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Coolant keeps turning black

Discussion in 'Gen 4 Prius Care, Maintenance and Troubleshooting' started by William J, Mar 25, 2022.

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  1. William J

    William J New Member

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    Mar 25, 2022
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    2010 Prius
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    IV
    Recently bought a car 200k miles noticed coolant was black so I drained system 3 times. It has a cylinder 3 misfire and shakes in the morning. So I replaced the head gasket myself. Replaced the coolant now it's dark red. Still same misfire I changed spark plugs coils and injectors. Car also has no heat. Doesn't burn oil. Nothing looks milky coolant just turns black after driving around. Also when I checked piston heads they all look normal black color no discoloration. Old spark plugs look good no oil residue
     
    #1 William J, Mar 25, 2022
  2. dacoobob

    dacoobob Member

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    Four Touring
    I think your prius is haunted. Call an exorcist.
     
    #2 dacoobob, Mar 25, 2022
  3. jerrymildred

    jerrymildred Senior Member

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    I think it's usually cylinder #1 that has the head gasket failure, but it can happen to any of them.

    Someone in our shop just had to re-do a HG because he hadn't seen that there was a tiny gouge on the top of the block that stuck up a little bit and didn't let the head settle all the way down and seal the gasket on that corner. But that failure blew coolant out on the front of the engine block. A warped head will also not seal, so make sure it's flat.

    Another possibility on the black coolant could be that there is residue still in there from some improper coolant or additive that someone put in before you got the car and it's not all the way out yet. Not having heat is an indication that the coolant hasn't reached the heater core yet. That can take quite a bit of idling with the heat on max.

    I've also heard of rotted hoses making the coolant black.

    On the misfire, did you use genuine parts from Toyota? There are lots of reports of counterfeits causing people grief.

    But the misfire combined with the dark coolant makes me think it's the HG again.

    There are people here who do this a lot. Maybe one of them will come along soon to improve upon my suggestions.
     
    #3 jerrymildred, Mar 25, 2022
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