2008 Prius MPG dropping like a rock after new 12v battery and coolant pump change

Discussion in 'Gen 2 Prius Fuel Economy' started by Jon Good, Feb 28, 2023.

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  1. Jon Good

    Jon Good New Member

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    Hey guys- I have a frustrating mystery. I recently changed my inverter coolant pump and my MPG dropped slightly from 40 to 38.. and then two weeks ago I had a bad battery and bought a new one from O’Reillys and now the mileage is going down every day and it is currently around 28 mpg. I hooked up the ODB scanner and looked at the hybrid battery with the free version of Dr. Prius, seems to be working fine.. I also put in a new air filter.
    What do you think might be going on??
    Much thanks for any responses.
     
    #1 Jon Good, Feb 28, 2023
  2. ColoradoCrow

    ColoradoCrow Active Member

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    hmm. check your tire pressure. Also check and make sure you seated the new air filter correctly. Have you cleaned your throttle body or intake manifold? How many miles on her? If you are 125K or more and original..it is time.
     
    #2 ColoradoCrow, Mar 1, 2023
  3. bisco

    bisco cookie crumbler

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    I think when you put in a new battery, the computers have to relearn everything.
    Track a couple tanks and let us know the actual mpg’s
     
    #3 bisco, Mar 1, 2023
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  4. Jon Good

    Jon Good New Member

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    I think that’s what’s happening but it has taken MULTIPLE tanks of gas, like you said, as it’s returning to 40mpg ish. I ran it on the freeway a few times at 60, resetting the dash counter and then it started creeping upwards again. thanks for the many responses I appreciate it!
     
    #4 Jon Good, Mar 1, 2023
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  5. edthefox5

    edthefox5 Senior Member

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    lol...the 12 volt battery has little to do with mpgs.
     
    #5 edthefox5, Mar 7, 2023
  6. Jon Good

    Jon Good New Member

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    Yeah I’m not sure what’s going on now because the mileage creeped up a little bit when I took it on the freeway it goes all the way up to like 47 mpg and then Intown drops like a rock down till like 30.. ugh.
    But all this started when I changed the inverter coolant pump and battery. Before I was getting a rock solid 40 mpg all the time.
     
    #6 Jon Good, Mar 7, 2023
  7. dolj

    dolj Senior Member

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    So which MPG meter are you specifically using?

    If it is the Average dispalyed on the Consumption screen (which is a lifetime since last reset), then the is a high chance that this was reset when you changed the battery.

    Depending on if you have ever pressed the "Reset" button on that screen then the average you saw before the battery change could be the average over many thousands of miles.

    With the average now reset, the average will be since the reset.

    The best way to know what is the true MPG is to calculate the true MPG by dividing the mile run on the cuurent tank by the numser of gallons you added the tank. Record the numbers in a biook (or better still create an account on fuelly.com) so you have a running record. When you fill up reset the Trip A and the average on the consumption screen. do the recording all over again at the next fill up. For this to work, you need to fill up completely, not partial fill ups.
     
    #7 dolj, Mar 8, 2023
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  8. Jon Good

    Jon Good New Member

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    Thanks for the answer I’ll try that and report back
     
    #8 Jon Good, Mar 8, 2023
  9. edthefox5

    edthefox5 Senior Member

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    You never stated the miles on the car or how long you have owned it?

    You need a new hybrid battery based on what your saying. if you just bought it you def need a new hybrid battery.

    Needs new hybrid battery is probably #1 reason people sell there G2.
     
    #9 edthefox5, Mar 10, 2023
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