I have an engine
guard on my primary engine
and it has paid for itself already going off well in advance of the engine overheating
by simply clamping the sensor probe after the mixing elbow
Something reduced water
flow - exhaust water
temp increased and alarm
Its not pretty, its surface mounted but it works.
Pretty simple device so that had me looking for a diy
ish alternative for the genset and something i could panel mount and I found this
AutoSpeed - $25 Temperature Controller and Display!
Bought it, a piezo buzzer and a longer probe to reach down a deck
level and wired it up as per directions but temp adjusted back to 47c.
Works a treat.