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Overheating at Close Quarters-gctid350435

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  • Guest's Avatar
    Guest replied
    BTW...thanks to everyone for helping with this!!!

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  • Guest's Avatar
    Guest replied
    dmcb wrote:
    Could be. Now lets go back. You said you knew the coolant tank was low quite often and you fill it. You ask for suggestions. No one suggested you check your coolant to see if it was low.

    Now it was an assumption for me and I imagine others that you would have checked to see if the coolant was low.

    It seems you didn't do that basic thing as all you have really done is add coolant. And stopped the leak.

    We all learn something here. For us, don't assume anything. For you, check the basics meaning simple things first.

    Glad you found it and I hope it is then end of your problems.

    Doug
    Actually if you look above you will see I said in my first post:

    "One thing that mystifies me is my coolant overflow tank is low...I fill it up a bit...and she ends up low again. Can't see any leak in the bilge so no idea what's up there."

    Because of the placement of the coolant tank (not the overflow) I can't actually look into it. or wrench my head back there. I never saw coolant in the bilge (also never saw drips or drops anywhere)...that was the first thing I actually checked the last time this happened, but could not see any evidence of a leak.

    I had a mechanic in there not long ago and all my hoses and clamps were checked and tightened. If you don't see a leak and you don't see evidence of a leak and even if you feel around and don't find anything...you may not run across a leak. What I think was likely happening (which is why this was masked a bit) is that underway the leak likely increased, but sitting in a slip, was slow to nothing. The reason I discovered it was because of other's suggestions here and doing a second check myself of all hoses and connections and tracing everything back. It was checking that hose path to the thermostat that helped me run across it.

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  • Guest's Avatar
    Guest replied
    I had a similiar situation where my boat would overheat at idle rpm and then overheat at high rpm but would be okay in mid rpm operation. These conditons were both the cause of low antifreeze in a closed cooling system. I thought I had a leak and frantically looked for it, I traded exchanger caps up to 16lbs. I was still losing antifreeze at a rate of 1/2 quart on a good days run. It was going through the overflow hose into the bilge but not at a rate that you could really notice. I finally installed an overflow resevoir with the middle of the bottle level with the top of my exchanger. Now the antifreeze is captured and returned when it cools down, that solve all my problems completely. No more loss of antifreeze or overheating. My boat did not come wth a factory overflow resevoir. I tried to buy a Mercruiser overflow WOW $$$ so I ended up grabbing one in good shape from an old Dodge truck that was a little larger then the Mercruiser. Saved myself $60 and haven't had to add any coolant for years, just maintenance flushes for me now.

    I should also add it is easier now to know your coolant level without taking off the cap; just look at the overflow it should be half full.

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  • dmcb
    replied
    agraham999 wrote:
    Okay I tightened her up, topped off the coolant tank, ran her for 15 minutes...high rpm and low...she never goes up above 150 on the gauge...plenty of room before the red...when I did this the other day the moment I took the rpm down she's spike in heat. So I'm guessing that when I'd head out...I'd run low on coolant...and the raw water at a higher rpm kept the engine cool but at a lower rpm the other coolant wasn't enough...

    Does that sound right?
    Could be. Now lets go back. You said you knew the coolant tank was low quite often and you fill it. You ask for suggestions. No one suggested you check your coolant to see if it was low.

    Now it was an assumption for me and I imagine others that you would have checked to see if the coolant was low.

    It seems you didn't do that basic thing as all you have really done is add coolant. And stopped the leak.

    We all learn something here. For us, don't assume anything. For you, check the basics meaning simple things first.

    Glad you found it and I hope it is then end of your problems.

    Doug

    Leave a comment:


  • Guest's Avatar
    Guest replied
    so do I...I'm going to judiciously watch it though...especially underway.

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  • Guest's Avatar
    Guest replied
    I'm hoping its not a crack either. It took forever to diagnose; and I ended up removing the manifold as a last resort. If you suspect that leak was a slow one and responsible for depleting your coolant, keep a constant eye on coolant levels. Hopefully, you caught the problem.

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  • Guest's Avatar
    Guest replied
    I found the leak around the elbow joint you see above, where it screws in...I tightened it up...it was loose. I think the reason I may not have seen any coolant is that it's such a slow leak that it slowly ran out (very slowly) and into the bilge and mixed with the other water in the bilge. I also think that the overall coolant levels were really low, but as I'd top it off, it would run fine awhile.

    I would hope it isn't a crack though...this is a new engine with only 300 hours on her.

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  • Guest's Avatar
    Guest replied
    You mentioned there was no coolant in the bilge. If this is in fact a leak, wouldn't you see it in the bilge. My concern would be around where the coolant is actually going. On my previous boat, I discovered one of the walls of the manifold had developed a crack; and the coolant was going into the exhaust stream. I would run the engine for 15 minutes and a third of my coolant would disappear. Check to see whether this is the case. You don't want to be losing coolant, even in small amounts. I eventually replaced the manifold and the problem was solved.

    As to whether that happened at slow RPM's, I don't think it made a difference for me.

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  • Guest's Avatar
    Guest replied
    Okay I tightened her up, topped off the coolant tank, ran her for 15 minutes...high rpm and low...she never goes up above 150 on the gauge...plenty of room before the red...when I did this the other day the moment I took the rpm down she's spike in heat. So I'm guessing that when I'd head out...I'd run low on coolant...and the raw water at a higher rpm kept the engine cool but at a lower rpm the other coolant wasn't enough...

    Does that sound right?

    Leave a comment:


  • Guest's Avatar
    Guest replied
    [img]/media/kunena/attachments/vb/654311=24661-photo3.jpg[/img]Feeling around I just found a leak off one of the hoses from the thermostat...this is the antifreeze/coolant side...I said up before that sometimes the overflow would have fluid....and then be empty...so what if the engine is simply low on coolant? I just never noticed this leak before because is was so slow.

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  • Guest's Avatar
    Guest replied
    I would check exhaust manifolds and elbows. When the rust up they can be OK at speed and not let enough water through at idle.

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  • boatworkfl
    replied
    Check the strainer, back flush it if possible in case the pick up strainer is clogged, check the thermostat, it may not be opening at the proper temp.

    Check the exhaust at the riser exit for rust.

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  • Guest's Avatar
    Guest replied
    I pulled out the impeller and it looks brand new...any other thoughts?

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  • Guest's Avatar
    Guest replied
    So I started following the hoses from the intake which all had water coming in fine. I then opened the impeller, but I'm not experienced with these so I don't know if this looks good or bad. She's rubber...this look like it's a problem?

    [img]/media/kunena/attachments/vb/654295=24659-photo.jpg[/img]

    [img]/media/kunena/attachments/vb/654295=24660-photo2.jpg[/img]

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  • dmcb
    replied
    With a water pump impeller that is bad it will still pump water. The faster it turns the more it will pump. Coupled with the fins that can still be in the system slowing down the flow, what is happening to you is what happens in these conditions.

    Doug

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