Overheating from Fouled Heat Exchanger

Yanmar Heat Exchanger Fouling

There has been some discussion on the Yahoo List regarding overheating due to fouling of the fresh water side (antifreeze side) of the heat exchanger.  It turns out that this problem is not isolated to the C380/387.  The May 2009 Mainsheet has an extensive article in the C470 section regarding a similar problem.   It appears as a brown film, or sludge, on the freshwater side of the bundle.  The source or origin is unknown.  It had been proposed that this is a left over coating from the manufacturing process that is supposed to be cleaned during the commissioning process.  However, I discussed that theory with Richard Mastry of Mastry Engines in St.   Petersburg, who supplies engines to Catalina, and he was unaware of it.  However, he did say that captains should be careful not to over-prop so the engines run at rated rpm’s, mix antifreeze to

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3 thoughts on “Overheating from Fouled Heat Exchanger”

  1. I have experienced the same porblem with my C-387 #75. My Yanmar was running around 190 deg. F. at 2000 RPM. Unlike others, I did not have it flushed and cleaned before I made a trip to the Abaco Islands in the Bahamas. When I returned, water was leaking around the end cap. The mechanic discovered the same “crud” in the exchanger, but the water had corroded the metal away so much it could not be safely repaired. Now I have a new heat exchanger and I will be flushing/cleaning it every other year from now on. Not being the original owner, I have no idea if the P. O. had ever cleaned it. It was running at 180 deg. F. with approx. 400 hrs. when I purchased “Sabbatical” and started running at 190 deg. F. at apporx. 680 hours. It was another expensive lesson! Roger Henderson C-387 #75 “Sabbatical”

  2. Quite a few captains with Yanmar’s installed have reported a similar issue, beginning shortly after these engines were first installed on C-380’s several years ago.
    In addition to the possible cause noted in the article above, another theory relates to the antifreeze used. Some on-line research indicates that even a moderately-strong solution of antifreeze/water [50/50 is normal mixture] can cause a brown sludge in cooling systems.
    The increased incidence of the sludge issue occurring near the time of the introduction of “long-Life” antifreeze [recommended by both Yanmar and Westerbeke] may not be coincidental. One possibility is that some dealers or captains have noted the availability of a pre-mixed version on store shelves, but inadvertently purchased a full-strength container and used it that way.
    So..as with most boat projects, double-check.

  3. I decided to inspect the heat exchanger on my 2002 460 engine hours Yanmar 3JH3E after finding missing impeller blades in raw water pump — I found the missing blades in the heat exchanger & also the brown sludge. I decided to buy some radiator flushing chemicals & boiled up the bundle in them on the BBQ — this removed the hard to get at sludge for $8 & after careful re-assembly all is good & temp control is improved with cruising temp rising from 180 at 2700RPM to 182 at 3500 sustained for 5 minutes.

    Alex C380#350

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