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Cadillac Seville / Cadillac Eldorado Forum Discussion, 1997 SLS still overheating in Past Cadillac Vehicle Discussion; You want to see the flow characteristics, and uncorked is the way to go. The flow, if correct, is the ...
  1. #16
    Submariner409's Avatar
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    Re: 1997 SLS still overheating

    You want to see the flow characteristics, and uncorked is the way to go. The flow, if correct, is the same whether the system is under pressure (cap on) or not - the surge tank is part of the pressurized system: it is not an overflow bottle as used in the obsolete coolant recovery systems. The purge line is merely a system high point bleed to the (pressurized) airspace over the coolant.

  2. #17
    ramblerusa is offline Cadillac Owners Member
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    Re: 1997 SLS still overheating

    The engine has been off for 4 hours, is that sufficiently cool enough to remove radiator cap? Sorry for so many questions.

  3. #18
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    Re: 1997 SLS still overheating

    Go for it ........... The main reason for advice to do the coolant flow/level tests with the engine cold is the very distinct possibility of severe burns - 200+ degree coolant can really cook your face.

    But .......... level checks are done cold because of the large coolant expansion with temperature increase - all normal, all taken into account when the systems are designed.

  4. #19
    ramblerusa is offline Cadillac Owners Member
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    Re: 1997 SLS still overheating

    Just did purge test. Coolant flows steadily into makeshift container. I guess this means head gasket failure............

    ----------

    I can drive around for 30 minutes without AC on, but temp gauge goes up after 15 or 20 minutes with AC on. What are the odds that the temperature gauge is bad, and the engine isn't truly overheating?
    I've already had the radiator temp sensor replaced so I know that's not the problem.

  5. #20
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    Re: 1997 SLS still overheating

    If you have coolant flow from the purge line and still are overheating, that is not a good sign, but it alone is not enough to condemn the HG's. You need to get a block test kit and run that test after an overheat episode (or have it done by a radiator shop or mechanic). You can borrow the kit from AutoZone and just pay for the test fluid.

    A bad temp sensor is possible, but not common (or probable).

  6. #21
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    eldorado_sean is offline Cadillac Owners Fanatic
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    Do the block test first. If it isn't the HG then go for the temp sensor.

  7. #22
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    Re: 1997 SLS still overheating

    No such thing as a radiator temp sensor.

  8. #23
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    Re: 1997 SLS still overheating

    I completely missed that one.

  9. #24
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    eldorado_sean is offline Cadillac Owners Fanatic
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    Does he mean coolant temp sensor?

  10. #25
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    Only one coolant related temp sensor in the car.

  11. #26
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    Re: 1997 SLS still overheating

    If the purge line flows steady with no bubbles in it then the HG is highly unlikely.
    Let's not forget what the HG issue is causing: combustion gas passing from the cylinders to the coolant jackets, thus adding gas to the sealed coolant system. All this gas will eventually end up in the surge tank (through the purge line). Thus if you disconnect the purge line you can see the bubbles coming to the surge tank.
    Obviously at some point the pressure will be higher than 15PSI so the cap will open, some of the coolant along with the gas will be blown out through the overflow line. In some cases other weak points of the cooling system will give first (like the rad. plastic side tanks, the surge tank). This is how you lose coolant, the other coolant you lose seeps in the cylinders (mainly when the engine is off) and that's why you get rough idle and difficult cold startups (along with the steam out of the tailpipes).
    You don't seem to have any of these.
    You mentioned something about a changed rad. and something with the WP. Is the WP belt OK, nice and tight?

  12. #27
    mike5514 is offline Cadillac Owners Enthusiast
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    Re: 1997 SLS still overheating

    All good advice! If I may add inspect the water pump belt and do a system pressure check.Mike

  13. #28
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    Re: 1997 SLS still overheating

    Quote Originally Posted by eldorado_sean View Post
    Does he mean coolant temp sensor?
    Most likely.

  14. #29
    ramblerusa is offline Cadillac Owners Member
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    Re: 1997 SLS still overheating

    The coolant temp sensor has already been replaced.....The car overheated yesterday on the way home from work after only 5 minutes with AC on.
    After $2k in cooling system repairs, the end is apparently near for this car. No AC in 100 degree weather is not an option here.....

  15. #30
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    Re: 1997 SLS still overheating

    Has anyone mentioned the heater hoses?

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