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Boiling sound at radiator cap

This is a discussion on Boiling sound at radiator cap within the General Help forums, part of the LSx Technical Help Section category; Came home from work today (20 minutes city driving), shut the car off, opened the hood to check something and ...

  1. #1
    Junior Member Blue2KTA's Avatar
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    Blue
    2000 Trans Am

    Boiling sound at radiator cap

    Came home from work today (20 minutes city driving), shut the car off, opened the hood to check something and after a few minutes I heard a boiling sound coming from the area around the radiator cap (no visible leaks). I could see the recovery tube move so I guess it was overflowing into the recovery tank. Normally the temp gauge (i know its not accurate,using it as reference) stays just under 210. While idling it went a hair over 210. I changed the water pump over a month ago and didn't have any temp issues after that. I used Prestone Dexcool 50/50 when I changed the pump. I checked the oil and its looks normal. Do I have a bad cap (original) ? Or is that 50/50 shit coolant ?
    I'm waiting for it to cool off and will check the level.

  2. #2
    Junior Member Blue2KTA's Avatar
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    Blue
    2000 Trans Am

    I went back outside and removed the cap. Radiator was full and recovery tank was at normal level. I let the car idle for 25 minutes with my scan tool connected. When temp hit 224 both fans turned on. At 215 the fans turned off. I shut the car off and waited, didn't hear the boiling sound anymore. IDK
    I took some coolant out of the radiator into a cup and compared it to some new coolant in a cup and you can tell the new is darker. Maybe too much water ?

  3. #3
    Electrical Engineer KMdef9's Avatar
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    Custom Swirly Black
    2001 WS6 M6

    Possibly. I can't see condensation accumulating that quick.

    You could just drain alittle and had some concentrated to it.
    Last edited by KMdef9; 04-19-2012 at 05:36 PM.

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    '02 WS.6 / '07 Suburban

    50/50 is a ripoff if you look at the price difference. Anyway, your cap may not have been fully seated and could have been bleeding off pressure. Keep an eye on it and if it seems to act up you could try replacing the cap. Wouldn't be the first time one has gone bad. Also, your dash temp gauge isn't all that accurate so don't put a whole lot of faith in what it is telling you. Double check things with a scanner or laser temp gun if you can.

  5. #5
    Junior Member Blue2KTA's Avatar
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    Blue
    2000 Trans Am

    I will try a new cap and pour some straight coolant. The temps are accurate, straight from my scan tool.

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    Go easy on the straight stuff. Taking it past the 50/50 concentration will actually decrease coolant performance - that is why you never run straight coolant in a vehicle.

  7. #7
    Junior Member Blue2KTA's Avatar
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    Blue
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    I checked the coolant with a one of those coolant testers with the 5 balls. Its showed 3 balls with the coolant from the car and 5 balls with new 50/50 coolant. I guess the coolant in the car is a bit watered down. Also picking up a new oem cap tomorrow.

  8. #8
    Junior Member Blue2KTA's Avatar
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    Blue
    2000 Trans Am

    Picked up the new cap today. Idled the car for about 25 minutes, turned it off and didn't hear anything boiling at the cap. The new cap looks slightly taller, maybe because the old spring is worn IDK

    2012-04-21 12.11.20 (Small).jpg

  9. #9
    Junior Member Blue2KTA's Avatar
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    Blue
    2000 Trans Am

    I drove back and forth to work today with the new cap. Temp was normal and no boiling when engine was turned off. I guess the cap was bad.
    $13 fix

  10. #10
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    Hopefully that was the issue. Good to hear.

  11. #11
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    midnight blue
    1998 Trans Am

    My car is doing the exact same thing, but it likes to blow the radiator reservoir cap off. It seems to have a lot of pressure... Was thinking head or head gasket but it still runs great, no radiator fluid in oil, changed cap no difference.. Thermostat is good pulled it out yesterday, the car also likes to get nice and warm as this is happening, only happening when I get in it. Drive like a Sally and she doesn't overheat.. I know this is a pressurized system, but I pulled both radiator hoses off and ran the car with straight water going into the water pump, did the same with the car off and it had the same flow rate, could this be the water pump? Please help!!

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