I just got the service manual for the Yanmar 2QM20(H) and 3QM30(H) engines.
It looks like everything you need to know to take it completely apart and
put it back together as well as the operating and maintenance info. If
anyone would like me to look up something specific, let me know.

The section on cooling shows an optional bilge pump that piggy backs onto
the raw water pump. I've always liked the idea of an engine driven bilge
pump and it seems like this could also be a back up cooling pump with some
plumbing and valves.

It's not clear what keeps the impeller from burning up when the bilge is
pumped dry but one drawing seems to show a hole in the plate that goes
between the two pumps. I imagine water leaks through to lubricate the bilge
pump. This would require the pump to be above the waterline or the bilge
suction line to have a high loop.

Does anyone have experience with this option or know if it is still
available?

--

Roger Long