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Difficult Overheating Problem on Inboard

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  • Difficult Overheating Problem on Inboard

    Hello All,

    I have a 2002 Supra Launch with a 350 GM (Vortec) engine (marinized by Indmar)...it's an inboard running through a V-Drive. The boat is new to us...we've had it about 20 hours worth, and just back from a trouble-free week on Lake Chelan. There is a total of 190 hours on the motor, and the previous owner had it winter-ized/de-winterized by a shop, and kept it stored in a heated barn over the winter. The boat is in excellent condition. This is my third boat...the first had a closed I/O volvo system, the second a Mercruiser I/O freshwater system. Neither of the first two were trouble free...by any means, so I've got some idea of what I'm doing...my wife says just enough knowlege to be dangerous.

    We keep the boat moored on a nearby lake. We are up in the lilly pad area, and the water isn't very deep, but we only draw two feet, so it hasn't been a problem. My son was out and noticed the temp getting up over 175, and then saw it spike up to 250-ish. The limiter kicked in and forced the engine into limp mode. He shut it down, opened the hatch, and let it cool. After it was cool, he idled it back to the dock...fortunately he wasn't far.

    So here's what I've done to trouble shoot:

    - I have access under the back seat to the transmission cooler and raw water inlet area. I removed the hose from the raw water inlet to the transmission cooler. I can blow into the hose, and I get bubbles under the boat. If I lower the hose to water line level, I get water rushing through the hose into the bilge. I re-attached the hose.
    - I removed the second hose (outlet side) of the transmission cooler, and I can blow through the transmission cooler and get bubbles under the boat. Everything is re-attached.
    - I checked the impeller. This is where I really expected there to be a problem. I removed the pump and pulled the impeller...everything looks great...the impeller looks new, no cracks. The pump cover had some discoloration on it and a little bit of scoring, so I used emory cloth on a flat surfact to clean it up. I didn't get all of the scoring off, but it cleaned up nicely. Replaced the gasket and put it all back together again. The hoses have a definite order in which goes where, so I'm confident they went back on properly.
    - I pulled the thermostat. It was rusty looking, so I replaced it. The new thermostat opens properly at temp.
    - I pulled each of the hoses from the temperature housing that go to the manifolds. When I blow into them, I get some resistance, but it blows back out the temperature housing that the hose came off of. No obstructions.
    - I have a hot water shower that is plumbed into the top hose that comes from the impeller. I pulled this (small) hose off and ran the engine. At first, It dumps a stream of water into the bilge. Then it pulses water into the bilge, at a decreating rate...than it didn't dump any water at all, it just hissed and steamed. Temp was going up so I shut the engine down.
    - I'm about 3 miles from the boat launch, and I don't relish the idea of limping the boat down to get it trailered...I will of course if I have to.
    - I have noticed that there isn't a lot of water in the hoses that go in and out of the thermostat housing. I'm at the point where I keep re-doing and re-checking the things I have already checked.

    Any suggestions would be greatly appreciated!

    Thanks,
    John


  • #2
    Re: Difficult Overheating Problem on Inboard

    Is it possible your raw water impeller sheared its key? I would break it down into small chunks to isolate the problem. For instance with the outlet hose of the raw water pump removed start the engine. Water should pump out continuously at a good rate even at idle speed. If not, either the inlet is starved because of a blockage (possibly debris stuck in the thru-hull?), or the impeller simply isn't being driven.

    If that checks out OK move on downstream from the raw water pump. Is water exiting the exhaust? If not disconnect the supply hose to each manifold or riser and see if you get flow. Maybe your risers or elbows are clogged with a buildup of rust.
    '77 Luhrs 28', had GM diesel V8 last year, now installing Mercruiser 5.7 gasser w/ 310HP!!

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    • #3
      Re: Difficult Overheating Problem on Inboard

      Check your inlet hose for soft spots, it may be collapsing under the suction.
      1946 Gar Wood
      1949 Gar Form
      1974 Century Arabian
      1978 Chrysler Mutineer
      1991 Kawasaki Jet Mate

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      • #4
        Re: Difficult Overheating Problem on Inboard

        Originally posted by Luhrs28 View Post
        Is it possible your raw water impeller sheared its key? When I pulled the pump, I lubed it with WD-40 and turned it by hand to be sure it worked...so as far as I can tell, the pump is turning.

        I would break it down into small chunks to isolate the problem. For instance with the outlet hose of the raw water pump removed start the engine. Water should pump out continuously at a good rate even at idle speed. If not, either the inlet is starved because of a blockage (possibly debris stuck in the thru-hull?), or the impeller simply isn't being driven. Ok, this makes sense. As I'm thinking about this, it's possible I'm blowing air out, but it could still not be letting enough water in.

        If that checks out OK move on downstream from the raw water pump. Is water exiting the exhaust? If not disconnect the supply hose to each manifold or riser and see if you get flow. Maybe your risers or elbows are clogged with a buildup of rust.
        I'll give this a try in the morning. I appreciate the suggestions!

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        • #5
          Re: Difficult Overheating Problem on Inboard

          I'll check that as well...I know several of the hoses were "special" solid type, but the ones coming to and from the raw water pump are standard hose material. I appreciate the help!

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          • #6
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            Re: Difficult Overheating Problem on Inboard

            OK, problem solved. I followed the (very good) advice given...here is what I found:

            - I wasn't geting much water coming out of the raw water pump with the engine running. I tracked back...inlet was fine.

            - There is a hydraulic line cooler that sits on the raw water line between the V-Drive and the impeller. It's tucked under the manifolds, and you have to dis-assemble the rear deck to get to it. When I blew into the hose on the impeller side, it bubbles under the boat...line is clear. When I took the hose off the inlet side of this cooler, I found that it was filled with silty beauty bark size chunks of wood debris. So when I blow in the reverse direction to the flow of water...they push out of the way of the screen on the cooler unit. When the water reverses this, they slam into the screen again, blocking the flow. So cleaning the cooler out fixed the problem. Sheesh.

            Lessons learned: methodical testing of each component in the line works. Sporadic testing, not so much. Check the water flow in the direction of the water flow. Know your boat...especially the things that are hard to get to, like water inlets, while it's out of the water. I had to do the snorkel thing to check my inlet at 6am this morning, to be sure I didn't have a blockage of some sort there. It would have been a lot easier if knew what it looked like...on the trailer. Buy the manual ahead of when you need it...they aren't available when you are in a hurry. Ditto for the impeller.

            Thanks again for all your help!

            John

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