I have just seen the following post on a different forum and would like to bring it to your attention. The post refers to what has happened in UK, obviously I have no knowledge of other countries:
"Approximately the first 5,500
Yanmar 3YM30 diesels supplied to boatbuilders and fitted in Jeanneaus and US-type Hunters (amongst others) have an
overheating problem, usually showing up only after about 100/150 hours running, and when the sea
water temperature rises in summer. On my
engine the
overheating warning light/beeper was going off, and a check by an
engineer with a temperature guage showed the
engine was genuinely overheating, not just having an over-sensitive warning light
sensor.
Yanmar and their distributors in the UK, EP Barrus, know of this problem, and are fixing it under warranty. However they are NOT warning users in advance of this known problem. They also appear not to be even telling their
service dealers about this - the first my local dealer knew was when I told him - I found the first
references to this on the web relating to US-marketed Jeanneaus.
Fortunately I found the problem on my engine (in a 2005 model Sun Odyssey 35 with 90 hours) before departing on a longish
cruise, and it was fixed just before departure. I met up two days ago with another owner of a similar
boat who had to delay his
cruise west mid-holiday while the Weymouth Yanmar dealer got the
parts and did the fix on his engine (at 125 hours).
These early (2004/2005) engines have a 38-tube
heat exchanger, and some very early engines were reportedly also fitted with a smaller capacity
water pump">raw water pump than is now used. The fix is to replace the original 38-tube
heat exchanger core with a new 63-tube one, and change the
water pump if necessary.
If you have a Yanmar
3YM30 with an engine
serial number under 6,000, I suggest you
phone EP Barrus and ask if your engine is affected. I am not sure of the exact number of the last of the faulty batch, but Barrus know. Don't rely on your Yanmar dealer having just serviced the engine to know about this!"