On Sat, 10 Nov 2007 11:23:06 -0800, "Capt. JG"
wrote:

We will routinely replace raw water impellers in all overheating situation
in the future, as well as positively check the flow of raw water cooling
throughout the complete system: through-hull to mixing elbow.

Based on my experience with the small Yanmar in my genset, I'd
recommend being even more proactive than that. The impellers seem to
self destruct after about 200 hours so it's better to replace them on
a periodic basis before that happens. One nice feature on my genset
is a temperature sensor on the exhaust elbow. It trips as soon as
cooling water flow starts to slow down. Supposedly you can buy the
sensors at Home Depot for minimal $$$s and attach them with hose
clamps.