Setting water pump belt tension question

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by pasadena_commut, Feb 21, 2026 at 7:35 PM.

  1. pasadena_commut

    pasadena_commut Senior Member

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    Out of curiosity, if one were to loosen the tension bolt for that belt by exactly N turns (whatever it takes to remove the belt), swap on the new belt, and then turn that bolt the other way exactly the same amount, would the belt be at the correct tension? Naively it seems like it would, at least as long as nobody ever readjusted the tension after the previous belt was put on.
     
    #1 pasadena_commut, Feb 21, 2026 at 7:35 PM
  2. PriusCamper

    PriusCamper Senior Member

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    That's how they do it on spacewalks outside the spacestation... They have two different people at ground control to help count your rotations too. Of course when not in the vacumm of space you get dirt and grime and belt wear which can slightly change the number of rotations you need. Also a brand new belt will stretch a little and so a tiny bit tighter would be better than a tiny bit looser.
     
    #2 PriusCamper, Feb 21, 2026 at 8:42 PM
  3. BiomedO1

    BiomedO1 Senior Member

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    The short answer is NO. The old belt is worn and stretched and your assuming the new belt is within millimeters of length of your old belt. Tension the replacement belt per OEM manual/procedures. Don't over-tighten them or your going to have bearing and bushing issues.
     
    #3 BiomedO1, Feb 21, 2026 at 8:42 PM
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  4. pasadena_commut

    pasadena_commut Senior Member

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    I'm assuming that nobody ever adjusted the tension on the current belt after it was installed. If that assumption is false it was probably (re)adjusted shortly after the initial installation. Is it common to readjust the tension on this belt on this car in that manner? I have no memory on any of the cars I have owned of a mechanic ever adjusting a belt tension (except when replacing a belt), and I'm certain I never did it myself.
     
    #4 pasadena_commut, Feb 22, 2026 at 1:40 PM
  5. ChapmanF

    ChapmanF Senior Member

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    I wonder what the manufacturing tolerance is on the length from one new belt to another.

    I'd probably just set the tension per the instructions and move on to life's next question.
     
    #5 ChapmanF, Feb 22, 2026 at 1:51 PM
  6. pasadena_commut

    pasadena_commut Senior Member

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    #6 pasadena_commut, Feb 22, 2026 at 1:59 PM
  7. Mendel Leisk

    Mendel Leisk MMX GEN III

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    #7 Mendel Leisk, Feb 22, 2026 at 2:18 PM
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