Yacht Cooling Systems

Published: 20th October 2009
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The majority of yachts with inboard engines are built with fresh-water cooling systems. These fresh water systems in conjunction with the raw water system cool the engine during operation. The fresh water circulates within the engine and transfers the engine heat to the raw water system as it passes through heat exchangers. This article will explain the step by step approach to servicing your yacht's raw water cooling system.

Over time, the raw water system on a boat will become clogged with calcium carbonate, usually called scale. This scale will create troubles for your engines. Heat exchanger cooling tubes and piping will become completely blocked if left unchecked.

So how does this occur you ask? When hard water comes in contact with heated surfaces, the minerals in the water fall from suspension. Those minerals, mainly calcium, attach itself to metal surfaces inside heated component parts on the boat. The same thing occurs inside hot water heaters.

Become familiar with your engines

Prior to servicing the engines on your used trawler, motor yacht, sailboat or cruiser, it is critical that you take some time to acquaint yourself with the raw water cooling system of the engines. Get drawings and parts diagrams if at all possible. Study your engines and trace the raw water flow from the intakes to the discharge. Make a mental note of each component.

There are two methods to overhaul your used boats engine.

Method 1 - Completely Disassemble the Cooling System

With your part's manual close at hand, take apart each component of the raw water system. You are going to need new seal and gaskets when you reassemble so keep a count of what you will need as you take things apart. Each engine is different but you will have a raw water pump and impeller, a primary heat exchanger and likely transmission and oil coolers .

Clean the cooling system

After the sections have been removed, each section must be examined. Coolers and exchangers will likely have scale built up within them. A professional radiator shop can clean these for you but a cheaper way is to mix a 4-1 solution of Muriatic Acid and water. Immerse the components into the solution and allow it to "boil" until all activity is complete; your components will be clean. Use care to protect your eyes and skin as the acid is very hazardous.

Put your system back together.

When your parts are clean, its time to put everything back together using new seal and gaskets where necessary. And you if find rusted bolts and nuts, it is a good idea to replace those too. Now is a good time to replace the impeller too.

Test for leaks and proper operation.

When you are refilling your engine with anti-freeze, be sure to bleed the system of trapped air. The method to use will be in your owner's manual. Following the re-assembly, the only thing left to do is start the engine and check for leaks.

Method 2 - Clean in Place

Using this method, you want to inspect your engine and locate the raw water pump on your engine. Locate the "intake" for the raw water system downstream from the raw water pump; here is where you will want to connect a supply hose. On my diesel engines, I have a hose that runs from the water pump to the oil cooler that I can temporarily remove. Next, locate an outflow from the water system where the cooling water leaves the engine. On my Volvos, it is after the transmission coolers.

Assemble the following:

1. - 50 gph bilge pump

2. - About 20 feet of wire to plug in the pump to your batteries

3. - A 5-gallon pail

4. - About 10-15 feet of hosepipe sized to fit connectors

5. - 1 gallon of Ph-Ospho-Ric (Home Depot paint department) phosphoric acid

Connect a part of the hose to the bilge pump and the other end to the "intake" you have located.

Place the bilge pump into the bucket and fill ½ full with water and ½ of the Ph-Ospho-Ric. Connect another piece of hose to the outflow on the engine and route back to the bucket. You'll want to remove the engine zincs and plug the holes. New engine zincs should be installed when complete.

What you now have created is a "closed loop" where the acid can be circulated through the engine. Start up the pump and begin the circulating of the acid in the engine. The water will turn a dark gray and bubble as it neutralizes the calcium deposits. You may want to add some more acid as you proceed.

Finally, after you are confidant the deposits are cleaned out, reassemble the engine, install new engine zincs and start the engine to flush the remaining acid. You are all done.

Mike Dickens, the author, is a boat owner and owner/Broker of Paradise Yachts in Florida USA.

Paradise Yachts offers used quality yachts to customers worldwide.

Visit the Paradise Yachts website to view our selection of Used Trawlers, Used Motor Yachts, and Used Sailboats for Sale

National and international sales. We ship Used Yachts and Used Boats worldwide. Located in Florida, USA. 904/556-9431

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