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post #29 of Old 08-05-2013
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Re: Confused about which oil weight to use

Drifting off subject a little, but to revive the old debate about whether to convert a raw water engine to fresh cooling is worth the money.
Personally, I don't believe it is. Raw water cooling is simple and cheap. The key to long engine life is frequent use and flushing with fresh water prior to any lay-up. If you are not using the engine frequently, a fresh water flush every time you shut down would be a good thing to consider. Because they don't run as hot as fresh water cooled engines, they may wear a little faster, but hey, just how many hours are we talking about over, say, a 15 year life?

Fresh water cooled engines still have salt water coming in to the heat exchanger and being discharged via the exhaust, so corrosion will occur in those components anyway. Heat exchangers usually have zincs to replace, just like those in the block of the salty engines. Heat exchanger tubes get salt-encrusted and weed in them, just like their salty mates. The difference in engine life might be 15 years for the salt (which I achieved with a Yanmar 2GM and it was still going strong when I sold it) and 20 years for fresh. Plus more hoses and another pump to deal with, and possible heat exchanger replacement at the 10-15 year mark anyway, so would the additional cost of purchase and maintenance be fully recovered in that time span? About break evens whichever choice you make, I guess.

Sure, if buying a new engine, I would consider fresh water cooling if I thought that I would be keeping the boat for more than 15 years. My current 2GM is now 6 years old and there is at least another year in the original exhaust elbow - thanks to continuous summer use and end of season fresh water flushing.
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