How Can I Purge Air out of Radiator ?

Discussion in '"How To" Request' started by bigstar101, Dec 23, 2012.

  1. bigstar101

    bigstar101 Junior Member

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    Hello All,

    I just signed up as I am having some issues with my wife's 2008 Cobalt LT.
    It has 86K Miles, everything runs fine its been overheating lately.

    It used to be stable at 189 F, but it started goin up to 200's, 210's up till 230 specially when going up hill, weird part if im going down hill it drops 20 degrees within minutes

    I Investigated and I had low coolant level, filled it up, it kept fluctuating from 189 to 200's this time. but it was running with no overheating issue any more. However a friend said it could be a bad thermostat with fauluty reading and suggested i replace.

    He swapped it out for me, and while replacing he drained the anti freez (dont know if he is supposed to do that, anyhow, he was able to put in the new thermostat, and filled the car with dex cool halfway and the rest with water as we didnt have much.

    now the car is worse, its overheating badly it even went up to 250F and kicked in cooling mode. He assumes there is air trapped.

    How can I purge the air out from the system ? is there a better solution? What wronge did he commit?

    I appreciate everybody's help and input!
     
  2. YelloEye

    YelloEye Super Moderator Staff Member

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    The purge point is near the upper radiator pipe, the hose going to the overflow tank.

    Get the car warmed up, turn it off, pop the overflow cap carefully so it doesn't overflow, close it back up, disconnect the small rubber hose above the upper rad hose.

    Ensure that the overflow tank has coolant in it at all times for this next part. Otherwise you'll just be pushing air into the whole system.

    Place a cloth over the nipple you removed the hose from, pressurize the overflow tank with an air compressor to push fluid down into the system.

    When the overflow cap makes noise you have put too much pressure into the system, try to keep from doing that.

    If fluid starts coming out of the nipple remove your air hose from the overflow line. Reconnect everything and take the car for a drive, ensure the heater works.

    Your rad fans should kick on around 208*F as recall.

    Hope I explained that clearly.
     
  3. bigstar101

    bigstar101 Junior Member

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    THanks for your reply,

    I am sort of a noob, is there a way you post an Image and show me the different locations.

    Thanks again for all your help, and Merry Christmas
     
  4. YelloEye

    YelloEye Super Moderator Staff Member

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    I know this isn't exactly your engine bay but the pieces we are looking at are the same.

    Pull off the black plastic engine cover by removing the oil cap and pulling on the cover. It has 3 or 4 soft connection points.

    Then you'll see this roughly
    [​IMG]

    That little silver pipe running in front of the valve cover is what we're after, disconnect it from the rubber hose on the drivers end by moving the clamp. Twist it back and forth to remove the pipe. Air goes towards the overflow tank. Bubbles will come out of the pipe end.
     
  5. bigstar101

    bigstar101 Junior Member

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    Excuse my ignorance

    But is the the silver pipe the one in Yellow or Blue

    thanks!!
     

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  6. YelloEye

    YelloEye Super Moderator Staff Member

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    Neither, it's the long thin pipe (~1/4") that runs horizontally above the intake manifold just in front of the valve cover. It's just to the left of your yellow circle.

    Center of this picture, running from the top left to lower right.
    [​IMG]
     
  7. bigstar101

    bigstar101 Junior Member

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    Yelloeye,

    First of all I appreciate all of your help :)

    Here is what happened,

    I had a mobile mech come out, (he came prior to ur post)

    we pull the plastic cover, undid the hose on the left hand side and poured antifreeze in there to push the out air, and it did push it out and fluid was back in the overflow tank. no leakaege at all.

    Turnd it on, idled for 8 minutes, stable at 160 F
    Took it for asping and within 5 min it went up to 220F (fans did kick in), we pulled over, and opened the hood and the engine was warm (normal), he even opened the overflow tank and it wasnt boiling.

    We are thinking the coolant temp sensor is defective?
    If I am correct what part should I buy? and do you possibly know where it is and how can it be swapped?!

    Thanks again for all your help!!
     
  8. YelloEye

    YelloEye Super Moderator Staff Member

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    Wait, so you poured fluid into the hose that runs to the overflow tank?
     
  9. bigstar101

    bigstar101 Junior Member

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    Yeah,

    check the picture, he opened up the plastic covers,

    and undid the hose under the yellow cirlce, and poured antifreeze there

    and I saw fluid increase in the overflow tank.

    did he jack it up ?
     

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  10. YelloEye

    YelloEye Super Moderator Staff Member

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    No not at all, but all that effectively did is add more coolant. The system needs to be pressurized to push the air bubbles out of the high point.

    So what he should have done is added compressed air into that same side of the line to push the bubbles out of the nipple side.

    Does that make more sense?

    I'll draw up a diagram when I get home today if you'd like. I wouldn't want you pushing more air into the system.
     
    Last edited: Dec 26, 2012

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