Sailboat Engine Secrets - Change Your Impeller to Keep a Cool Engine!

Figure 1
Captain John Jamieson
When was the last time you checked your sailboat engine raw-water impeller? It's one vital part that keeps your engine cool and happy all season long. In this article, John Jamieson (Captain John) of SkipperTips.com shows you how to make this task simple and easy as 1-2-3:

Your raw water pump draws water from the sea, through the sea-water strainer and up to the engine. In small diesel engines with separate fresh water systems, sea water provides a cooling jacket to lower internal temperatures. In straight raw-water cooled engines, you need every bit of that sea water circulation to keep your engine cool and happy.

Follow the raw water hose from the seacock, through the strainer and up to the front of your engine. Here, you will see the impeller pump cover (see photo of impeller pump). Marine diesel engine guru and author Peter Compton recommends that you follow these steps next along with the illustrations:

Remove the Old Pump.
Follow the raw water hose from the seacock up to the raw water impeller cover plate. Locate the pump on the front of your engine.
Yanmar Marine (n/a)


1. Remove the cover, cover plate and gasket (or O-ring). Look at the vanes and note which way they bend (left or right).
2. Pry off the central plug that holds the vane into the housing.
3. Use two flat-head screwdrivers to carefully pry out the impeller pump. Take care not to damage the vanes.

Inspect the Pump and Pump Parts.

1. Check all around the vanes for cracks, hardening, wearing or melting.
2. If you notice missing chips of rubber, this means particles of rubber impeller could have lodged themselves in the heat exchanger inlet. Follow the hose from the impeller up to the heat exchanger (see bottom photo). Pull off the hose and remove all particles before you start the engine!
3. Check the cover plate for wear (scoring). This reduces your pumps efficiency. Replace the cover plate if scored.

Install the New Pump.

1. Lubricate the new impeller pump with silicone grease or soak it in water.
2. Place the pump into the housing so that the vanes rotate in the same direction as before (you did check this, didn't you?). Replace the plug to hold the pump in place.
3. Install a new gasket or O-ring. Soak the gasket in solvent first to remove packing grease. Lubricate an O-ring with a light grease. Replace the outer cover.

You will keep your sailing boat's diesel engine roaring like a lion when you change your raw water impeller once each year. Follow these simple sailing tips above to add life to your engine and save money in expensive repair costs--wherever in the world you choose to cruise!

John Jamieson (Captain John) teaches sailing skippers the no-nonsense cruising skills they need beyond sailing school. Sign up for his highly popular FREE sailing tips newsletter at http://skippertips.com Become a member for instant access to 425+ articles, video tutorials, newsletters, and free eBooks.
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