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High Coolant Temperature

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Luke Burrow, Aug 15, 2016.

  1. Luke Burrow

    Luke Burrow New Member

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    2005 Prius
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    Greetings, Priuschat folks!

    I drive a 2005 Prius with 190,000 miles. A few weeks ago, after driving a few hundred miles on a road trip, my wife and I received the red triangle warning light, along with a high coolant temperature warning. We pulled it over to the nearest mechanic, who took a quick look at it just to see if they could find any leaks. They couldn't see any problems, added some water to the radiator, and sent us on our way. We actually managed to make it to our destination, and then another 350 miles home, simply by continuing to add water to the radiator every time we received the warning light (it took about a quarter gallon every time before filling to the top).

    By the time we got home, we also had a CEL for code P1150. We took it to the service department of the nearest dealership, and they flushed the coolant system, added new coolant (replacing the 3/4 gallons of water we added on our drive home), and presumably bled the air out of the system. After receiving the car back, everything was fine for about a week, and then we started receiving the same high coolant temperature warning. Once or twice during that week (though not constantly), I heard sloshing from behind the dashboard when starting the car up.

    Took it back to Toyota, and they couldn't find anything wrong. They said the problem may be with a particular sticky valve (they didn't actually tell me which, and unfortunately, but I think they're referring to the coolant control valve), but they couldn't actually get it to stick. They quoted me 500 dollars to replace that particular part, but said to hold off, because they couldn't be sure that was the problem. They also told me that if that was indeed the problem, I probably wouldn't ruin the engine if I just drove on the problem without fixing it, though I'm not entirely confident in that assessment.

    I got myself a bluetooth OBD reader that connects to my phone (I can't afford a Scangauge), just so that I could see for myself the actual coolant temperature. My wife drives the car to work about 15 miles in the morning without trouble (peaking at about 70 mph on the interstate), but on the drive home (after sitting in 95+ degree humid weather all day), it gives her the warning at about the same place on the interstate every time. Sure enough, according to the reader, the coolant temperature peaks at around 245 degrees while she's on the interstate.

    You folks know a lot more about these things than I do, so I wanted to throw it out there and get some opinions. I don't know the first thing about car maintenance, so I don't see myself doing any of the repairs myself without causing more problems than I solve. Should I shell out the money to replace this valve? Do you think the problem might be elsewhere? I'm interested to hear your opinions!

    Edit: Oh, and one final thing worth noting—after only a few minutes, we can still get very good temperatures from the heat in the cabin, which doesn't seem to be the case for many people who have similar issues. Not sure exactly what to make of that.
     
    #1 Luke Burrow, Aug 15, 2016
    Last edited: Aug 15, 2016
  2. jadziasman

    jadziasman Prius owner emeritus

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    Okay Luke, if you're adding coolant/water there must be a leak somewhere and a fairly sizable one at that if you're adding 3/4 of a gallon during a road trip. You appear to be having a problem similar to what BillS experienced. Here's the link to his thread:

    Prius, overheating P1150. Coolant loss. Replaced Everything | PriusChat

    Hopefully you won't need a new head gasket like he did. If you're lucky, it might just be a clogged radiator - however coolant loss isn't usually a problem with that - just overheating. I hope you find a competent mechanic. BillS went to a Toyota stealership and they told him it WASN'T the head gasket when it actually was.
     
    #2 jadziasman, Aug 15, 2016
  3. Patrick Wong

    Patrick Wong DIY Enthusiast

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    1. When accelerating hard, if you see white smoke, the problem is that engine coolant is leaking through the cylinder head gasket and is being burnt in the combustion chambers.
    2. If you do not see this, yet the engine coolant level drops so much, then it is guaranteed that a leak exists. The most likely place for an engine coolant leak is at the engine coolant pump bearing. Look at the inside of the pump pulley for signs of dried antifreeze which will be pinkish or whitish if the correct Toyota coolant is being used. The next most likely place for a leak is at the engine radiator due to debris impact or other damage.
    3. The correct engine temperature is near 82 degrees C or 180 degrees F, which is the temp where the engine thermostat opens. 212 degrees F is boiling temp for pure water. Each time you allow the engine head to reach 245 degrees F (due to lack of coolant at the temp sensor), you are causing engine damage.
    4. The engine coolant valve is not causing the leak or the overheating issue. The leak is the main problem that needs to be immediately fixed or permanent engine damage will result (if it has not already happened).
    5. If the cabin heater produces good heat, at least the coolant loop through the cabin heater core does not have air in it.
    6. While looking at the engine coolant pump bearing, inspect the serpentine drive belt which spins the pump pulley. A few owners have actually lost that belt (due to excessive wear of the belt or the pump bearing failing) and had no idea it was gone - then wondered why the engine was overheating.
     
    #3 Patrick Wong, Aug 15, 2016
    Last edited: Aug 15, 2016
  4. Kevin_Denver

    Kevin_Denver Active Member

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    2009 Prius
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    There are basically two possible causes I can think of
    1. There's a leak somewhere in the engine coolant system causing the radiator fluid to leak out.
    2. There's a leak in one of the engine gaskets causing exhaust gas to get pushed into the engine coolant system, and it's pressurizing it and causing the coolant to leak out of the overflow.

    As the system has been inspected by two mechanics, it's probably not number 1. A check to see if it's number 2 is to get a water bottle and strap it to the car with the overflow tube where you add radiator fluid fed into the water bottle. Then drive the car in a situation that stresses the engine and engine heat. If when you finish you find fluid in the water bottle, then you know that the source of your leak is from the overflow tube and it's most likely number 2.

    Until you have the problem solved, I would monitor the temperature closely, and do whatever is needed to keep the car's temperature below 212F or 100C. Running above this point for any kind of extended period will damage the engine.
     
    #4 Kevin_Denver, Aug 19, 2016
    Last edited: Aug 19, 2016
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