Allante losing coolant via bypass

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Northstar Engines and System Technical Discussion Discussion, Allante losing coolant via bypass in Cadillac Engine Discussion; Have a 93 Allante which is blowing water past the radiator cap. This happens when the car goes uphill, or ...
  1. #1
    larry_pesch is offline Cadillac Owners Member
    Join Date
    Sep 2003
    Fresno, CA

    QuestionAllante losing coolant via bypass

    Have a 93 Allante which is blowing water past the radiator cap. This happens when the car goes uphill, or under heavy acceleration at operating temperature.

    Symtoms, when the car goes up a hill, coolant is blown out the overflow tube without any warning or increase in temp guage indicator. Once coolant start to surge out, coolant temperature rises and car overheats. Car never steams or makes any unusual heat induced noice. No funny smells. Once car loses coolant, runs hot until refilled and cycle starts over again.

    Driving in high temps (over 100 degrees) with air on, temp indicator swings slightly hotter, but car does not overheat. Fans seem to kick in and reduce temp.

    Before I go to the dealer and get bent over, any ideas? Car has:

    New clean, clear radiator, and coolant
    New water pump
    New radiator cap
    New fan relays
    New manifold temperature sensor

    Car runs perfectly, recently smogged in California with flying colors, no indication of coolant in oil, burning out the back, or loss of any kind other than the blow by.

    Make my day. Tell me where to go with this.


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  3. #2
    Allante North *'s Avatar
    Allante North * is offline Banned
    Automobile(s): 1993 Triple Black Allante
    Join Date
    Dec 2002
    Rocky Top Tennessee
    Hi Larry,


    I moved your thread to the Northstar section of the board to give it more attention and possible replies. I'm not sure of the suorce of your problem, but some of our other members might be. I am currious as to if you installed the cooling pellets on your radiator and coolant change. They are critical to the operation of the Northstar. You might search to find more information on the pellets if your not aware of them. I would elaborate, but I'm leaving for a trip and have limited time on the site tonite.

  4. #3
    eehoepp is offline Cadillac Owners Fanatic
    Automobile(s): 1994 STS - pearl white
    Join Date
    Feb 2003
    Bolton, Ontario, Canada

    Re: Allante losing coolant via bypass

    Quote Originally Posted by larry_pesch
    Make my day. Tell me where to go with this.

    Well, this may not make your day...

    Could be a blown headgasket. Combustion pressure leaking into the water jacket overpressures the cooling system. Coolant cap opens to relieve the pressure, thereby pumping out coolant.

    It's only noticeable under heavy acceleration or climbing hills because that's when the biggest air/fuel charge enters the cylinders & the highest pressures are generated.

    You can do a compression test to verify the head gaskets, or have a service shop do a sniffer test at the neck of the coolant reservoir. If the sniffer detects CO or HC in the coolant, the head gasket(s) need to be replaced.

    Good luck.

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