I spent an hour bleeding the radiator and still the cabin air is cold

Discussion in 'Gen 2 Prius Technical Discussion' started by andy song, Jan 27, 2026 at 10:50 PM.

  1. andy song

    andy song Junior Member

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    My 2008 prius was loosing coolant and we got a new radiator and water pump as it has 320k miles so we figured it was time

    Put the car into maintenance mode and turned the heat all the way up to max in the cabin and started filling it up with coolant

    2 bottles (1 gallon jugs) later the cabin air is still cold

    I would say I waited almost an hour

    I kept pouring in coolant into the radiator cap as the level dropped

    Sometimes it will bubble up and pour out and then it would drop and I would fill it back up

    The thermostat was also replaced BTW

    Any ideas what I am doing wrong?
     
    #1 andy song, Jan 27, 2026 at 10:50 PM
  2. BiomedO1

    BiomedO1 Senior Member

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    You should probably check your heater water pump and heater control valve (3-way switch valve) and I believe you have a coolant bleed valve on a 2008 Prius. Follow OEM procedures and independently verify that coolant is moving where is suppose to. Just feel the external hose temperatures to verify flow.

     
    #2 BiomedO1, Jan 27, 2026 at 11:09 PM
  3. pasadena_commut

    pasadena_commut Senior Member

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    Did the coolant loop ever stop bubbling? If not it isn't full.

    The capacity of the entire loop is 9.1 quarts. Normally on a drain and refill only about 6 quarts come out, but perhaps you drained more because of the water pump/thermostat/radiator? Did you measure the amount that came out?

    Car was losing coolant, was there an obvious leak? If not there could be a blown head gasket and the missing coolant is going out the tail pipe, and exhaust fumes may comprise some of the bubbles that are being observed. That isn't a common failure mode on this generation, but it does happen. Also the OP notes 320K miles, and at that age what is "normal" for cars under 200K may not always apply. The 2nd generation head gasket typically lasts over 250K miles, but I don't think anybody here expects one to last forever.
     
    #3 pasadena_commut, Jan 29, 2026 at 8:20 PM
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