radiator hoses on 2007 prius both hot or not?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Prius2007A, Mar 26, 2020.

  1. Prius2007A

    Prius2007A New Member

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    I just finished installing a water control valve and then I bled all three cooling systems. Now, I'm not clear as to whether or not the radiator hose closest to the radiator fill tube (also connected to the thermostat housing) is suppose to get hot or not? The other hose closest to the bleed valve is consistently hot after the engine has warmed up. The heater works fine and other than the error code for the water control valve assembly no other codes or warning lights have come on.
     
  2. SFO

    SFO Senior Member

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    Welcome to PriusChat!!

    You've replace the water control valve, and still have a related error code after scanning?

    Which OBD2 scanning device are you using to retrieve the DTCs, and which DTC did you retrieve after replacement?

    Is it possible that the hoses were crossed during reassembly?

    Your profile lists 'california', which is a fairly large area.
     
  3. valde3

    valde3 Senior Member

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    Radiator hose that connects to thermostat housing (lower radiator hose) is the return hose from radiator. Its temperature depends on how hot the radiator is. If radiator is cool that hose is cool.

    To get that hose hot put the Prius in maintenance mode to get the engine to run constantly and turn the ac completely off (by turning the fan off) (that will make sure the radiator fan is not commanded on by ac). Then wait until radiator fan starts by that time radiator is hot and the hose is hot also.

    Try to make sure not to overheat the engine doing this. Best is if you have some way of checking the engine temperature and periodically check that the heater is working (by turning it on for short time). Radiator fan will turn on when engine gets to 96c (205F). This is normally the method that's used (besides other things) when filling the coolant on most of cars.
     
  4. sam spade 2

    sam spade 2 Senior Member

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    Simple answer: If the engine if fully warmed up, then yes both hoses should be hot to the touch.
     
  5. valde3

    valde3 Senior Member

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    Not really or only in hot weather. In cold weather it will newer get hot as thermostat is mostly closed. And if it's warm and ac is in use it still might not get hot as ac will keep the radiator fans running and cools the radiator enough to keep the thermostat partially closed.
     
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  6. sam spade 2

    sam spade 2 Senior Member

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    IF THE ENGINE IS FULLY WARMED UP.......was the qualifier in my post.
    The "exceptions" that you are offering don't fit that situation.
    Some of these cars do not HAVE a conventional thermostat.
     
  7. valde3

    valde3 Senior Member

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    Here's some basic info on how thermostat and cooling system works: Thermostat: how it works, symptoms, problems, testing that's just one link I happened to find. Look at the first picture it shows how lower radiator hose is cooler than upper (engine as about the same temperature as coolant in upper hose).

    The chart in the website is when idling. But even in it we can see that engine can be at 85c (185F) (clearly fully warmed up) with lower hose only slightly warm. When driving (or if fan is running for some reason) radiator and lower radiator hose newer get as hot as in that chart. Colder the outside temperature colder they will be. Engine can be fully warmed up in cold weather and (in cold enough weather) lower radiator hose could even be at about 0c or 32F.

    Gen 2 Prius does have a conventional thermostat. Of course if somebody would remove it for some (weird) reason then it would work as you describe it. With thermostat removed lower radiator hose would be hot when engine would (finally) be fully warmed up. Same thing would be true if thermostat failed in open position.
     
    #7 valde3, Mar 26, 2020
    Last edited: Mar 26, 2020
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  8. sam spade 2

    sam spade 2 Senior Member

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    I guess this is one of those cases where you MUST have the last word, be it right or wrong.

    I KNOW how a conventional thermostat works.
    I also know that under most conditions, there is enough thermal mass in the engine block and the coolant so that once things get "hot" the thermostat will open and STAY open as long as the engine runs occasionally.
    And I never said that the lower hose would not be somewhat cooler.
    I said it would still feel hot to the touch.

    The initial question was: Should both hoses feel hot ?
    And the correct answer is: Yes.
    Done.
     
  9. valde3

    valde3 Senior Member

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    Sorry but it's you who is the one who has to have the last word even though you're wrong.

    No way is there enough thermal mass in the engine to keep the thermostat constantly open when engine only runs occasionally!

    Thermostat in a (Gen 2) Prius starts to open at 82c (180F) and is fully opened at 92c (198F). Let's think the engine is running at 85c thermostat is less than half open at that point. Then the engine stops with even a bit of heater use or AC turned on (radiator fan running) it will take maybe couple of minutes for engine to cool down to 80c (176F) where thermostat is fully closed. Engine can stay off for longer than that even with AC use if the AC is not working that hard. With heater use engine can be off for lot longer than that.

    Temperature of the return hose will be effected by lots of things including the outside temperature. Even in relatively hot weather it can only be something like 50c (122F). Ok you might say that's hot but somebody might not.

    But in really cold weather it could be about 0c (32F) and nobody would say that's hot.

    So to question: Should both hoses feel hot?
    Correct answer still is: It depends on a lot's of things. In some conditions it's normal for it to be only a bit warm or even cold.
     
  10. sam spade 2

    sam spade 2 Senior Member

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    How do you manage to run your conventional hybrid car so that the engine runs only occasionally ??
    I quit.
    You should too.
     
  11. valde3

    valde3 Senior Member

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    Ok maybe not the perfect choice of word there. But engine doesn't run constantly either.

    If you had some way of monitoring the engine temperature you would see how it drops when engine is not running. Especially if you use heater at all.
     
    #11 valde3, Mar 27, 2020
    Last edited: Mar 28, 2020
  12. valde3

    valde3 Senior Member

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    I actually tested this today. Temperature was relatively warm at 5c (41F) and engine had fully warmed up. Heater was set at the lowest setting 16c (61F). I was driving at about 55km/h (34MPH). Engine temperature was 88c (190F) when it shut down and car kept going on hybrid battery. Engine temperature had drop to 78c (172F) when engine was started to charge up the hybrid battery and to keep the car going.

    Toyota manual would tel you to replace the thermostat if it's not fully closed at 78c (172F). So there's clearly not enough heat mass in the engine to keep the thermostat open while the engine is not running!
     
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