98 sls overheating
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Northstar Engines and System Technical Discussion Discussion, 98 sls overheating in Cadillac Engine Technical Discussion; 98 sls 130k miles.. recently my sls has begun to overheat after 10 minutes of driving or 20 minutes of ...
  1. #1
    tntitan is offline Cadillac Owners Member
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    98 sls overheating

    98 sls 130k miles.. recently my sls has begun to overheat after 10 minutes of driving or 20 minutes of idle. I have had a bad experience with the local stealership and have done recent work to the car myself or have had other local shops do it, which include myself changing the spark plugs, wires, fuel filter, oil filter, and thermostat, and a local shop replacing the front motor mount and front sway bars. This work has been done within the past couple of months. The car has always burned oil since I had it at 80k. I took it to Cadillac, and was told that it does burn exsessive oil, but I couldnt afford to fix it at the time, and was told as long as a put oil when it was low I would be okay.

    Overheating- 1st I have read the many threads about blown HG, and that will be the first thing my mechanic checks, but the purpose of the thread is for any addition help just in case. This is the first time the car my car began to ever overheat, and now it constantly does. Things that I have noticed is that my heat doesnt blow at hot as did before; I had a leak that the dealership diagnosed as a bad crossover gasket (used sealant tabs, and havent seen the leak since); and 1 time when the car overheated, it all of a sudden went back to reg temp.

    Any information, tips, tricks would be greatly appreciated, and relayed to my mechanic...

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    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 98 sls overheating

    Just test the coolant for the presence of exhaust gases.

  4. #3
    zonie77 is offline Cadillac Owners Connoisseur
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    Re: 98 sls overheating

    Yep, save time and money and do the coolant test first.

  5. #4
    jeffrsmith is offline Cadillac Owners Fanatic
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    Re: 98 sls overheating

    You can get the test kit at Napa for $50

  6. #5
    Destroyer's Avatar
    Destroyer is offline Cadillac Owners Master
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    Re: 98 sls overheating

    Save the $50. It's the head gaskets. It always is.

  7. #6
    32vmonte is offline Cadillac Owners Member
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    Re: 98 sls overheating

    Quote Originally Posted by Destroyer View Post
    Save the $50. It's the head gaskets. It always is.
    LOL, I'm reading on down the thread and see oh test the coolant for exhaust gases. You just plain out say it's done for.

    The test is still worth it to diagnose the issue.

  8. #7
    Ranger's Avatar
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    Re: 98 sls overheating

    Consider the source.

  9. #8
    Destroyer's Avatar
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    Re: 98 sls overheating

    Quote Originally Posted by Ranger View Post
    Consider the source.
    Are we betting?

  10. #9
    tateos's Avatar
    tateos is offline Cadillac Owners Connoisseur
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    Re: 98 sls overheating

    Quote Originally Posted by Destroyer View Post
    Save the $50. It's the head gaskets. It always is.
    Sorry guys, but I'm with Destroyer on this one - HG

  11. #10
    Ranger's Avatar
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    Re: 98 sls overheating

    I never said it wasn't. See post #2.

  12. #11
    tateos's Avatar
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    Re: 98 sls overheating

    Quote Originally Posted by Ranger View Post
    I never said it wasn't. See post #2.
    Yeah - I know Ranger I guess I was saying that Destroyer is right - no need for the test kit. Personally, I think that kit is a waste of $50.00. Use your auto skills, analysis, and judgment. If the coolant level starts off OK, the fans are coming on, the thermostat is opening, the purge line is clear, it's blowing coolant out the surge tank, I think almost certainly it's the HGs and block bolt holes - maybe a slight change of case porosity/cracked block/heads. I have had 2 different '97 N* engines exhibit these exact same symptoms, and tear-down showed it was head gaskets both times - no test kit required.

  13. #12
    Ranger's Avatar
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    Re: 98 sls overheating

    I agree. In this case I think it would be a waste of $50.

  14. #13
    Destroyer's Avatar
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    Re: 98 sls overheating

    You would not believe how many times I've seen this. There is a repair/bod shop next to my shop. N* Cadillac show up with over heating issues and the mechanic starts changing the water pump, t stat and even radiator and I tell him to stop because it's the head gaskets, he says it ain't cause there is no coolant mixing with the oil and no smoke out the tail pipe. I tried telling him that a N* does not do that. It was the head gaskets and he comes up to me saying "how the hell did you know that?". Not the first N* there BTW. I swear he does it just to make money on the water pump and other repairs and then break the bad news to the customer. He was not capable of the repair and turned the customer away. Anyway, he did the same thing to a '96 Taurus (they are also plagued with H/G issues but not as bad of a repair) the other day and the same thing happened.

  15. #14
    chp350 is offline Cadillac Owners Fanatic
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    Re: 98 sls overheating

    you say heater not getting as hot and one time it overheated and then went to reg temperature...my bet would be a bad thermostat...

  16. #15
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    Submariner409 is offline If it won't run, install a sound system
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    Re: 98 sls overheating

    In 4 years of head gasket and coolant loss discussions in here, only one thermostat has turned out to be bad.........and it's an easy test. Most Northstar thermostats begin at 188 and are fully open at 206. Drop the thermostat into a s/s pan of water and turn on the heat. If you feel like it, use a candy thermometer, and watch the disc. The water will be steaming pretty good as the disc starts to move, and, just before the water boils, the disc will be fully open.

    The 16 or 18 psi surge tank cap prevents boiling until about 256 degrees with a 50/50 coolant/water mix. The boil point goes up to a maximum of 267 degrees with a 70/30 (highest recommended concentration) mix.

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