 Senior Member

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    Are you adjusting the math for the diameter change? Remember that increased diameter means that the true distance traveled is larger than displayed on the odometer. And the same thing happens to speed, you're going faster than in an unmodified Prius at the same speedometer display, and higher speeds also reduce MPG.
     
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  3. ASRDogman

    ASRDogman Senior Member

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    Have you cleaned the egr system?
     
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  4. bisco

    bisco cookie crumbler

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    how many miles on her? could be so many things

    what was the average before dropping, or has it been 35 since you purchased?

    do you know the cars maintenance and accident history?
     
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  5. ttou68

    ttou68 Member

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    You may want to consider a new set of struts and shocks if you are bottoming out considering the age( and I'm assuming the mileage) of your Prius..

    And ditto on tire size..
    You may want to check this website, to compare your current tire size and factory..

    Tire Size Calculator
    Tire Size Calculator

    There are many causes for poor MPG... EGR, PCV, Intake Manifold and sensors could be full of oil from PCV, spark plugs, weak but not failed 12V battery, dirty fuel injectors etc....


    Posted via the PriusChat mobile app.
     
    #5 ttou68, Jun 19, 2020
    Last edited: Jun 19, 2020
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  6. Mendel Leisk

    Mendel Leisk Senior Member

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    Comparing revs-per-mile with Michelin Primacy in 215/45R17:

    upload_2020-6-19_7-58-3.png

    Comparing to to Michelin Premier in 195/65R15 (a little closer):

    upload_2020-6-19_8-16-41.png

    Not likely a factor, but that's going to give harsh ride, hard on suspension too?
     
    #6 Mendel Leisk, Jun 19, 2020
    Last edited: Jun 19, 2020
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  7. normythebear

    normythebear New Member

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    Thanks for the replies! I did consider that the mpg calculator would be a bit off due to the larger tire diameter. MPH wise, I'm usually about 3 mph off at highway speeds when I compare the GPS to the speedometer. I replace the shocks/struts when I installed the spacers and did the brakes.

    It has about 170k miles on it. I think the windshield has been replaced but there's no obvious indication of accidents, other than the passenger-side wheel well cover is missing, suggesting the bumper might have been off in the past for a fender-bender. The car tracks straight, so I don't think it was serious. It looks like the windshield has been replaced because it annoyingly has "frit" where the Advanced Tech Package camera is, whereas the stock windshield doesn't. I'm unsure about maintenance history prior to me, which was about 20k miles ago.

    I'm at 34 mpg the past 1000 miles (computer calculated), but prior to the larger diameter tires, it was about 36, which is still pretty bad. It did drop after getting those tires, but seems to have stabilized. Also, the air filter is new, which I forgot to mention and would affect gas mileage.

    So, suggestions are clean EGR, clean PCV, clean intake manifold, clean sensors, check 12v battery voltage, check fuel injectors, replace spark plugs. I could also check individual cell performance on the traction battery. I could do all this pretty quickly and inexpensively. Would coil packs affect mpg? I wouldn't want to buy them if they're still good since that's expensive.
    Any other suggestions?
     
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  8. Johnny Cakes

    Johnny Cakes Active Member

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    For a long time, I was getting about 35 MPH and was amazed by the people who consistently got around 50 MPH. Like you, I thought maybe something was wrong with my car, but even 35 MPH seemed pretty good compared to my last car.

    Then I watched the video below about "pulse and glide," proper use of the display, and a few other "tricks." This video is a sticky in the mileage sub-forum.

    It basically becomes a video game, but I can routinely get near 50 MPH using the simple tips in the video -- and without driving nuts or causing a safety issue by doing weird stuff. Now I'm amazed by the people who get 60+ MPG on the highway -- I'm waiting for that video.

     
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  9. normythebear

    normythebear New Member

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    Thank you for sharing. Though, if there is nothing wrong with my car, I'd be disappointed that I have to adopt a new driving style just to get the EPA mpg estimate. I'm still mostly happy with the Prius overall.
     
  10. ASRDogman

    ASRDogman Senior Member

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    As with ANY motor vehicle, if you want to get more MPG's, you'll need to change your current habit.
    Same principle if you want to lose weight. You'll need to change your eating and exercise habit.

    But, you do not have to change anything. But if you decide you want better mileage, you don't have to
    make a huge change. Even minor ones would improve the mpg's.


     
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  11. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    It's not like you're changing your name and joining the Navy, you just have to watch a video and drive different for a couple of hours in order to see some results. It might show you that your car isn't working right, and then you'll have a little more info for fixing it. Personally I don't think that's it, your driving style would have to be atrocious before it made that much of an impact. On the other hand, Cambridge...

    The tire size you're describing sounds quite big for a Prius. I know some versions of the Prius can waste fuel trying to top up a worn-out 12v battery, anyone check on that yet? What about aero profile, any racks, deflectors or gutter covers out there in the wind?

    Minor correction: air filter does not affect fuel consumption in fuel injected cars. The dirty filter/bad MPG thing is just for carburetors.
     
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  12. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

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    If you're running stock rims and they're costing you probably 2-3 MPG, real world over the 15s.
    The tires have already been addressed.


    "Tire pressure is always about 44psi." - Good. Probably gains you 1 maybe 2 MPG.

    "Oil is 0W-20 synthetic."
    - Stock. No effect. I've been using 5w30 for 100,000 miles and I'm around 45MPG real world.

    "Had an alignment 6 months ago." -
    Good to know. In bean town you should probably have gotten the lifetime package.

    "Mixed highway/city"
    - What's the mix? The city driving is hurting you more than anything else except perhaps the engine.

    "Gentile Driving"
    - In BOSTON?!?! Yeah, right.That's probably B.S. since you've not mentioned any rear-end damage from people ramming you during those "gentle starts".....but we'll leave that aside for a minute.

    "Setting on Eco"
    - meh. Power mode makes no more power in this vehicle, so Eco isn't going to move the needle much either.

    "Generally empty vehicle"
    - Check....mine always has about 100-200# of gear and some empty water bottles and gedunk wrappers.

    "Mostly flat terrain" - Check. East of the Rockies it's all mostly flat.

    "Use mostly whatever fuel costs the least." - Me too.....Doesn't matter.

    "No warning lights on dash" - yet.

    "Engine feels fine with no obvious misfires or sounds" - yet.

    "New brakes, so no issues with dragging". - Good to know.

    So.
    Here's the deal.
    My car gets between 40 and 45 (mostly 45) and I use my accelerator like an on/off switch, drive in Normal, and my beloved company puts very minimal maintenance in the thing.
    If you subtract a few MPG for those wheels you're dragging around, and 1 or two more for your environment (Bastan versus an undisclosed small southern city) we're probably hanging out in the same MPG neighborhood.

    Priuses are not magic.
    They're EFFICIENT.
    Any other ICE powered car that you drive might only get about 25 MPG.


    However (comma!) my Spidey senses tell me that you may want to investigate a couple of things because you probably should be closer to 40 MPG.

    1.) MAFS. - Throttle Body..........You can do the spray and pray method on the Mass Air Flow sensor, but I'd yank the Throttle body off and do a good clean and inspect.

    B.) The infamous EGR. @NutzAboutBolts had many excellent videos for maintaining G3 Priuses, and one of these will cover this. I know you said that you didn't want to Easter-egg the problem, but I'd throw an EGR valve at the car while I was in there.

    III.) Oil.
    It's not as much which flavor you use, but where it goes when you use it and how much is left over after 5,000 miles or so.
    Check it every other fill-up and make sure none of it is going anywhere besides your recycling center.
    Massachusetts in general and Bastan in particular tends to be a little 'handsy' with the rules and regs but hey......at least you're not California, right?
    Consider using an oil catch can.
    I'm thinking that they might let you do that there.


    Good Luck!
    Let us know if things improve! :D
     
    #12 ETC(SS), Jun 29, 2020
    Last edited: Jun 29, 2020
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  13. ASRDogman

    ASRDogman Senior Member

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    That's not quite correct. If the filter is dirty enough, the engine can't get enough air.
    So even though the mixture might be close enough, there isn't enough fuel or air to give
    enough power.
    But I've seem some pretty bad filters and the enough still ran decently.

     
  14. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    In a carbureted engine, the gas/air mixture is calibrated in advance assuming a clean air filter. A blocked filter increases the vacuum in the system, causing the mixture to be enriched outside of calibration limits.

    In a fuel injected engine, the engine gets whatever it gets through the filter. The air mass is measured after filtration, and the computer only allows enough fuel to properly burn the air that did make it in. This calibration is constantly being updated.

    So yes, you may lose out on the total air coming in, but the computer is always going to keep the mixture right where it should be. The result is that the engine loses output potential rather than MPG as with the carb car. If the filter is really choked, then you get very little power- and therefore even less opportunity to burn fuel.
     
  15. ASRDogman

    ASRDogman Senior Member

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    Yes, less power per spark, which will decrease power, and mpg. Because there will not be enough power
    to drive the engine to drive the car...
    As easy as it is to change and air filter, and inexpensive, no reason NOT to change it.
     
  16. Grit

    Grit Senior Member

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    There’s a person here who’s yet to charge their engine filter since new purchase. The person will remain anynoumous.
     
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  17. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

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    I haven't charged mine either. :D
     
  18. ASRDogman

    ASRDogman Senior Member

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    I bought a reusable one. Just wash it out and dry it. Simple.
    I've cleaned it once, bugs, leaf pieces, some dirt. Not bad.
    The one I changed out, was dirty. Thousands of miles on it...
     
  19. mjoo

    mjoo Senior Member

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    Air filters get more efficient at removing dirt the more their loaded with dirt. Also their restriction increases.

    I have a filter minder that tells me when the restriction becomes unbearable for the engine (link in sig). Until then I'll continue to use it and remove the bugs, leaves, etc.

    My reusable prefilter (not in sig ;)) does an excellent job at removing the large debris before it reaches the main air filter. And it's dirt cheap - a women's pantyhose sock :ROFLMAO: clamped to the inlet of the air filter box. It was a tip I got from bobistheoilguy.
     
    #19 mjoo, Jul 9, 2020 at 12:02 PM
    Last edited: Jul 9, 2020 at 12:12 PM
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