9- 10 mpg loss conundrum

Discussion in 'Gen 2 Prius Main Forum' started by Sharnold, Nov 2, 2019.

  1. Sharnold

    Sharnold Member

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    2007 prius 168k miles. New tires, new filters, fresh oil change, new plugs and coil packs, no DTCs, and HV battery good. Only oddity I've noticed is the accessories plug going in and out on voltage while driving. I'm beginning to lean towards pulling the 12 volt and load testing it to check for bad cells. As you drive the car the ICE is spending more time charging the HV battery than the HV battery putting power to the cvt hence the HV battery is staying at a full charge. Any theories and words of wisdom other than my own deductions will be appreciated

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    #1 Sharnold, Nov 2, 2019
    Last edited: Nov 2, 2019
  2. Sharnold

    Sharnold Member

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  3. Sharnold

    Sharnold Member

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    Bingo after running techstream after a 30min drive and shutting the car down the battery with the accessories and headlights on only has 11.15 volts but with the vehicle running in maintenance mode the HV battery checks out perfectly but the 12 volt is only charging up to 13.86 after 10min of run time. These little 12 volt batteries are the devil on these cars 20191102_064121.jpeg 20191102_064434.jpeg 20191102_064232.jpeg

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  4. Classic Car Guy

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    Hi there,
    I'm no expert but we have the same car and I can see you definitely lost some mpg on your car. There is a guy here Patrick Wong I always ask him whenever I want to know something about my car.
     
  5. DMC-5180

    DMC-5180 Active Member

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    Have you ever replaced the 12V batt in the past?
     
  6. Sharnold

    Sharnold Member

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    I'm a mechanic and work on the prius cars. Everything checks out other than the 12 volt after load testing it on the bench it drops from 11 volts to 10.2. That plus the 32° mornings we have had plus his 40 mile commute equals horrible milage.

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  7. Classic Car Guy

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    No wonder why my car is eating a bit of gas this fall going winter. What is that gadget you're using and how do you use it?
     
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  8. Sharnold

    Sharnold Member

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    Toyota techstream will scan your car and give you live numbers on the whole car and allow you to run live tests and read all the DTCs
    I'm using a snap on battery tester to do a load test on the battery
    Also you must figure on tire pressure and how much you run your heater.
    A block heater is also a good edition to winter to help with faster warmups to save mpg

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  9. Classic Car Guy

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    okay sounds will try that unit.
    on the heater block are talking about the swimming pool worm?
     
  10. Sharnold

    Sharnold Member

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    The swimming pool what?

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  11. Classic Car Guy

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    Lol.. I mean noodles. I though someone was putting these in the front of their air dam to rum the engine warmer of cold seasons.

    [​IMG]
     
  12. DMC-5180

    DMC-5180 Active Member

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    Adjustments.jpg

    The air inlet block will , in theory, help slow down the radiator cooling some. The biggest demand item, and what cause the engine to run more in winter is using the heater. The HVAC is always trying to maintain cabin temp. This means it’s constantly asking the engine to run more.

    Pre heating the block will will mean the engine warms quicker and have easier starts especially in sub-zero F days. From a driving perspective, the air block with be more beneficial for winter mileage.
     
  13. TMR-JWAP

    TMR-JWAP Senior Member

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    So …….a block heater is $75...that's over 30 gallons of gas at my location..I would have to save (30g x 50mpg)...1500 miles for it to pay for itself.

    If I assumed I could get a 3mpg increase during the cold months, I would need to burn 500 gallons of gas. That would be 25000 miles. At 1200 miles a month.....for say 3 cold months a year,,,3600 miles …..7 years to get even without including cost to operate it...assuming it doesn't fail in that 7 year period. That's a long payback period.

    I agree, the airflow blocker @ about $3 sounds like a better deal.
     
  14. EternalPrius

    EternalPrius New Member

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    the 12v creates all sorts of havoc on these, so much more frustrating than on a regular vehicle. also, bad gas/e85/high ethanol content will make this happen too. happened to me once on my 05.

    As you know a bad 12v battery can take with it the charging system and some accessories. Since there is no 'alternator', it can infect the charging apparatus, the CVT system. My 12v batt took down my HV water pump I'm suspecting. If the HV water pump isn't pulling strong enough, you will not get any codes and not realize anything is wrong. make sure it is functioning. it will only throw a code once the cvt overheats substantially! and it can cause the system to gimp itself to prevent overheating. feel it with your hand to make sure it's humming along. it will charge the hv and 12v batt erratically, gimp your ac, do all sorts of weird stuff I can't even think of right now.

    even if the 12v voltage is fine while cold it can still cause problems. My battery was doing weird things to the generator/electrical system, it tested fine with a volt meter but bad at 300 cranking amps
     
    #14 EternalPrius, Nov 2, 2019
    Last edited: Nov 2, 2019
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  15. DMC-5180

    DMC-5180 Active Member

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    It’s a car, their is no pay back, period!Just cost of ownership.

    Last winter I wish I would’ve had a block heater on my car. We had 3 days in row where the Hi temps were mid -20’s F°

    I was starting the car every few hours to keep some warmth in it. A couple of the starts were after a 6 hours. They were so hard on it, that it caused it to throw DTC codes for cam position sensor out of time.
     
  16. Classic Car Guy

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    That's a good thought. Yes it could be useful in some areas like north on Indiana to north side. Im just new to hybrid thou I know some about older cars. One thing for sure it helps the engine run better as always on a normal operating temperature. I'm a bit more concern about the wear and tear of the engine. I have an 80's Toyota pickup and 60's Austin Healey. I had both cars for a very long time. I hardly even lose any oil on it on regular driving days. I always take atleast min of 2 mins or more before I roll to work. Good thing I have the prius now and its my everyday point a to b car.
    and Good thing I don't need the block heater since I live in the northwest.. if I'm correct.
     
  17. DMC-5180

    DMC-5180 Active Member

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    If you live in the northwest and rare experience temps below zero F. You don’t need a block heater. Upper Midwest like me, it can get extremely cold in January/February.
     
  18. Classic Car Guy

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    Far out! I miss the Delorean days! Every Thursday the fresh recycler magazine comes out and were always in the used car section. Triumph, Jensen Healey, Austin, MG, old Jaguars, Sunbeam and so on... Name it and you have the car the next day. Very nice and intact! Nowadays I don't know what they're trying to sell. besides the car looks like it got raped and rotisserie'd the price is a moon shot.
    Well once a month I see a DMC-12 on the road and as much as I like them and I know I cant touch those.
     
  19. DMC-5180

    DMC-5180 Active Member

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    I’ve had mine 25.5 years. Long time enthusiast.
     
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