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2010 Prius Fuel Economy Puzzle

Discussion in 'Gen 3 Prius Fuel Economy' started by Dominique Pelkey, Jun 12, 2022.

  1. Dominique Pelkey

    Dominique Pelkey Junior Member

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    Hello.
    I have been reading through many threads to try to get to the bottom of my MPG loss.
    I have a 2010 with a newer motor in it (My car has 240k miles, but I think the engine is probably closer to 110k).
    I did recently have my brake actuator replaced, however, I feel like the real culprit could be my AC usage?
    It is really hot in Phoenix right now.

    I was usually getting around 42-47mpg in the cooler months (no AC usage).
    The past couple of weeks have been getting worse and worse. I was hovering around 37-38, but now I have gotten as low as 32mpg... I did recently get new tires, I think they are the OEM Bridgestones; I got a really good deal on them.

    I am a decent mechanic; do not know if I could do all the things you all do. Would there ever be an issue that all 4 tires are dragging? I only ask, because I did the rim test, and they all seemed pretty hot, but it is 115 degrees in AZ today!

    I guess I say all this to say... Where could I start? Should I change plugs first? I just removed my 12v battery, I am testing it now and letting the car "reset". Am I able to get a good idea on how bad the EGR system is without actually taking it all apart? Would my hybrid battery be getting weak, or does it really not operate in that fashion?

    Sorry for the long post, thanks for any insight.
     
    #1 Dominique Pelkey, Jun 12, 2022
  2. bisco

    bisco cookie crumbler

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    did you own it last summer? if so, how was the mileage?

    new tires usually drop mpg until broken in. pump them up a bit over spec, but not too high in that heat. what model bridgestone, are they LRR?

    you can check the wheel drag by jacking her up and spinning them, or get up to 30 mph on a flat road and throw her in neutral. she should pick up speed, and you can play with the brakes without regen interference.
    who swapped the engines? how many miles after it was installed did you start to see lower mpg's?

    is it the original hybrid battery? consider dr. prius app to run a health check.

    how old is the 12v? get a free load test at an auto parts store.

    are the air and cabin filters clean? intake and hybrid battery fan?

    oil level? tranny oil? have you cleaned the throttle body and maf sensor?

    have you cleaned the egr circuit?
     
    #2 bisco, Jun 12, 2022
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  3. jerrymildred

    jerrymildred Senior Member

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    I'm also wondering if this is your 1st summer with the car. The extra A/C load in the summer can be a real drag, especially if you're mostly low speed city driving. The slower you go, the higher the percentage of total power is spent on cooling the cabin.

    New tires, even LRR ones, will lower mileage till they break in. And non-LRR will keep it low. Could be as much as 5 mpg.

    Brakes dragging is another possibility. As @bisco said, get it up on jack stands and see how freely they spin.

    If the plugs haven't been changed twice, you're due right about now.

    A weak 12V can lower mileage, but I don't think it would be that much. Still, a good thing to check on.

    The 2nd Gen doesn't have an external EGR system that you can/must maintain. It's done internally through the valve timing. Does my Prius have an EGR system? | Page 2 | PriusChat (Thanks, @m.wynn!)
     
    #3 jerrymildred, Jun 12, 2022
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  4. bisco

    bisco cookie crumbler

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    the o/p is a bit confusing, but it is (supposedly) a 2010 with 240.000 miles, and a replacement engine with (allegedly) 110,000 miles on it.
     
    #4 bisco, Jun 12, 2022
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  5. jerrymildred

    jerrymildred Senior Member

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    Forgot about the replacement. Let me amend it to:
    :D
     
    #5 jerrymildred, Jun 12, 2022
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  6. abdullah arslan

    abdullah arslan Member

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    I ve 2010 @ 257k with original engines, with only city driving getting 55mpg currently, only highway gets 45 and combined 48-50.
    After I bought the car at 230k, replaced transmission fluid, spark plugs, ignition coils, 6 months oil cycle, all brake pads, rear rotors, ICE coolant, PCV valve, intake gasket, all filters, 2 tires,12V battery; installed OCC, windows tints, and cleaned intake unit.
    I know when dragging on rear wheels, it gets only 38 mpg, happened to me.
    Also bought a filter for traction battery vent from dealer
     
    #6 abdullah arslan, Jun 13, 2022
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  7. bisco

    bisco cookie crumbler

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    ?
     
    #7 bisco, Jun 13, 2022
  8. Mendel Leisk

    Mendel Leisk Senior Member

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    The easiest part of the EGR system to inspect is the pipe between the EGR valve and intake manifold. More info in video #16 here. That said, it's a virtual certainty your EGR system needs cleaning; see first link in my signature.

    Yes, could be a factor.

    Yes again, especially with short trips.

    Look into Dr Prius app.

    Have you had brake work done recently? The rear brakes are disk, with integrated parking brake function. The parking brake style requires specific orientation of the caliper piston. Misorientation pretty much guarantees drag. More info in my signature, second-to-last link.
     
    #8 Mendel Leisk, Jun 13, 2022
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  9. Dominique Pelkey

    Dominique Pelkey Junior Member

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    Hey everyone, I have been trying to step my maintenance up on my car with a lot of the recommendations you all have offered.

    I got into the EGR system yesterday and it was quite dirty. I did not get to clean it all out but I did clean the pipe and plan to pull it all apart next week. I also cleaned the throttle body.

    The 12V battery is good.

    The tires I have are the OEM Bridgestone EP422 (I think that's the number). They aren't anything special but I got a set for a good price.

    Both my filters are still clean, and I even got into the Hybrid fan and cleaned it out (it wasn't dirty at all).

    Now for the new info. I started the car today after cleaning what I could last night... The car sputtered a little and then started running fine. However, after I stopped and turned the car off, and then cranked it back up, the Check Hybrid System message came on. It now feels as though I have no hybrid assist at all. So I am not sure if this is coincidental, but it seems as though my hybrid battery is now faulty... And maybe that is why my MPG has taken such a big hit?

    Thank you all for all the help thus far!
     
    #9 Dominique Pelkey, Jun 16, 2022
  10. Dominique Pelkey

    Dominique Pelkey Junior Member

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    Hey bisco. I pretty much replied to all of this above.
    However, I did realize I did not touch on the oil level and tranny level.
    Oil level is fine, I was going to change the oil tomorrow.
    I feel the tranny fluid needs to be replaced.
    And I did not get to clean the MAF (I did not have MAF cleaner on hand).
    Going to order the Bluetooth OBD2 right now.
     
    #10 Dominique Pelkey, Jun 16, 2022
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  11. abdullah arslan

    abdullah arslan Member

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    It sounds correct, after checking the battery via Dr Prius, you may start shopping for a new battery or reconditioning cells depending on the result. Don't know the exact numbers but dealer will charge around 3k, or you may go with Li-ion packs sold about 2.2k with DIY installation
    https://projectlithium.com/products/prius-lithium-replacement-pack
     
    #11 abdullah arslan, Jun 21, 2022
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  12. Dominique Pelkey

    Dominique Pelkey Junior Member

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    Hey Mendel. I swear I recall you talking about how to check if my brakes are dragging... Must have been another post. How do I check this? Also, is there any easy way to know if your brake booster its starting to go? I recently had my replaced, but it was replaced with a used one... More a curiosity than anything on this.
     
    #12 Dominique Pelkey, Jul 19, 2022
  13. ChapmanF

    ChapmanF Senior Member

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    An easy test I use for dragging brakes is described here.
     
    #13 ChapmanF, Jul 19, 2022
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  14. Mendel Leisk

    Mendel Leisk Senior Member

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    There’s a link in my signature. If you’re on a phone turn it landscape to see signatures.
     
    #14 Mendel Leisk, Jul 19, 2022
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