I helped a friend of mine bring a new to him Cal 25 from Munro Michigan to Port Stanley last year. He had a borrowed Mercury outboard which he freshened up with spark plugs, raw water impeller, and I don't remember what else. He also tested it out both in a barrel and on the boat when we got over to Michigan.
We left Munro, no wind, and about an hour out into the channel the motor started to falter and after a few starts and stops we hauled it aboard and disassembled it in the cockpit. Since the exhaust exited underwater, it was not immediately apparent to us that the problem was the cooling system. To make a long story shorter, the new impeller had failed by the rubber coming unstuck from the brass centre. It was a brand name part, and not a knock off. Never expected that sort of failure, and I don't know how you could protect against it except by keeping a spare on board, perhaps of a different manufacture date. Steve Thomas C&C27 MKIII Port Stanley, ON -----Original Message----- From: CnC-List [mailto:cnc-list-boun...@cnc-list.com]On Behalf Of Rich C&C Sent: Friday, October 19, 2012 10:46 AM To: cnc-list@cnc-list.com Subject: Re: Stus-List Miscellaneous -impeller This is an interesting topic as there are many variables that may affect the condition of the impeller. My Yanmar 3QM30 engine typically accumulates a maximum of 100 hours of operation in a sailing season. On most daily outings, the engine runs approximately 15 minutes at each end of the excursion. I have an hour meter and keep track of oil changes and other maintenance items with a reasonable degree of accuracy. Major servicing of filters, oil change, impeller check, etc. is done at winter layup so the engine sits for 5-6 months with clean oil. I also make sure the cooling system has been well flushed with fresh water before starting the winterization process. The current impeller has seen 7 seasons of use and will remain in place for next season. The boat operates in relatively cold North Atlantic salt water which is generally clean and results in little accumulation of weeds or anything else in the raw water filter. The engine is raw water cooled and during the just completed teardown and rebuild appeared to us to have little corrosion or build up in the block and head. The cause of the excessive blow-by which precipitated the rebuild remains undetermined, but could not be related to insufficient cooling. The impeller, a crucial component, appears to suffer little annual wear and has never catastrophically failed. Perhaps warmer water, higher levels of silt or chemicals, or significantly greater use may have a greater negative effect on and impeller. I have had a number of outboard motors with varying experiences with impellers, most of the negative ones were related to sand intake and salt deposits that were not flushed out properly before storage. Outboards I have owned in fresh water areas have run for years with no impeller problems. As a last comforting thought: if the impeller fails and the engine cannot be run, sails are a fine backup system. Rich Knowles INDIGO - LF38 Halifax, NS From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of honeys...@aol.com Sent: October 19, 2012 10:27 To: cnc-list@cnc-list.com Subject: Re: Stus-List Miscellaneous -impeller Spend a few bucks and change the impeller with each annual service, the few dollars that it cost will save you grief & money in the end. A senior Yanmar factory tech told me that after a year of two the rubber blades on the impeller will "set" and will decrease in efficiency due to fatigue in the rubber, the blades may not indicate cracks but you can bet they they have lost some flexibility. The Yanmar guy is a good friend & was not trying to me impellers, just offering good advice.... The choice is yours, but if you want go longer than 2 years you may want buy a Sea Tow package... Jack Fitzgerald HONEY C&C 39 TM Savannah, GA
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