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  1. #1

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    Thermostat stuck open? No Heat!

    Update: I HAVE HEAT AGAIN! Turned out to be air in the system. Turns out the guy who did it last time filled the reservoir first before filling the rad from the filler neck, and then topped it off from the filler neck, which probably trapped air into the system. I went ahead and drained the coolant and re-filled it properly, ensuring I bled it well via the thermo bleed valve and the one above the water pump. Thanks for the info guys! This place is awesome.

    Yesterday my heat decided to crap out on me (the ONE day that mother nature decides to throw a freak spring snowstorm into my area), I've opened up the passengerside dash to check the actuators, and both seem to work fine, as does the door that opens up when I turn on the AC.

    Just to be clear, as I am not 100% sure if they are the actuators I've been reading about that control the heat door, but these two things work fine:


    If those AREN'T the actuators/temp door motors, then where is it, exactly?

    I noticed it started happening when I was driving last night, the temp gauge was rising at quite a noticeable rate, past the halfway mark (105 Celsius or 221 F) and rising, so I decided to turn on the heat, and thats when I saw the temperature drop rapidly back down to the typical range (~65C or 150F) for my car but the heat would not work.

    I also checked under the hood, and when I pinch the tube coming out of the thermostat back to the rad, I can hear the coolant slosh in the tube from the other side of the engine near the belts (the input tube?) even when the car is off. Wouldn't the thermostat be closed when the car is off, and so coolant wouldn't be moving between the two hoses? That is my main clue that I am thinking the thermo might be stuck open.

    Thanks!
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  2. #2
    ManicMechanic's Avatar
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    Re: Thermostat stuck open? No Heat!

    The thermostat will still be open until the engine cools past the opening temp.

    But you very likely have a stuck thermostat and likely low coolant.
    Jay
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  3. #3
    1990lumina's Avatar
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    Re: Thermostat stuck open? No Heat!

    Depending on which engine this happened, I'd just change the t-stat regardless. On my 3.1 it's a 5 minute job, and that includes topping off the coolant again.
    Jeff L. :: 2nd Canadian to win COTM The Preservation for POS W-bodies Canada Chapter
    2004 Acura TSX | 2.4L I4 iVTEC; 5 Speed Auto | 1 of Many Made In '04 | 89,XXXKM
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  4. #4

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    Re: Thermostat stuck open? No Heat!

    its sounds like you have low coolant and air trapped along the heater supply line = no heat.

    I've experienced this when changing the coolant and air gets trapped in heater core = no heat. Open the heater valve to hottest setting and top off coolant and make sure air is bled out.

    Shouldn't hear sloshing noises, that means there's air in the lines. Changing out T-stat would be good insurance since you're going to be in warm weather soon.
    Former owner: &#39;92 Z34 - 5 speed

  5. #5

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    Re: Thermostat stuck open? No Heat!

    Yah I recently changed the coolant, so there might still be air in the line, but when I open the radiator cap, the tube is already full of coolant, and when I open the bleeder valve on the thermo housing hot coolant comes out and no air. Any way else I can make sure all the air is out of the system?

    Quote Originally Posted by 1990lumina
    Depending on which engine this happened, I'd just change the t-stat regardless. On my 3.1 it's a 5 minute job, and that includes topping off the coolant again.
    It is the 3.1, and it does look simple, but do i have to drain a bit of the coolant out first before taking out the thermostat?

    My coolant levels seem fine as the backup reservoir is full, and the temp gauge reads normal (one notch below half-way which is 105C/221F)
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  6. #6

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    Re: Thermostat stuck open? No Heat!

    Okay, I'm pretty sure I have air in my system, but I can't get it out and I'm really confused. Here are my observations:

    • Coolant reservoir stays at the 'hot' level even when cold (not 100% sure on this, will have to check in the morning, but pretty sure it doesn't go down even when cold)
    • When warmed up, both bleed valves spurt coolant
    • Upper rad hose collapses (i.e. is squishy) even if coolant is flowing through (thermo bleed valve squirts)
    • When warmed up, radiator is full (coolant comes out when rad cap unscrewed while engine on)
    • No pressure/coolant does not squirt just several minutes after engine shut off
    • When engine is off, gently pinching and unpinching upper coolant hose causes coolant in fill tube to slowly go down


    I guess I'll either drain all the coolant and refill and re-bleed it, or take it to some place and have them empty and re-fill the coolant as I clearly don't know how to do it properly.
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