Over heating problems on a STS northstar.
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Cadillac Seville / Cadillac Eldorado Forum Discussion, Over heating problems on a STS northstar. in Past Cadillac Vehicle Discussion; I have been having over heating problems with my Seville lately and started throwing parts at it. So far I ...
  1. #1
    bikerbobby is offline Cadillac Owners Member
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    Over heating problems on a STS northstar.

    I have been having over heating problems with my Seville lately and started throwing parts at it. So far I have put a new water pump, new radiator, new coolant tank, new thermostat, checked the lower hose for the coiled wire. Everything checks out but it still over heats. I had a block test done to see if any chamber gases were going into the radiator but it passed a block test. I'm at the end of my rope. Any suggestions.

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    curtc's Avatar
    curtc is offline OCD - Obsessive Cadillac Disorder
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    Re: Over heating problems on a STS northstar.

    Sorry to hear about your Seville's troubles, you will probably get more responses/better forum assistance if you post this in the Seville section of the site...This is for the 05+ STS, totally different animal.

    BTW,
    Past Cadillac's

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  4. #3
    1BadCadSTS's Avatar
    1BadCadSTS is online now Cadillac Owners Connoisseur
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    Re: Over heating problems on a STS northstar.

    sounds like a blocked purge line or someone didnt do the exhaust gas test right and you have a blown head gasket (pulled head bolts)

  5. #4
    EChas3's Avatar
    EChas3 is offline Cadillac Owners Master
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    Re: Over heating problems on a STS northstar.

    It may evem pass a leakdown test but an emissions test of your coolent will likely prove the bad news.

    Oops, I misread the above post. Unfortunately, older N* HG's leak on acceleration.

  6. #5
    bikerbobby is offline Cadillac Owners Member
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    Over heating problems

    I have a 1997 Seville STS with the northstar engine. It started over heating so i started throwing parts at it. So far I put a new Radiator, water pump, thermostat and coolant tank with cap. I still over heats. So I had it block tested. It passed a block test so that means the head gaskets are ok right. Help

  7. #6
    98cadillac is offline Cadillac Owners Fanatic
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    Re: Over heating problems

    I assume you checked to make sure that the water pump belt/pulley/tensioner were in good condition when you replaced the water pump?

  8. #7
    RippyPartsDept's Avatar
    RippyPartsDept is offline Hi, I'm Chris - Please Read My Signature
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    Re: Over heating problems

    also check the purge line ... a clogged purge line will cause overheating

    also passing one block test does not mean your HGs are ok ...
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    amunderdog is offline Cadillac Owners Enthusiast
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    Re: Over heating problems

    Purge hose is flowing coolant?
    (Red Dot)

  10. #9
    bikerbobby is offline Cadillac Owners Member
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    Re: Over heating problems

    The belt and tensioner were both in good condition and it passed the block test three times during the coarse of the operation of parts swapping. Someone dumped a ton of stop leak in this vehicle before I got it. I will check that purge line. Thanks.

  11. #10
    Aztec ETC ECS's Avatar
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    Re: Over heating problems

    The point at the red dot in the pic is where they usually clog but you installed a new tank. Could still be clogged at the block. Pull the hose while running to check flow.
    Fans working?

  12. #11
    bikerbobby is offline Cadillac Owners Member
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    Re: Over heating problems

    Took the line off the expansion tank and blew air in both directions. Then put 2 more gallons of coolant. The fans are working but coming on a little late. Just after the gauge reads just passed the middle mark. will let you know how it goes.

  13. #12
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: Over heating problems

    The fans are working correctly - they don't even go to SLOW until 224 degrees (no A/C compressor function set in the HVAC system), which is a bit more than halfway between the middle (12 o'clock) mark and the next one. Your 12 o'clock mark covers from about 190 to 210 .......... yes, the "gauge" is highly damped at 12 o'clock.

    More about temperatures and the cooling system in the sticky posts at the top of the Engines, Northstar Performance threads page. (All stickys are full of necessary info .......... read them)

    There is an annotated gauge picture in my albums - if your gauge is a 135 degree sweep instead of the shown 180, the tick marks are still the same temperature readings. The Community tab, Albums, the two with the red Seville on the cover.

  14. #13
    Aztec ETC ECS's Avatar
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    Re: Over heating problems

    Quote Originally Posted by bikerbobby View Post
    Took the line off the expansion tank and blew air in both directions.
    Did you check the flow before you blew it out?

  15. #14
    bikerbobby is offline Cadillac Owners Member
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    Re: Over heating problems

    Thanks for all your help but I think the head gaskets are toast. Nothing seams to help and I have replaced and checked everything out. The fans are working on high and every component has been replaced. The purge line is clear, the lower hose has the spring in it so it can't collapse. There's nothing but the head gaskets left.

  16. #15
    Ranger's Avatar
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    Re: Over heating problems

    I tend to agree. The previous owner dumped the "repair-in-a-bottle" in the cooling system for a reason. Do the block test again, right after an overheat episode, but DO NOT add coolant before the test.

    Why oh why does everyone throw expensive parts and repair at an overheating problem in hopes that one will stick without doing a proper diagnosis?

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