My new 3YM30 overheats

[chesapeakesailor]

I had the same problem and yanmar replaced the cooling bundle free of charge since it was quote "a new design" for them, and was insufficient under certain (often standard) cruising conditions. Ask them to replace it for you under your warranty, with their "other design" bundle. Which basically has more tubes in the coil allowing for more efficient cooling. Good luck!

[chuck711]

Simply they engineered the heat exchanger incorrectly. They reduced the number of cooling tubes by 40%. There is a warranty
program to correct this however it is not advertised.........

[chuck711]

I think you'll find that they reduced the number of cooling tubes on your orginial Yanmar Engine and they corrected the problem when they replaced the heat exchanger. They doubled the # of cooling tubes.
Engineering problem.