Owner of 3 GMC (raw water) for 28 years,
Cold starting: Yanmar recommends lots of throttle, as much as 3/4
then upon starting throttle down.
Rydyme flush: follow directions...upon completion must neutralize
Rydlyme with baking soda...then harden off to "good rust" by
running motor approx. 1 hour.
Excellent instructions in post by Mainesail re rydlyme flush.
Changing internal engine zincs: check every year, my experience
have not had to change every year as boat lives on fairly isolated
Shutting down motor at end of day
have followed since new,
recommended by Yanmar/Mack Boring...idle motor short while to cool...then run at very hi RPM's immediately before shutting down.
By following above I am still with original mixing elbow,
check it every year or so with none/minor carbon buildup.
One last point, was told years ago and follow...don't baby motor
run her hard under load. Mid range RPM's with no load will wear
more than running at max. RPM (80-85% max. rpm's)
Am quite sure that I'll be long gone and this raw water motor
will still be in service if looked after and not babied!
Hope this helps,