96 Deville coolant problem
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1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, 96 Deville coolant problem in Past Cadillac Vehicle Discussion; Howdy! First post... 96 Sedan Deville with that overengineered/underengineered Northstar... Have an unusual problem. Top off coolant, and I can ...
  1. #1
    Legendary Thunder is offline Cadillac Owners Member
    Automobile(s): 1996 Sedan Deville
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    96 Deville coolant problem

    Howdy! First post...

    96 Sedan Deville with that overengineered/underengineered Northstar...

    Have an unusual problem. Top off coolant, and I can run anywhere from around town speeds, to 80+ on the highway, temp stays right in range ( 196 around town, 192 on highway) I can run this way for hours... Till I shut it off and restart within 10 minutes...

    After I shut it off, temp starts climbing to around 220, and when I restart it it begins blowing coolant from the reserve immediatly, and temp starts to climb rapidly. If I drop it into second gear when at 45 mph, temp drops to normal, and it stops blowing coolant.

    Any ideas? Im stumped...

    Rich T


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  3. #2
    bigm57ict's Avatar
    bigm57ict is offline Cadillac Owners Connoisseur
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    Re: 96 Deville coolant problem

    Temp rising to 220 after shutdown sounds totally normal. I don't think the fans even kick on at that temp.

    I'm not sure about the blowing coolant. Hopefully someone else more versed in Northstar will chime in.
    I am curious, though - How can you tell what's happening at 45 mph and in second gear? Do you have a transparent hood?

  4. #3
    Legendary Thunder is offline Cadillac Owners Member
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    Thread Starter

    Re: 96 Deville coolant problem

    I keep my spare midget under the hood with a 2-way radio... lol.

    I can hear it and feel it when its spewing, and the temp readout tells me the temp drops.

    My relays fried years ago, and I replaced it with a hi pro thermostat for the fans with an idiot light mounted under the hood so when I know my fans are cycling. Fans kick on at 200.

    I really am stumped...

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  6. #4
    basscatt's Avatar
    basscatt is offline Cadillac Owners 10000+ Posts
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    Re: 96 Deville coolant problem

    FULL in the expansion tank is actually about half full -

    if you fill it to the top -
    there is no space for the coolant to expand -
    and will "boil-out" -

    check your pressure cap -
    be sure it holds 15PSI -

    check the water pump belt/tensioner/and idler pulley bearing -
    be sure the belt is tight -

    check the 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 -

  7. #5
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 96 Deville coolant problem

    Quote Originally Posted by Legendary Thunder View Post
    After I shut it off, temp starts climbing to around 220, and when I restart it it begins blowing coolant from the reserve immediatly, and temp starts to climb rapidly. If I drop it into second gear when at 45 mph, temp drops to normal, and it stops blowing coolant.
    Sounds suspiciously like a bad cap. It's cheap enough that it would be worth replacing it.

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