It really seems like a head gasket job. If the engine has had a head job in the past then the problem may have been that the normal follow up head bolt/nut tightening may have been neglected. This secondary tightening is usually carried out after some nominated period of engine operation. Check your service
manual. (25 hrs ?) However, once water secretes under the gasket, then it's usually too late and the gasket should be replaced and the two surfaces checked. Removing a head gasket requires care and the use of a vacuum cleaner to prevent any bits of the scraped off gasket material from falling into the engine cooling
galleries or the con rod holes.
Some engine manufacturers don't encourage the use of gasket sealants but Hylomar is a typical product. You will need a good torsion gauge wrench. Measure the torsion values when removing the head (see manual for correct sequence). These values should be near identical. Discrepancies may reveal the nature of the problem. Follow the correct sequence when replacing the head.
Removing and assessing an engine head is usually a job for professionals as they can do assessments of the valve seats and the head surfaces and can carry out the repairs
in specialised workshops. Plus you should get a warranty. Not cheap
, particularly for Yanmar parts
, but well worth it.
Regarding the anodes: yes, they do need very regular replacement. They are there to protect the cast iron engine block interior
surface. They do nothing for the outside surface though as an electrolyte such as salt water
is required on the surface to be protected.
Another issue is the thermostat. (Expensive!) but they should be checked regularly as well. Particularly if there is any rubbish in the water.
A common practice for these direct salt
water cooled engines is to ensure fresh water flushing
after use. Run until the exhaust
water is fresh, not salty. This entails a bit of plumbing
but it can really make a big difference to longevity. Most engines spend 99% of their life just "resting" but with salt water in the block, the corrosion does not stop. You may even consider a method of draining water from the block after the engine has cooled down. There may be an issue with the thermostat. Food
I have an ancient 1GM used as a genset and for running various compressors/pumps and have recently had the head done. Although not really familiar with the 2GM
I would be doing a thorough check on the exhaust
manifold as well. There are better alternative products.