Over-Heating... T-Stat?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by HeavyFooted3SGTE, Oct 21, 2018.

  1. HeavyFooted3SGTE

    HeavyFooted3SGTE Junior Member

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    2011 Prius. 215k Miles. No codes/CEL. The Engine Coolant Temp light comes on sporadically. Coolant level is full and it looks like the stock pink. I hooked up a OBD scanner and ran live time diagnostics. At idle(in regular or maintenance mode) and low-speeds, the car runs between 195-215 degrees and is fine. Above 30 mph in city and highway driving, the temps are between 200-220 deg but then jump to 250-260 deg quickly and trips the coolant temp light to come on. It doesn't last a long time and it comes back down quick. But this repeats itself with no pattern. The car developed a stutter during cold start-ups about three months ago. I changed the spark plugs and cleaned the EGR pipe. I did not clean the EGR cooler. Coolant was flushed 3 years ago, but again the level is good and the color is good. I did some searching but did not come to any conclusions.

    I'm thinking Thermostat. Any thoughts? Thanks
     
    #1 HeavyFooted3SGTE, Oct 21, 2018
    Last edited: Oct 21, 2018
  2. fuzzy1

    fuzzy1 Senior Member

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    Both my past 2010 and current 2012 normally run at 195F. The electric fan kicks in at 202-204F, and I've never seen it go above 204. Is your cooling fan operating?
     
    #2 fuzzy1, Oct 21, 2018
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  3. HeavyFooted3SGTE

    HeavyFooted3SGTE Junior Member

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    Yes it is.
     
    #3 HeavyFooted3SGTE, Oct 21, 2018
  4. Dxta

    Dxta Senior Member

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    Any codes on the car?
     
    #4 Dxta, Oct 21, 2018
  5. Dxta

    Dxta Senior Member

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    Have you checked the operations of the inverter pump?
     
    #5 Dxta, Oct 21, 2018
  6. ChapmanF

    ChapmanF Senior Member

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    Car thermostats are very mechanically simple and nearly bulletproof. They open because of a wax pellet that expands when it gets hot. They close because of a spring.

    A very corroded thermostat might fail to close completely (leading to a car that "underheats"). On the other hand, the force of the expanding wax is such that pretty much nothing stops a thermostat from opening. The only way you get a "stuck closed" stat is if the engine already severely overheated once for some other reason, and got so hot that the expanding wax burst the thermostat. A thermostat after that happens is permanently crippled.

    You don't really see a thermostat that opens, keeps the car at normal temps for a while, then closes and lets the car overheat, then changes its mind and opens again. Expanding wax just doesn't really do that.

    I would wonder if maybe your 2011's electric water pump could be intermittently failing, though I'd be surprised to have no codes with that. Can you put it through its paces with the Techstream active tests?

    If you do take out the thermostat, they're easy to test. You need a pan of water, a stove, and a thermometer. Would be interesting to see what you find.

    -Chap
     
    #6 ChapmanF, Oct 21, 2018
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  7. HeavyFooted3SGTE

    HeavyFooted3SGTE Junior Member

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    Thanks for the reply. I can take out both the t-stat and pump at the same time since they are right there. I'm only familiar with mechanical water pumps and how they fail.
     
    #7 HeavyFooted3SGTE, Oct 21, 2018
  8. ChapmanF

    ChapmanF Senior Member

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    If you've got Techstream, you can just put the car ON (not READY) and tell it to spin the pump, and what speed. Maybe give it a listen with a mechanic's stethoscope, or at least make sure the coolant is flowing.

    -Chap
     
    #8 ChapmanF, Oct 21, 2018
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  9. HeavyFooted3SGTE

    HeavyFooted3SGTE Junior Member

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    I don't have a techstream or a stethoscope, just a OBD2 reader that gives 39 different stats of the car. Is there another way to check?
     
    #9 HeavyFooted3SGTE, Oct 21, 2018
  10. ChapmanF

    ChapmanF Senior Member

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    Might check for a busted impeller as shown toward the end of this thread....

    -Chap
     
    #10 ChapmanF, Oct 21, 2018
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