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Thread: Overheating - 1999 Deville

  1. #1
    hammarsve is offline Cadillac Owners Member
    Automobile(s): 99 deville
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    Overheating - 1999 Deville

    I have a 99 deville that overheated to 300+. No sign of leaking from pump, thermostat is good. Purge line is clear but is blowing hot air. I noticed a small amount of black oily sub coming from the hollow bolt. There is only air and no coolant circulating from the hollow bolt. Any help would b greatly appreciated.


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  3. #2
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: Overheating - 1999 Deville

    With the engine cold, does the cooling system hold pressure with a system tester ? If so, you're looking for a circulation problem. If not, the leak should be apparent.

    If the system has blown dry and there is in fact hot "air" blowing out the purge line bolt/nipple, then you're almost certainly in the head gasket replacement business. Refill the system, bleed the air, run the engine and perform a cylinder block exhaust gas test.

    Both test sets may be rented from a large parts store.

    Strange that your normal weekly underhood checks did not reveal low or empty coolant.

    http://www.sjdiscounttools.com/lis75500.html

  4. #3
    basscatt's Avatar
    basscatt is offline Cadillac Owners 10000+ Posts
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    Re: Overheating - 1999 Deville

    IF the serge tank is properly filled -
    and the PURGE line - specifically the hollow bolt - is clear -

    and all you get is hot air through the PURGE LINE -
    you probably have a head gasket problem -

    do a BLOCK TEST -
    the definitive test for failed head gaskets in a Northstar motor -

    and because you just joined - and this is your first post -
    I will add -
    DO NOT TRY ANY MECHANIC-IN-A-BOTTLE head gasket cures -

    NONE of them work -
    and WILL cause more problems if you decide to fix the engine -

  5. #4
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: Overheating - 1999 Deville

    I said most of that.

  6. #5
    hammarsve is offline Cadillac Owners Member
    Automobile(s): 99 deville
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    Re: Overheating - 1999 Deville

    Thanks for the info, will try a block test tomorrow. Yesterday it was running and the reservoir was bubbling over. The heat was blowing and it was holding a temp of 174. Shut car off for half hour, started again a very rough start, started overheating once again with no heat. Today won't even start, and no flow from hollow bolt, just a bit of black oily substance. After the major overheat I found one of the steel tubes was leaking coolant. I replaced that with some heater hose temporarily.

  7. #6
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: Overheating - 1999 Deville

    OK - You can completely bypass the coolant passage/tubes at the throttlebody. Run a single length of proper sized reinforced rubber fuel hose from the metal bolt/nipple to the side of the surge tank. The TB is coolant heated to prevent icing at the throttle blade perimeter during humid weather part-throttle operation. As it turns out, the heat was not needed - the 2000 and later do not have directly heated TBs.

    The bubbles thing is not good - not good at all. Head gasket breach indicator.

    The shutdown > rough start. Most likely coolant weeping into one or more cylinders.

    Go down to Engines, Northstar and study the 3 or 4 sticky posts on head gaskets, fans, cooling systems, and gauges.


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