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  1. F

    Ran fine last fall, now overheating. Need ideas

    I just hoping I could find some clues. I am a pretty decent boat mechanic, but this one really had me stumped. I think maybe someone put a hex on it. 😉
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    Ran fine last fall, now overheating. Need ideas

    No solid answers, but it seems to be working OK now. I put in two new thermostats, along with new spacer rings. I drilled two 3/16" holes in the thermostats to make sure no air could get trapped. I also put the garden hose on every discharge hose. All seemed to be free flowing. Used an air hose...
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    Ran fine last fall, now overheating. Need ideas

    Manifolds are aluminum with stainless risers. I ran a garden hose through the exhaust cooling passages and there didn't seem to be any restriction. I am going to put it all back together this afternoon after flushing everything possible, with new stats and see what happens.
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    Ran fine last fall, now overheating. Need ideas

    Trying not to sound like a dick, but all the info you are asking for is in the original post. As far as the braided hoses, all Mercury Racing 500 HPs cam with the braided lines. As far as the GLM thermostat housing goes, it is a stock replacement. I do appreciate any constructive ideas.
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    Ran fine last fall, now overheating. Need ideas

    That is my assumption, but there seems to be plenty of water coming out of the exhaust pipes. The boat is in the water. I don't ever run it very long on the hose.
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    Ran fine last fall, now overheating. Need ideas

    Removed hoses, ran garden hose through all exhaust passages. Balls are free and look normal. Winterize using rv antifreeze pumped through running engine.
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    Ran fine last fall, now overheating. Need ideas

    Here is a picture of my thermostat housing. I know it has the spring loaded balls in the brass tee fitting
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    Ran fine last fall, now overheating. Need ideas

    I'll get a picture this afternoon
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    Ran fine last fall, now overheating. Need ideas

    It is very strange that both engines are doing the same thing. The water pressure gauges are mechanical, so that rules out electrical, at least for the WP gauges. I am going to try and flush the system out with a garden hose attached directly to the exhaust manifold water lines. If that doesn't...
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    Ran fine last fall, now overheating. Need ideas

    The engines are 500HP's which are the blue Mercury racing 502's. Ran the boat last fall, everything was fine. First time out this year the high temp alarm went off. I changed stats and still having temp issues. There are a couple other strange things going on. The water pressure on both engines...
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