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Cadillac Seville / Cadillac Eldorado Forum Discussion, Are there two thermostats on '97 Eldorado? in Past Cadillac Vehicle Discussion; is the outlet of the purge line routed the same on a 96 seville and 97 eldo? i see my ...
  1. #31
    stoveguyy is offline Cadillac Owners Connoisseur
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    Re: Are there two thermostats on '97 Eldorado?

    is the outlet of the purge line routed the same on a 96 seville and 97 eldo? i see my purge line bolt outlet than loops back to a fitting under the throttlebody and the outlet of the TB line than goes to the pass side surge tank. i know the pic at thread #4 shows a 98 or newer seville? different purge line routing if i am correct.

  2. #32
    Submariner409's Avatar
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    Re: Are there two thermostats on '97 Eldorado?

    Some Northstars had a coolant heated throttlebody - the purge line ran from the hollow bolt/nipple to the TB tubes, then to the coolant reservoir. Those heated TB's were subject to the coolant tubes getting blocked with the (discontinued) tablet gunk. Later engines use the cast-in coolant passages in the water crossover to transfer heat to the TB bore.

    FWIW, due to the proximity of the TB to the water crossover on the earlier models, you can eliminate the TB coolant circuit and simply go straight from the hollow bolt/nipple to the reservoir. The less twists and turns the better.

  3. #33
    geegeeburr is offline Cadillac Owners Member
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    Re: Are there two thermostats on '97 Eldorado?

    Thanks for the steering pump picture, Ranger.

    Can I ask you guys a quick question about the block test? I'm going to do the block test one more time before returning the set to Auto Zone, and on the bulb that you squeeze, there is an open end, and an end with a little metal valve-jiggy in it. Which end goes into the container of blue liquid? Nowhere in the instructions does it say, and the guys at auto zone didn't know either. I did the test both ways the other day, but it would be nice to know for sure. There was no noticeable difference in the function or result.

  4. #34
    Submariner409's Avatar
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    Re: Are there two thermostats on '97 Eldorado?

    The bulb is a vacuum pump - the end that sucks pulls air from the space OVER the coolant in the surge tank. DO NOT pull any coolant - if you do you must wash the entire test set, discard the fluid, and start over.

    Hook it up so that bulb squeeze-release pulls bubbles through the test fluid.

  5. #35
    geegeeburr is offline Cadillac Owners Member
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    Re: Are there two thermostats on '97 Eldorado?

    Hi Sub. TY! I didn't pull in any coolant, just air. But, I got it now- the open end sucks in the air, and the valve-jiggy releases it through the top? (Figured it out by seeing which end sticks to my finger. I feel dumb now.)

  6. #36
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    Re: Are there two thermostats on '97 Eldorado?


  7. #37
    Aztec ETC ECS's Avatar
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    Re: Are there two thermostats on '97 Eldorado?

    Quote Originally Posted by Ranger View Post
    No. There is only one thermostat (like every other engine).
    Yesterday, I would have agreed with you. Not today, though.
    Hummer has 2:



    Go figure.

  8. #38
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    Re: Are there two thermostats on '97 Eldorado?

    Well I'll be dipped. Guess I should rephrase that to "most" every other engine.

    Wonder what the theory is behind that?

  9. #39
    Aztec ETC ECS's Avatar
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    Re: Are there two thermostats on '97 Eldorado?

    Quote Originally Posted by Ranger View Post
    Well I'll be dipped.
    Me too.

    Wonder what the theory is behind that?
    Same here.

  10. #40
    JimD is offline Cadillac Owners Connoisseur
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    Re: Are there two thermostats on '97 Eldorado?

    Quote Originally Posted by Ranger View Post
    Well I'll be dipped. Guess I should rephrase that to "most" every other engine.

    Wonder what the theory is behind that?
    Fail safe. What are the odds of two (parallel) thermostats failing to open?

    Remember, that is a civilian adaptation of a vehicle built to DOD specifications!

  11. #41
    MoistCabbage's Avatar
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    Quote Originally Posted by JimD
    Fail safe. What are the odds of two (parallel) thermostats failing to open?
    If I were behind enemy lines in desert conditions, I'd be more comfortable with the two.

  12. #42
    Zynder is offline Cadillac Owners Member
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    Re: Are there two thermostats on '97 Eldorado?

    While the Army is all about redundency, the fact that failsafe open thermo's exist (and I use them in all my cars) makes me doubt it is a backup thermo. My best guess is: dual levels of flow. To me in that picture, it appears the thermo on the left has a slightly smaller diameter center section and the nose of it sticks out a but further. Now most of you will say that is an aberration of perspective in the photo. It may be but I think I see what I see So just like my Seville's cooling fans are wired series for low speed, if that isn't cooling well enough, it swaps them both on to high speed. Same here. One thermo is set for a lower temp and if it can't do a good enough job cooling it, when it hits the 2nd thermo's temp it can open as well to double the amount of flow.

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    If it is for flow, and not intended as a fail safe, I doubt they open at different temperatures. More likely the reason would be to allow the high flow rate that the cooling system requires, while using standard size, off the shelf automotive thermostats.

    Speaking of "fail open" thermostats, they make absolutely no sense.

    If the engine is overheating, the thermostat will be wide open, and will stay open until the engine cools. All a fail safe thermostat does is lock open after a certain temperature is reached. If it's failed (seized), it isn't going to open that far in the first place. And if it isn't seized, and the engine overheats, not only do you have to repair the cause of the overheat, but you have to replace what would otherwise be a fully functional thermostat.

    How these made it into production, and why people buy them, is beyond me.

  14. #44
    Zynder is offline Cadillac Owners Member
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    Re: Are there two thermostats on '97 Eldorado?

    All of our industries as a whole are all about some commercial off the shelf parts. It ends up being cheaper most of the time, so your explanation is quite plausible.

    Why failsafe thermostats?

    Because if the wax inside the pellet has failed or the piston, the theromstat will snap back shut regardless of temperature. If it gets hot enough to push it out so the failsafe clips lock then no matter what happens it's open. Yeah that is not the biggest failure mode, I would think that would be a corroded closed one, but it happens enough it needed to be addressed. If you get it hot enough to boil the wax out or rupture the pellet it is in and it snaps back closed, not only do you have to figure out why it overheated, you'll probably be doing a head gasket change too. The failsafe thermostats cost about the same as a normal one, so this added protection may save your engine in this one particular failure mode for basically no cost. That's why they made it into production and that is why I buy them. I also drill 2 holes in the flanges so if they corrode shut, at least some water will get through. I got all the bases covered!

  15. #45
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    Re: Are there two thermostats on '97 Eldorado?

    Zynder, Your engine is currently a 4.9 - very, very, very different from a Northstar. It might be beneficial to study up on the Northstar cooling system to learn why a so-called "fail safe" thermostat is absolutely useless in this application. Also, in the 7.5 years I have been posting in CF I have seen only one - one - Northstar cooling system problem that MIGHT have been caused by the thermostat.

    It's also worthwhile to note that drilling extra holes in the Northstar thermostat plate is not recommended - let the thermostat control the temperature as it was designed to do. If you are a systems engineer, and feel that you have the cure for automotive engine cooling system problems, patent it and become a millionaire - and it's curious that no one else has pursued this course, even in the world's largest automobile manufacturing companies !

    QUICKLY !!!! Is the Northstar thermostat in the engine block outlet to the radiator or in the engine block inlet to the water pump ? (and what does the water pump cover do in the system design ???)

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