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Old 08-29-2015, 08:51 AM   #15
twistedtree's Avatar
City: Gloucester, MA
Country: USA
Join Date: Jan 2013
Posts: 4,448
Sometimes it's hard to see your own black smoke. If you can, have a buddy observe while you are running WOT.

At WOT, your engine should EXCEED 3200 RPM by 50-100 RPM. If it doesn't, you are over propped. Many people will tell you that's fine as long as you limit your power level at any give RPM, but I don't think most people have the discipline to do that.

Your trans issue is interesting - not sure what to say about that, but if it's working OK now I'd set that aside and stay focused on the other problem.

If you are over propped, it will contribute to high operating temps, but probably isn't the sole issue. It sure sounds like you have some limitation in your cooling system.

Probably the best thing to do is go through the cooling system from end to end and bring it up to snuff. I would focus on the raw water side, so start by making sure your intakes are clean and clear, and strainer is clean and clear.

Then open up the raw water pump, check the impeller, and replace it while you are in there. You might find that a few fins on the impeller are missing.

Then give the heat exchanger a good inspection and cleaning. You could have build up in the tubes that will restrict water flow and inhibit heat transfer. You can clear the tubes with a dowel or other such tool. Also check inside the cooler on the end where the raw water enters, and be sure there aren't any impeller parts bobbing around in there. When they break off the impeller, they will often get stuck in there rather than getting flushed through, then they block water flow.

Next take off the exhaust elbow and sprinkler and inspect it really carefully for corrosion, perforations, etc.

If the engine had an after cooler, that will need to be services too, and typically involves removing it from the engine, disassembly, cleaning, greasing up the mating joints, new o-rings, and a pressure test. Any salt water leakage from the raw water side to the air side will result in pretty much sudden death for the engine as it ingests salt water.

Based on your gear experience, it sounds like the power plant was not well maintained, so I think gogin through everything will be well worth while, and allow you to establish a good base-line for future maintenance.
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