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May 20, 2009


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Another tip if I may, If the impeller is missing blades as in the picture. Look down stream an try to find ALL the missing blades. Heat exchanger is a good place to start!


Nice article Mark. I like the ziptie and cover flip tricks, may add those to the bag of tricks. I've always used silicone grease b/c it's handy- same stuff used for dive gear. Does the glycerine hold up well for the season? Also, those impeller pullers are pretty gentle if you wish to cling to that old impeller for a spare.

The lubricant is only there to help in the initial installation and period when the pump runs at start up until the water comes through. After this time the vanes are lubricated by the water. The glycerine is water soluble and is washed out within a couple of seconds of pump running. No grease should be used that is going to stay on the vanes which may actually be damaged by grease.

Usually it is a good idea to clean the contact surfaces and remove any crud on the input side or it could break off and damage the turbine at a later date. A little silcone grease on the waterproof seal can improve things a little too..

I found this article very useful, thank you.

As ever, highly informative and very helpful! I have a Yanmar 1GM10 which is overheating. The inflow into impellor chamber seems good. I replaced the impellor which was worn but in one piece and this has not resolved the problem. It has been suggested that the cause is limescale build up which is preventing the flow of cooling raw sea water. Is this a common problem and how is it best rectified? Thanks!

Several things can cause an engine to overheat. The first would be to check and replace the impeller as you have done, the next would be to check the water flow through the engine. With the engine running there should be a good flow of water being pushed out of the exhaust as the engine runs, if not that would indicate either a blockage in the water pickup pipe or raw water strainer which must be clean and clear or a blockage inside the water galleries inside the actual engine, which is quite rare.
Check the obvious first my money would be on a restriction either in the raw water seacock or the strainer so check these initially. It is unlikely that the problem is in the actual engine itself. The last and final thing that is often overlooked is if the engine is only overheating as it is pushing the boat along there could be a lot of weed or even a bit of rope around the prop which is placing too much strain on the engine and gearbox.

Mark,thanks again for your advice. As it turned out it was indeed an obstruction caused by the accumulation of salt deposits that completely occluded part of the cooling system. A giveaway is a 'cracking' sound which can also be felt when the rubber hose components of the cooling system are squeezed. Clearly a pitfall of raw sea water and long periods of non use of the engine, although I have been careful to run it at least once a month for half an hour ...

Glad to see your article. One thing to note is that impeller pullers are pretty gentle if you wish to hold onto to that old impeller for a spare.

excellent traitement du sujet ,bravo et merci

Another common cause of an engine " running warm" often overlooked is if the boat is OVERPROPPED either by diameter or pitch.Things usually are ok at low RPM but when you open it up a bit that's when this problem occured.Got the tee shirt on that one I'm afraid learned the hard way.

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