Disappearing Coolant
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Cadillac Seville / Cadillac Eldorado Forum Discussion, Disappearing Coolant in Past Cadillac Vehicle Discussion; I have a 1987 Eldorado with 76,000 miles on it. I've had to add a gallon or so of water ...
  1. #1
    mmayer110 is offline Cadillac Owners Member
    Automobile(s): Eldorado 1987
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    Disappearing Coolant

    I have a 1987 Eldorado with 76,000 miles on it. I've had to add a gallon or so of water to my coolant reservoir every 60 miles or so lately. I would attribute it to the head gasket but no steam comes out the tail pipe. No water is mixed with the oil...oil is very clear and clean. The engine runs very smoothly, and when properly filled, the engine runs very cool. There is never a puddle of coolant under the car...or any other fluid for that matter. My mechanic said he tested the compression and everything was fine. We're all out of ideas. Does anyone have a new idea?

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    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Disappearing Coolant



    Small coolant leaks can evaporate before they drip, making them hard to locate. The radiator side tanks are one example considering that the front of them are blocked by the condenser and thus not visible. You might borrow a cooling system pressure tester from AutoZone. Pump up the system and if the pressure drops over time, keep pumping it up. With a cold engine, any leaking coolant will eventually drip before evaporating.

    It could also be an intake gasket. That would ingest and burn the coolant so none would be seen in the oil.

    As for exhaust steam, the leak has to get pretty bad for that. I don't know if a gallon per 60 miles would be enough to show or not.

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    mmayer110 is offline Cadillac Owners Member
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    Re: Disappearing Coolant

    If it is the intake gasket, is that a difficult repair? I'm not sure where it is on this engine. Wouldn't a cylinder be scored by now if water was being burned with fuel? Or would it take a long time and have to be a bigger leak in order to do any damage. On a 1985 Eldorado I had a bad head gasket leak that stopped the car, but it did not do any damage. A new head gasket was installed and off I went for another many thousands of miles.

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    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Disappearing Coolant

    The intake manifold is what the TB is mounted on between the cylinder heads (#40). Not terribly difficult. The only thing that coolant being burned with fuel will do is steam clean the piston head, cylinder head and spark plug. It won't cause any damage. All that being said, it is after all a 4100 and they are known for HG failures.


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    mmayer110 is offline Cadillac Owners Member
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    Re: Disappearing Coolant

    Wow. Thanks for the "exploded" engine view. This should help a lot. I have not been adding coolant, so at this point if I am burning anything it is probably mostly water, which I understand does not do as much damage as coolant would do. In any case, it's good to know that I haven't scored the pistons or cylinders. I'll try to get this checked out as soon as possible. I love this car, its economy, and the fact that this particular one looks as if it just came out of the factory, entirely original.

  7. #6
    Submariner409's Avatar
    Submariner409 is offline If it won't run, stick on fender vents
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    Re: Disappearing Coolant

    Parts and diagrams - www.gmpartsgiant.com - your make, model, year, submodel, system. Opens a numbered text page. Click the "More Info" tab to open the large diagram keyed to the text page. Bookmark the site - you'll need it.

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    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Disappearing Coolant

    Quote Originally Posted by mmayer110 View Post
    at this point if I am burning anything it is probably mostly water, which I understand does not do as much damage as coolant would do.
    In this scenario (burning it in the cylinder), water or coolant is the same and does no real harm. Where coolant does real damage is when it gets into the oil. Coolant and bearings do not play well together.

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