From 48mpg average to 43 mpg average.

Discussion in 'Gen 4 Prius Fuel Economy' started by Priushappyguy, Aug 8, 2021.

  1. Priushappyguy

    Priushappyguy New Member

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    So in preparing for a trip from NE Kansas to Colorado, I changed the oil in my Prius, using full synthetic 0-20W and the Walmart oil filter. I also shook out the engine air filter, and we were off! At the time I had been averaging 47-48mpg driving my Prius like a sports car, it didn’t matter how I drove it, or the temperature outside, it just always would get at least 47, sometimes as high as 53 (averages). That all changed after I changed the oil myself, during the trip to and from Denver the car averaged 41mpg, and so as soon as I got back in town I called my local Toyota dealership, telling them that I changed the oil myself, and somehow the Walmart oil (super tech) has really hurt my gas mileage. They sorta shrug it off, and tell me (uh well you’re not due for al oil change) I persisted and requested they give me the same oil and filter they give all the other Priuses (to get the cursed Walmart oil/filter out of it) (ps I didn’t overfill, in fact I slightly under-filled at 4.3quarts, to account for the fact there was probably still a slight amount of oil sitting around in the engine) I’ve had quite a few Priuses, and my last one 2012 had started burning oil, I think it’s probably from people over filling the oil that starts the issue. Anyway, I take it to Toyota, they change the oil with their stuff, and 4 hours later my car is ready. Unfortunately this did not solve the problem, I continued to top out at 43mpg averages, with many trips averaging 39mpg (the Prius really likes that number when it’s not feeling well). Anywho, I recently replaced the engine air filter, and it helped, it’s back to 46mpg average, perhaps some of the dust from when I shook it out got into the air intake sensor. (When I changed it I noticed some debris on the area the seal goes on, perhaps allowing some air through the sides?) So I’m back up to 45-46mpg tank averages, however 48mpg is no where to be found. This happened right at 103k miles. The car runs fantastic, it’s just the gas mileage. Any tips before I go replacing transmission fluid/spark plugs/fuel injectors? Thanks!
     
  2. BellevilleMXZ

    BellevilleMXZ Junior Member

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    Spark plug condition?
     
  3. bisco

    bisco cookie crumbler

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    tires pressure?

    12v health?

    do you check the oil level with the dip stick?
     
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  4. FuelMiser

    FuelMiser Senior Member

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    A Gen 4 should never see mpg with '4' in the first digit! Road trips, i.e., sustained highway, is not what Prius is made for and you'll get lower mpg regardless. I'd say your best bet is examine your tires and tire pressures. A good quality low rolling resistance tire inflated over the recommended placard psi will do a lot for mpg.

    Does a 2016 Prius 2 have NiMH battery or Li-ion? NiMH will degrade faster than Li-Ion resulting in lower MPG. Your car is going on 6 years and 100K miles, so battery degradation could be affecting your MPG. Do you watch your SOC and/or energy flow? Does your ICE spend a lot of time recharging the Traction Battery? You'll lose a lot of MPG if the ICE has to recharge the battery a lot of the time.
     
  5. sam spade 2

    sam spade 2 Senior Member

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    My tip: STOP obsessing over 1 MPG.

    Whatever method you are using to come up with that number does NOT have resolution that is that good.

    Tapping the air filter probably forced some dust into the tiny holes in the filter material and caused it to be partially plugged.
     
  6. Colorado Boo

    Colorado Boo Member

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    It's normal for the mpg's to drop as the car ages. Many things can impact the mileage, as already stated. At 100,000, has the air intake manifold ever been cleaned out? You're also getting to the time when new spark plugs are due. (Lots of fake ones out there, even on Amazon, buy them at the dealer or have the dealer swap out your plugs if you don't want to do it...it's not expensive for a Prius.) Always use OEM parts when you can, stay away from Walmart auto center!!
     
  7. audiodave

    audiodave Active Member

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    2mpg off isn't much. Run some injector cleaner through the gas for a couple tanks. Check the wheel alignment.
    Posted via the PriusChat mobile app.
     
  8. Fubar XIII

    Fubar XIII New Member

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    Well, it seems appropriate that my first post (literally just signed up) should be about mpg.
    My experience has been much better, averaging just over 58/gal for the first 90k miles, running 55+ my last 85k. I'm in FL and tank to tank get 55-57 mpg in our (6 month long) summer and 60-65 mpg in the annoyingly brief, sub-75F winter (Jan-Mar).
    All that said, I ran into an issue of decreasing mpg early this year. No matter what I did, fuel cleaner, new plugs, new filters, different oils/filters, changing my driving style, etc., a steady drop into the upper 40s instead of the 60-65 I should have been getting based on temp, etc. Even a winter, rain-soaked, road trip to Detroit 4 months earlier (3200 miles, 51 mpg) was better.
    The problem ended up being a reduction in airflow thru the hybrid battery cooling duct work. An error message eventually showed up on the dash. A trip to the dealer, my first & only to date, rectified the situation for under $200. I'm back to 55-57 (in our low 90s highs, upper 70s lows) and expecting higher in the cooler months starting in Nov/Dec.
    I do see some slight variation from tank to tank, (bad gas, if it rains heavily/long, etc.) but consistently back where I was, never less than 54.x or higher than 57.x.
     
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  9. Fubar XIII

    Fubar XIII New Member

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    I've used Walmart branded oil repeatedly with no adverse outcome in any vehicle. As long as the oil meets the requirements (API SN, 0w20) specified by the manufacturer, who sells it, what name is on the jug, doesn't matter. (FYI, I used to work in the industry). Those numbers & letters are standards from the American Petroleum Institute - API - used throughout the industry to allow the consumer to compare apples to apples. Same as wear ratings on tires. I do an oil change for about $25 versus the $65-70 everyone around here charges. My time is worth $40.
    As for plugs, filters, coils, et cetera, I've been using the folks at RockAuto for nearly 20 years. The prices are amazing, shipping is fast, and if you should need to, returns are easy (only had to do that once). Assuming you are willing/capable to do the work yourself. Spark plug swap is not hard but requires removing the wiper blades & arms, a plastic panel & pulling out the coils first. Start to finish for me is about an hour.
     
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  10. Colorado Boo

    Colorado Boo Member

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    Yes, Fubar, I should've clarified about Walmart stuff...synthetic oil is fine there. I meant the Fram air and oil filters...I hate them! But I walked by the other day and was surprised my Walmart had OEM Toyota oil filters! I've never seen that. I'll have to stock up if they have the ones I use, save a trip the Yota parts guys.

    What vehicle do you have to remove the wipers to get to the plugs? My only vehicle I maintain that needs extra work for that is my daughter's 12 Sienna V-6...requires removing plastic and metal cowls and entire air intake manifold. (Which means I have to replace the gaskets in the manifold and the gasket on the throttle body...but I need to clean it out, anyway, so will kill two birds with one stone.)
     
  11. PosauneGuy

    PosauneGuy Member

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    In addition to Bisco's questions, I'd add gasoline to the list: E0 -> E10 -> E15?
     
  12. Fubar XIII

    Fubar XIII New Member

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    The Prius.
    You take off the wiper arms, remove the 3-part plastic shroud at the base of the windshield to access the coils which have the plugs under them. I've done it twice already.

    I'd say the same about the filters as the oil. Never seen any variation between brands, known or new. Use what you like, it's your car and your $$.
     
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