Mystery Coolant Leak 2012 Prius II

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by KeystoneKid, Jan 28, 2026 at 11:37 AM.

  1. KeystoneKid

    KeystoneKid Junior Member

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    Yesterday I noticed a small puddle of pink coolant on the garage floor under the aft wheel well on passenger side of car. Further inspection showed similar small puddles on the floor under the passenger side of car up to the front wheel well. I opened the hood and removed the bolts holding the reservoir and checked for any coolant under the reservoir. It was bone dry. The coolant level in the reservoir indicated it was full. No leaks at the small hose on the reservoir. (I drained and refilled the coolant a couple years ago along with inverter coolant and also changed the CVT fluid.)
    I removed the under engine panel to further inspect for leaks. Nothing found. Over night the garage floor shows no leaks anywhere. Now I'm at a loss to find this mystery leak. Anyone have any ideas where this coolant could be leaking from? Also this car is always parked inside my garage where temps are above freezing and not outdoors for long periods of time so I don't suspect a freezing issue. Thank you all in advance very much!
     
  2. Mendel Leisk

    Mendel Leisk MMX GEN III

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    Windshield washer fluid is also pink.
     
  3. KeystoneKid

    KeystoneKid Junior Member

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    Hi Mendel. In my case, I am using a winter blend windshield fluid that is blue. I will also remove the coolant reservoir cap to release any vacuum if it's present and see what happens. Just a thought. Thanks for your reply!
     
  4. Mendel Leisk

    Mendel Leisk MMX GEN III

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    Strange for coolant to be in vicinity of an aft wheel well. As far as I know, the Exhaust Heat Recovery system is the furthest back coolant should be, which is just a foot or two behind exhaust manifold. It's definitely pink? How does it feel, oily, just slick? Taste? Coolant would taste sort of sweet I think. Regarding toxicity, if you just taste with finger to tongue, then rinse with water, I think you'd be fine. :)
     
  5. PriusCamper

    PriusCamper Senior Member

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    Any noticeable performance issues or warning lights? Does your exhaust pipe smell like coolant? Or is exhaust pipe wet?
     
  6. KeystoneKid

    KeystoneKid Junior Member

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    Yes no kidding, where coolant had dripped from the rear wheel well leaving a small puddle, you'd think I would easily find its source. Also had some small puddles as well all along the side of the car, on the floor, front to back. It is pink.
    I just drove the car long enough to get up to "normal" operating temp, pulled in the garage and looked the engine bay over as best I could and underneath it. No coolant that I could see. I thought perhaps it maybe leaking around the water pump, thermostat/inlet hose or ?? Noticed the coolant in the reservoir still cold. I thought it would be hot. Not sure if that's normal? Removed the reservoir cap with a psft sound Found no leaks. I didn't taste it but it smells like coolant (yesterdays puddles).
    I'll continue my small trips around home and see what happens. I did make an appointment at a local shop I know of for next Tuesday but may cancel if no further leaks. He wasn't overly excited about taking in a "hybrid" vehicle. That is usually the case around here outside of the dealership. Dealer won't help unless I bring it in to their shop. Thanks again for your replies!
     
    #6 KeystoneKid, Jan 28, 2026 at 3:58 PM
    Last edited: Jan 28, 2026 at 4:15 PM
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  7. rjparker

    rjparker Tu Humilde Sirviente

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    If its coolant from the reservoir to the rear wheel it could have started up front and flowed to the rear, especially if the garage floor has a slight slope.

    You have many connections up front on that side including the radiator (2), thermostat (2), water pump, passages through the timing chain cover and the reservoir (3).

    The reservoir pressure relief cap has been known to release toward the firewall and then close.

    I would monitor the coolant temperature with a scanner or obd2 device.

    If it is the head gasket then you have air in the system displacing the missing coolant. Often it ends up in the heater core.
     
  8. KeystoneKid

    KeystoneKid Junior Member

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    Thanks for your reply! First thing I thought was a bad water pump, thermostat, or heater core. I have no clue where they put that heater core but I did feel around the floor carpeting under the dashboard. Anyway I won't reinstall the engine under cover until I'm sure the leak is gone. That reminds me to pull the dipstick and look at that oil on it. So far it's a mystery.
     
  9. Brian1954

    Brian1954 Senior Member

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    I agree with what rjparker wrote, especially to monitor the coolant temperature.
     
  10. KeystoneKid

    KeystoneKid Junior Member

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    If the head gasket was blown wouldn't I see muddy looking oil on the dipstick? In other words coolant mixed in with the engine oil right? Thank you!
     
  11. KeystoneKid

    KeystoneKid Junior Member

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    I haven't noticed any performance issues. Only drove it a few miles Yesterday. Temp came up normally and heater temp worked OK. The outside temp was about 30 degrees Fahrenheit. No warning lights on dash. The exhaust pipe is dry and actually pretty clean. I have about 91,000 miles on the car. 2012 Prius II The oil on the dipstick is normal looking as I just did the 90K mile oil and filter change. I looked over the engine again this morning and do not see coolant leaking anywhere. Strange stuff I tell ya. I'm thinking I will have to take it to the dealer and have them check it out. That's a scary thought. Local shops are afraid of hybrids. Thank you for your reply!
     
  12. rjparker

    rjparker Tu Humilde Sirviente

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    This generation is known to slightly leak coolant from a coolant passage into the cylinder where it burns off during combustion. No coolant in the oil. In fact it usually is less than what you are reporting.

    A borescope test is the most reliable as combustion gasses in the coolant tests often give false negatives.

    One thing for sure - if you are losing coolant it will overheat sooner or later causing a head gasket issue.

    It would be prudent to find a hybrid experienced shop for various reasons. Even if you have to drive an hour.

    Car Care Nut HG Borescope at 660s



    South Main Auto
    Excellent Borescope Footage at 6:50
    Honda Misfires on Coldstart Only
     
    #12 rjparker, Jan 29, 2026 at 11:33 AM
    Last edited: Jan 29, 2026 at 11:39 AM
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  13. rjparker

    rjparker Tu Humilde Sirviente

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    Watching the coolant temperature is pretty easy with a low cost bluetooth elm327 obd2 interface and an app like "Car Scanner".

    If its getting hotter than 205f a bad water pump, clogged radiator or thermostat could cause pressure relief action at the reservoir.

    Image.jpeg
     

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    #13 rjparker, Jan 29, 2026 at 1:12 PM
    Last edited: Jan 29, 2026 at 1:24 PM
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