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Thread: Heater core follows head gasket ?

  1. #1
    stoveguyy is offline Cadillac Owners Connoisseur
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    Heater core follows head gasket ?

    99 Seville. Bad heater core. Is there a link between high cooling system pressures due to bad headgaskets and failed heater cores or do heater cores on 99 Seville leak a lot? I see quite a few bad head/core cars for sale. Enough to make me wonder?


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    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: Heater core

    High cooling system pressures can blow up anything - and if the heater core was marginal to begin with it would not take much extra to pop it.

    Why do you suspect high system pressure ??

    What value is the existing pressure cap ??

    ........... or is this a hypothetical question about a dealer's or someone else's car ?

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    stoveguyy is offline Cadillac Owners Connoisseur
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    Re: Heater core

    hypothetical. i search alot for fixable cars and see the common issues. bad heads, new radiator, new water pump AND heater core? why do these cars seem to have so many common faults? age? cooling system neglect?

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    Re: Heater core

    My guess is the head gasket(s) blow and if anything else is weak in the system it's a daisy chain effect. Look at your thread title now - make more sense ?? If not I'll undo it.
    BUT................ many cars will go several hundred thousand miles with the original head gaskets and 3 heater cores and maybe a radiator or two - so where does that leave us ?

    There's an old adage in America's Cup racing sailboat crew circles - "If it never breaks it's too heavy !" I wonder if this might also apply to some automotive engineering ?

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    Re: Heater core follows head gasket ?

    I do not think there is a relationship. Cooling system pressure should vent at 15-18 psi (depending on the cap). The heater core should be designed and tested for well above that.

  7. #6
    stoveguyy is offline Cadillac Owners Connoisseur
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    So the odds of the 99 SLS I am looking at with bad heater core has a good motor? Since most agree 99 yr cars have the worst HG failure rate.

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    Re: Heater core follows head gasket ?

    Odds of having a good motor ?? Somewhere between 100% and 0%. Seriously - the "good" determination is up to you, and every shred of knowledge you'll need is already posted in this forum and just above in Cadillac Tech Tips and the Northstar cooling system and head bolt stickys.

    Nobody - sight unseen - can say that a bad heater core does or does not have anything to do with possibly failed head gasket(s).

  9. #8
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    Re: Heater core follows head gasket ?

    Quote Originally Posted by stoveguyy View Post
    So the odds of the 99 SLS I am looking at with bad heater core has a good motor? Since most agree 99 yr cars have the worst HG failure rate.
    I wouldn't give you odds either way.

  10. #9
    billbrownfarm is offline Cadillac Owners Member
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    Re: Heater core follows head gasket ?

    Lets put it this way. Out of the three Norstars I have, two have blown head gaskets and stripped head bolts at under 150k miles. The other I bought at an auction with 160k and may have already been rebuilt. I'd figure if it has over 125k it is getting ready to blow the head gaskets.

  11. #10
    billbrownfarm is offline Cadillac Owners Member
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    Re: Heater core follows head gasket ?

    Here is another one for you. I replaced the radiators in both of the Norstar/Cads a couple of months before I took them apart for stripped head bold/ head gasket issues. I remember there was a bulge on the other side of the top radiator hose inlet with a crack through the center on each of them. To me it looked like the hard plastic radiator housing had started to melt in that area. Maybe when I stomp on a Norstar with stripped head bolts exhaust mixes with the antifreeze and it is to much heat for the radiator or heater core (if the heater is on) to handle?

  12. #11
    Submariner409's Avatar
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    Re: Heater core follows head gasket ?

    I doubt that - pressure and water pump cavitation (due to loss of coolant) is the overheat culprit, not gas-in-the-coolant temperature.

    If the engne "overheats" at 260 degrees that's still way below the temps at which thermoplastic begins to deform.


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