Extended life anti-freeze.
Yanmar is recommending the exclusive use of the Extended Life Coolant/Antifreeze. They also recommend changing it every two years. I have a jug of Havoline ELAF before me that says its warranted for five years or 150,000 miles. I questioned Yanmar about the frequency of change and they tole me it was because of the harsh marine environment. I can't see how that antifreeze knows that it is not tooling around inside some Cadillac, all closed up inside that engine - I'll never tell it. The ELAF is not considered environmentally friendly. It must be disposed of properly when changed. A 50/50 mix is good. It brings the freeze protection to -34F, more than needed, and it takes the boiling point to 265F. You mention using an environmentally friendly product for your internal coolant. There is something in my grey cells about it but I would like to know more. Can you respond with some info?