2010 150k mileage dropping to 25MPG Help.

Discussion in 'Gen 3 Prius Main Forum' started by MarsMan, Mar 30, 2021.

  1. MarsMan

    MarsMan Junior Member

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    My milage has been dropping fast the past few months. Hoovering at 25 before servicing. No major changes in driving or weather. Los Angeles area. 3 weeks ago I did brakes and rotors it was just time, it wasnt to combat milage. But regardless, No change.

    Last weekend I did sparkplugs, PCV valve added an oil catch can, cleaned the throttle body. MAF. And intake. Cleaned the 3 EGR components, Pipe, valve and cooler. Changed the oil Mobile 1 0-20 high milage synthetic, changed engine and inverter coolant. The milage went up to 42 for a few days, now tanked back down to 28 today.

    I had a few under a minute engine hot dummy light kick on, cooled and turned off before I could even pull over safely, it happened today even after the EGR system cleaning, So I am ordering a new water pump and thermostat.

    I dont see any OBDII codes in torque even for the over heating issues. Im gonna test the 12 aux battery and traction battery with dr prius and see what I can find.

    Shes running good, though seems a little sluggish, not as peppy as before. No engine shake or knocks. Smooth as silk. Just my milage sucks nice person. Wheel bearings all seem good when I did my brakes.

    I am flippin stumped. Help.
    More info from more OBDII testing incoming.
     
  2. bettergolf

    bettergolf Active Member

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    Could be your hybrid battery failing. Do you notice the battery charge indicator being more active lately, meaning showing larger movements down and up the scale? Sluggish would also fit that as the battery wouldn't be helping the engine as well as it should.
     
  3. PriusCamper

    PriusCamper Senior Member

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    How about tire pressure and spark plugs... How are those?
     
  4. MarsMan

    MarsMan Junior Member

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    42/40 on TP and just chamged the plugs. NKG itridiums.
     
  5. MarsMan

    MarsMan Junior Member

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    Seems pretty normal. Nothing catching my attention. Did a Dr Prius battery test and it came out at 55.39% life. All tests were good. No ECU errors or anything else.
     
  6. MarsMan

    MarsMan Junior Member

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    Dr prius said traction battery is at 55.33% fair condition. No errors in ECU. 12v battery seems ok too need to get it fully charged and test again later playing with torque and dr prius for an hour it showed low at 11.1v but charging at 13.7. But I was going in and out of maintenance mode a lot so I was really punishing the 12v with head lights. Dome lights on off a lot.

    I am so freakin stumped..
     

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  7. Mendel Leisk

    Mendel Leisk Sand Pounder

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    Mpg drop came before brakework, if I’m reading right? Nevertheless, just for giggles: raise the rear and check wheels spin semi-freely?
     
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  8. Grit

    Grit Senior Member

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    o_O
     
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  9. PriusCamper

    PriusCamper Senior Member

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    Maybe you got a clogged cat? How many miles does it have on it? Any chance an oil change place consistently used too much oil in its early years?
     
  10. MarsMan

    MarsMan Junior Member

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    150k. I did have some oil burning, a quart every oil change or two.

    No ECU errors or anything.

    Im stumped. Thinking about trying new fuel injectors.

    I passed smog in Dec. (California) asked if he saw any errors, said it was clean, no issues, smog results were perfect.
     
    #10 MarsMan, Apr 2, 2021
    Last edited: Apr 2, 2021
  11. MarsMan

    MarsMan Junior Member

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    Tested again after driving that night and it sitting over night it was at 12.5 in the morning.

    It was low cause I was having trouble getting in maintenence mode. Restarting over and over at night with headlights on and all that.

    Tested again before going to lunch 12.6

    12v seems fine.
     
  12. MarsMan

    MarsMan Junior Member

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    Will test that tonight. And report back.

    Im chanhing my water pump and thermostat today. Parts just arrived.

    Debating new fuel injectors, or at least pulling to see if they look like crap.

    I use seafoam in the gas tank every other oil change. They should be OK. If they look bad, Ill just replace em.

    Im really just grasping at straws.
     
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  13. sLick415

    sLick415 Member

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    Sounds like you're checking your 12v in the diagnosis menu? I wouldn't look at that. I found that to be highly inaccurate. Use a multimeter.

    Posted via the PriusChat mobile app.
     
  14. MarsMan

    MarsMan Junior Member

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    Yeah I was using in dash. Found a good spot to test under the hood in the fuse box, also tested on the battery itself. Dash shows 12.3. Showing 12.7 on my multimeter under hood and on the battery. Will test again in the morning letting it rest 12 hours and will report back.

    I was gonna do my water pump and thermostat tonight, but my coolant isnt here yet, will do that in the morning and then take it for a hard run on the freeway and see how it does. Funny I get pump and thermostat next day, but 2 days for coolant.

    If it sucks after a week, Im gonna try replacing the fuel injectors. Not sure if I can clean them. I may try pulling one and see first.
     
  15. MarsMan

    MarsMan Junior Member

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    Ok raised the back, both spin good, no noticable drag. Just compared to my neighbors newer prius, and about the same. Id say mine spin quieter actually. But I did just do the brakes.

    I hit the front and rear calipers with a laser temp and the front were slightly hotter than the back too, as I expected. Same with my neighbors.

    I need to clean my rims better. Hands got filthy spinning em. LOL. I spent more time cleaning the wheel wells and chassis than rims :/
     
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  16. MarsMan

    MarsMan Junior Member

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    Ok after water pump and thermostat change and a quick hard flooring bad hard driving Im up to 38mpg on a quick 40 mile surface street and freeway run. And I drove like a race car driver. LOL

    She runs and feels the same. I STILL think shes a little sluggish and hitting the power band in eco mode way too much. But its a better improvement in MPG anyways. I may do the fuel injectors if I dont get above 40.

    Im gonna driver her around for a week and see how it goes.

    12v holding 12.3 or higher overnight.

    Rear wheels spin good. Front not as much. But the brakes are a week old. Im monitoring it might clean and relube. do not know what else I can do.

    Tires still front 42 PSI rear 40 psi.

    Maf good. No ECU codes. NO error codes. Some odd reading incomplete from torque. Any ideas?
     

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  17. Mendel Leisk

    Mendel Leisk Sand Pounder

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    That’s totally to be expected.
     
  18. MarsMan

    MarsMan Junior Member

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    OK, hoovering in the 35MPG territory, on highway it jumps to 40s, more city driving is goes as low as 33.

    I will be doing fuel injectors after all, reading other reports that it helped others.

    Question, should I replace my coil packs? They seems pretty costly and only seem like a replace it if it is bad item.
     
  19. ChapmanF

    ChapmanF Senior Member

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    I would treat them as a replace-if-bad item.
     
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  20. Yaesu

    Yaesu Junior Member

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    Have you checked the engine coolant temperature after the vehicle has been run for a while? After replacing the thermostat and water pump the temp. should be within specs. (whatever that is). Have you done a cylinder compression check?
     
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