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  1. #1

    Default Oveflowing coolant reservoir

    I have a 1974 318 FWC engine with a coolant reservoir that overflows everytime I run the engine. I have put an empty juice on the overflow hose to catch the coolant and reuse it, but a day long usage will run the reservoir dry. The coolant is clean and not discolored by oil, exhaust, or rust. I have tried a few new caps with no success. I don't know that it matters, but this engine also has the hoses sending coolant to the cabin air heat exchanger.

  2. #2
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    16,194

    Default Re: Oveflowing coolant reservoir

    Bad pressure cap?

    Jeff

  3. #3

    Default Re: Oveflowing coolant reservoir

    I have tried three caps, including swapping the one from the other engine. No change.

  4. #4
    Join Date
    Jan 2011
    Location
    North Lake Tahoe and Delta
    Posts
    245

    Default Re: Oveflowing coolant reservoir

    With the cap off and the engine running are there bubbles in the tank?

  5. #5

    Default Re: Oveflowing coolant reservoir

    No bubbles, but I can watch the coolant rise in the cap neck as the engine warms.

  6. #6

    Default Re: Oveflowing coolant reservoir

    Check your heat exchanger for internal leaks. Maybe its leaking sea water into your coolant, thus increasing the fluid level and creating the overflow.

    -JJ

  7. #7

    Default Re: Oveflowing coolant reservoir

    I don't think think the raw water side operates at a higher pressure than the fresh water side, but I guess it could. I also have two year old exhaust manifolds and boiled out and checked the heat exchanger at the same time. They run fluid pretty freely now.

    I'm thinking I could have a stuck thermostat and fluid from the cabin heat exchanger is overfilling things before it can open. I'll check that first. Maybe rerouting lines is in order, or finding a thermostat for the heat hoses.

  8. #8
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    16,194

    Default Re: Oveflowing coolant reservoir

    You might also try a pressure tester (borrowed from Auto Zone) to see if you have any leaks.

    Sorry to say it, but you might have a head gasket going--that would cause that. If the pressure won't hold with the tester, pull the plugs, wheel her over, and look for coolant coming out. (You'll need a couple of sharp-eyed helpers for that.)

    Hope that's NOT it.

    Jeff

  9. #9

    Default Re: Oveflowing coolant reservoir

    Quote Originally Posted by Kevinde View Post
    I don't think think the raw water side operates at a higher pressure than the fresh water side, but I guess it could.
    It could if your fresh water side was no longer a closed system (a.k.a internal leak). Keep in mind that the fresh water side operates under pressure due to heat in a closed volume. If that volume is now open due to a leak, you'll lose pressure in the system.

    -JJ

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