Overhaul Raw Water System

Overhaul Raw Water System:
05/10/13: Completed all tasks.

  1. Tools required:
    1. Intake filter gasket.
    2. Impeller gasket.
    3. Impeller.
    4. Zincs for the heat exchanger.
    5. Hose clamps for the hoses and heat exchanger.
    6. Prestone coolant (Check type and quantity with manual.)
  2. Overview.
    1. The engine is cooled with oil and coolant circulating through the engine. A separate salt water cooling system then cools the fresh-water coolant through a heat exchanger. This system ensures no salt water will ever touch the engine internals. The oil flow is circulated by an oil pump in the engine. The fresh water coolant is circulated by a fresh water pump in the engine. And the salt water is circulated with an impeller pump attached to the engine.
  3. Drain coolant. (For removal of the heat exchanger later.)
    1. Need more info.
  4. Remove raw water cooling hoses and hose clamps.
    1. Close through-hulls first.
    2. Use a propane torch to help loosen the rubber hose.
    3. Mark the hoses to note the replacement location.
    4. The hoses cost about $10 per foot and should last a long time. Years?
  5. Clean intake filter.
    1. Remove the wing-nuts and cap from the intake filter.
    2. Remove the metal filter and place in a bucket to be used for the acid soak later.
    3. After soaking (See below), replace filter, add new gasket (try Maguire Bearing Co in Honolulu), and tighten wing-nuts.
    4. The wing-nuts should be just tight enough to squeeze the gasket. We’ll check for leaks after reassembling everything and adjust as necessary.
  6. Inspect and/or replace the impeller.
    1. Remove the impeller cap and the 4 screws.
    2. Use the impeller pulling tool to remove the impellor.
    3. Inspect for damage and replace if necessary.
    4. Scrape the cap and engine surface clean to remove the old gasket.
    5. Install the impeller using no grease. A dry impeller will more readily flop the rubber arms in the correct direction with minimal wear before the raw water arrives.
    6. Replace the gasket with a thin, fiber gasket. The gasket can be easily tapped and cut out of a sheet of gasket material from Napa Autoparts.
    7. Reinstall the cap and screws. (Or soak them with the heat exchanger first, if corroded.)
  7. Remove and prepare the raw water/fresh water heat exchanger.
    1. Remove the two hose clamps holding the heat exchanger onto the engine.
    2. Slide out the exchanger.
    3. Remove all the plugs, zincs, and caps to prepare for soaking and place in the bucket with the metal intake filter.
    4. Scrape out as much foreign matter as possible.
    5. Test the exchanger by pouring water into the ports and ensuring the water freely exits the correct port.
  8. Soak the metal parts in acid.
    1. Fill the bucket with 1 part 18 degree Baum muriatic acid, 3 parts fresh water.
    2. Add the metal parts to be cleaned.
    3. Agitate the mixture to get the air bubbles out of the solution as needed.
    4. Continue until the fizzing stops and the corrosion is gone. (Should take about 15 minutes soak.)
    5. Don’t soak excessively or the metal may be damaged.
    6. Thoroughly rinse the parts is fresh water to remove all acid.
    7. Replace the two zincs in the heat exchanger and reassemble.
  9. Reinstall the heat exchanger, hoses, hose clamps, filter, gaskets and coolant.
    1. All important connections should have two hose clamps.
    2. Open the valve and check for leaks.
      1. The filter wing-nuts should be just tight enough to prevent leaks and may need to be tightened a bit.
  10. Test the engine.
    1. Verify oil pressure as usual and water should start spitting out the exhaust after a few seconds. If not, shut it down and investigate. It’s probably the shutoff valve or the impeller.
    2. Check the entire system for leaks at various rpms.
    3. Also check for forgotten items, loose hose clamps, etc.


Check zinc size for your heat exchanger.

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