Why are coolant maintenance schedules different?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by PriusII&C, Aug 29, 2025 at 6:43 PM.

Tags:
  1. PriusII&C

    PriusII&C Active Member

    Joined:
    Oct 15, 2013
    416
    136
    0
    Location:
    San Jose, California
    Vehicle:
    2012 Prius
    Model:
    II
    Toyota Prius 2012 Warranty & Maintenance Guide booklet: on page 51, footnote #3，it says "Initial engine coolant replacement at 100,000 miles/120 months... Initial inverter coolant replacement at 150,000 miles/180 months."

    Why the difference? I suspect the inverter operation temperature is lower than the engine, but not sure if that is the case.

    If temperature, in addition to time, affects coolant life, then the less one drives, the less degradation the coolant. For a person driving 5k miles a year, maybe he can safely delay the first engine coolant replacement from 10 years (only 50k miles) to somewhere later, like 12 years (at 60k miles)?

    Please share your thoughts.
     
    #1 PriusII&C, Aug 29, 2025 at 6:43 PM
  2. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    112,887
    51,370
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    because of the head gasket problem, it is advised by some to change the engine coolant more frequently, and test in between.
     
    #2 bisco, Aug 29, 2025 at 8:56 PM
    Grit and Georgina Rudkus like this.
  3. Mendel Leisk

    Mendel Leisk MMX GEN III

    Joined:
    Oct 17, 2010
    59,343
    40,828
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    Worth noting too: beyond the initial changes, Toyota USA specs subsequent changes for both at 50k miles or 5 years, whichever comes first.

    FWIW, Toyota Canada specs 160k kms (roughly 100k miles) or 10 years as the first change, for both. Except they didn’t fix the decal on the inverter coolant reservoir: it says don’t change till 150k… miles. :confused:
     
    #3 Mendel Leisk, Aug 29, 2025 at 9:21 PM
  4. Georgina Rudkus

    Georgina Rudkus Senior Member

    Joined:
    Sep 15, 2018
    3,368
    2,358
    0
    Location:
    Taylors, SC
    Vehicle:
    2012 Prius v wagon
    Model:
    Two
    If the coolant becomes acidic, it will likely degrade the synthetic rubber lining of the head gasket. It's not the steel in the head gasket that leaks.

    Coolant is cheap. Head gasket repair and associated connecting rod, rod bearing and engine block damage from a broken connecting rod through the side of the block can be very expensive.
     
    #4 Georgina Rudkus, Aug 29, 2025 at 9:41 PM
    Grit likes this.
  5. Grit

    Grit Senior Member

    Joined:
    Aug 22, 2017
    6,535
    4,218
    1
    Location:
    Wilkes Land
    Vehicle:
    2012 Prius
    Model:
    Four
    Definitely wrong car purchased if driving 5,000 miles a year. With turd gen hv bat at 10 years old, you be better off with a gasser climate changing car.
     
    #5 Grit, Aug 30, 2025 at 12:44 AM
(You must log in or sign up to post here.)