99 Eldo overheating problem after new radiator.
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Cadillac Seville / Cadillac Eldorado Forum Discussion, 99 Eldo overheating problem after new radiator. in Past Cadillac Vehicle Discussion; Had radiator leak. Bought new radiator and installed it myself. No leaks. But now it is overheating worse than before. ...
  1. #1
    JDSKULL is offline Cadillac Owners Member
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    99 Eldo overheating problem after new radiator.

    Had radiator leak. Bought new radiator and installed it myself. No leaks. But now it is overheating worse than before. What did I do wrong?

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    Submariner409's Avatar
    Submariner409 is offline If it won't run, slap in a big stereo
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    Re: 99 Eldo overheating problem after new radiator.

    System bleed/purge procedures. If there are still air pockets in the system/heater circuit, the water pump cavitates and will not move coolant. The thermostat is in the radiator return line and is acted upon by block and heater circuit coolant temps. It's bassackwards from what you may be used to.

    Please rear the sticky posts on cooling systems, gauge operation, and fan operation in the Engines; Northstar forum.

    You might want to read the several threads on Northstar head gasket work, same list of stickys in the Northstar forum. Also, study the entire Cadillac Technical Archive way up ^^^ in the top black bar. That and stickys are timeless, necdessary info.

    Welcome to the Funny Farm.

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    basscatt's Avatar
    basscatt is online now Cadillac Owners Master
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    Re: 99 Eldo overheating problem after new radiator.

    Quote Originally Posted by JDSKULL View Post
    Had radiator leak. Bought new radiator and installed it myself. No leaks. But now it is overheating worse than before. What did I do wrong?
    ======================
    What did I do wrong?
    probably NOTHING -

    one of the most common causes of overheating after "OPENING" the cooling system -
    is air trapped in the system - due to a blocked PURGE LINE -

    -----------------

    the PURGE LINE is the only way of expelling air from the Northstar cooling system -

    it is a 3/8 diameter hose that goes from a hollow bolt in the thermostat/waterpump housing area of the engine - and plugs onto a nipple on the side of the SERGE TANK -

    with the engine running - there should be a gentle - constant flow of coolant - from the engine - to the serge tank -

    if there is no flow - the most likely cause is a blockage in the hollow bolt -

    follow the hose towards the engine - with the engine OFF - remove the hose - use a straightened metal coat hanger - or something similar - and poke it into the hollow bolt -

    the coat hanger should go in about 2 1/2 inches -

    once the hollow bolt is cleared - you can briefly start the engine to verify coolant flow - be sure to use some sort of container to catch the coolant so you don't make a mess -

    check the hose and serge tank for blockage -

    --------------------
    amunderdog likes this.

  5. #4
    JDSKULL is offline Cadillac Owners Member
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    Re: 99 Eldo overheating problem after new radiator.

    Purge line? Who'da thunk it. Thanks.

  6. #5
    basscatt's Avatar
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    Re: 99 Eldo overheating problem after new radiator.

    Quote Originally Posted by JDSKULL View Post
    Purge line? Who'da thunk it. Thanks.
    ---------------------------

    Cadillac also did some goofy stuff back then -

    they THOUGHT it was a good idea to use the hot coolant from the PURGE LINE -
    and run it through the throttle body to heat it up -
    and also run the coolant through the alternator - to cool ti down -

    I don't know if your car has these "features" -
    but if you do - you could bypass all that extra plumbing -
    and simply run a new hose from the hollow bolt -
    to the side of the serge tank -

    be sure to use reinforced GAS LINE -
    the PURGE LINE is part of the pressurized cooling system -

    oh - and be sure the alternator has a pulley with fins on it -
    to supply "air-cooling" -

  7. #6
    jake99seville's Avatar
    jake99seville is offline Cadillac Owners Member
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    Can anyone post a pic of the purge line in a 99 Eldorado/seville?

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    Submariner409's Avatar
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    Re: 99 Eldo overheating problem after new radiator.

    Pics in Tech Tips.

    The purge line runs from the hollow bolt/nipple on the water crossover, right next to the water pump cover/thermostat housing, and goes to a nipple on the side of the surge tank. In some pre-2000 models it also sent coolant to a passage around the throttlebody bore to heat it - possible icing during humid morning cold starts - so in your car it may run from the bolt/nipple, to the throttlebody fittings, and over to the side of the surge tank.

    If that throttlebody circuit is plugged the circuit cannot do its job of bleeding air and gas off the cooling system high point. Bypass the throttlebody circuit with a length of proper sized reinforced rubber fuel hose from any parts store - run straight from the hollow bolt/nipple to the side of the surge tank.
    Attached Images

  9. #8
    Submariner409's Avatar
    Submariner409 is offline If it won't run, slap in a big stereo
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    Re: 99 Eldo overheating problem after new radiator.

    Here's the 2000 and later engine without heated throttlebody. You get the idea .......................
    Attached Images

  10. #9
    Ranger's Avatar
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    Re: 99 Eldo overheating problem after new radiator.

    Quote Originally Posted by jake99seville View Post
    Can anyone post a pic of the purge line in a 99 Eldorado/seville?
    Here is a pic of both ends of it.
    Attached Images

  11. #10
    04GrandAmGT's Avatar
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    Re: 99 Eldo overheating problem after new radiator.

    There is the possibility of HG, if
    overheating worse than before
    check your purge line if thats clear, get a block test done.
    Replacing the Head Gaskets on a Northstar? Use our SureGrip Cylinder Head Stud Kit!


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