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  1. #1

    Default 1992 Mariah overheat then got water in cylinders

    Yesterday my overheat alarm went off on our way back home. I stopped and shut the boat off of course, but when I did there was a gurgling sucking sound for a bit I never heard before. During the teardown of my raw water pump only to see that the impeller was fine I pulled the thermostat to see that the it looked like an archaeological discovery. I assume it stuck closed and caused my issue, but I will verify today with a pot of boiling water. Could be an air sucking issue too, and I will rectify that as well. However, the starter would move the engine but wouldn't turn it over. I knew better than to keep trying and pulled the spark plugs before turning it over again. It blew water out of at least 4 holes which confirmed my suspicion. My question is how did that happen!? What failed in method or system that caused my boat to suck water up the exhaust into the cylinders? How do I prevent this from ever happening again? 351 PCM carb'd engine btw.

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    Last edited by JSPulliam21; 08-18-2019 at 01:00 PM.

  2. #2

    Default

    Well it starts after getting all the water out of the cylinders. Quite a bit ended up in the oil. About to head to the river and see if the raw water pump sucks and keeps her cool without a thermostat. Hopefully skidim can get me the right one before next weekend.

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  3. #3
    Join Date
    Apr 2018
    Posts
    150

    Default

    I am confident the water came from a blown head gasket due to overheating if you are lucky.

    Worse case is a cracked cylinder and or head.


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  4. #4

    Default

    Well that sucks.

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  5. #5

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    I guess a compression check is in order rather than a river test.

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  6. #6
    Join Date
    Jul 2007
    Location
    Flowery Branch Georgia
    Posts
    2,742

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    When you overheat on the water and shut down the engine it will create a vacuum in the exhaust and suck the water into the exhaust manifolds and through the open exhaust valves into the cylinders. First find out what caused the overheat . The head gaskets may not be bad.

  7. #7

    Default

    Quote Originally Posted by michael hunter View Post
    When you overheat on the water and shut down the engine it will create a vacuum in the exhaust and suck the water into the exhaust manifolds and through the open exhaust valves into the cylinders. First find out what caused the overheat . The head gaskets may not be bad.
    Michael I'm fairly sure a stuck thermostat and possibly an air leak in the raw water line caused the overheat. We didn't overheat on our way out for the day, but on our way back. All we did was ride out to a spot, anchor, and then ride back a few hours later. Thermostat pic attached for reference. I pulled and twisted on the crunchy grungy thermostat before putting it in a pot of hot water, because I'm fidgety I guess and couldn't leave well enough alone. The thermostat operated correctly (began opening about 145*) in the pot, but who is to say it would have before i messed with it. The impeller and raw water pump are in good shape.The hose ends on the raw water pump inlet and trans cooler inlet were in rough shape so I cut them off clean and got a much better seal. I didn't realize how bad they were. I will do a compression check tonight after work with fingers crossed.

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  8. #8

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    Compression test results engine cold and plugs out.

    1) 135
    2) 145
    3) 145
    4) 145
    5) 135
    6) 140
    7) 130
    140

    10.4% variation, but nothing seems wrong to me. Thoughts? I would think a blown head gasket would show up as a dead duck.

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  9. #9
    Join Date
    Apr 2018
    Posts
    150

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    Blown head gasket won’t always show with a compression test. On a car you would do a cooling system pressure test, but would be tricky on an open loop system.


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  10. #10
    Join Date
    Jul 2007
    Location
    Flowery Branch Georgia
    Posts
    2,742

    Default

    Buy some cheap oil and oil filters change oil and filter run for a few minutes and change it again. It may take 3-4 times to flush the oil out . Then put your normal oil and filter and give it a try. Keep an eye on the oil and make sure its not water contaminated. If you get water again pull the heads.

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