We try to use our 8 kW Onan genset at least 1x per month just to keep it working. We usually don't need that kind of power and use our little Honda 2 kW generator preferentially. Since we don’t use the Onan often, our “system” for start up isn’t as smooth as it should be. Today, we actually forgot to turn on the raw water (cooling water) until the genset had been running a few minutes and our handy-dandy little “raw water failure alarm” started screaming at us to do something about it.
Thank goodness for that little gizmo! It surely saved us the impeller and a melt-down of the (plastic/rubber) exhaust system. It caught the problem before the Onan's built in system for overheat would have shut off the generator. Quite early w/no overheat having taken place but rather just the wet exhaust pipe was getting warm enough to set the alarm going.
Here's the unit we have: http://www.borelmfg.com/products_alarm.htm
Ours is the "twin" one which has a sensor for the engine and one for the genset.