Originally Posted by Solitude
.... Salt water
corrodes metal quicker when the its warm which is why raw water cooled engines have a lower temp thermostat...
of metals in saltwater is a complex problem, with many factors involved including: temperature, salt
concentration, oxygen concentration, fluid velocity and more.
The prime reason for running Raw-Water cooled diesels at lower temperatures
(between 130 - 160 deg. F, usually 140F) than Fresh-Water cooled engines (between 160 - 190 deg. F, usually 185F) is that the precipitation of chlorides in seawater accelerates with elevated temperatures
(Ī 130 - 165 def. F). When the salts fall out of solution (crystalize) at about 145 deg. F, they clog (scale) the engine
galleries, typically at the hottest parts
of the engine, which ultimately leads to poor water circulation, and overheating
This not only accelerates corrosion, but also, in extreme cases, can actually block passages. For this reason, most raw-water-cooled diesels have a thermostat set at 145 F, at least 40 F cooler than a closed system. Running at this relatively lower temperature reduces an engineís thermal efficiency, so a Raw-Water system simply is unable to produce as much usable power as its Closed Fresh-Water system counterparts.
Periodically, you need to disconnect the inlet and outlet hoses, remove the Thermostat Housing, and clean scale from the passages. The tube that connects the outlet hose to the exhaust elbow
is another common point for salt
buildup. A third place to check for crystallization is the Anti-Siphon Valve (if installed), which is sometimes installed in-line on the hose between the exhaust elbow
and the thermostat housing. This valve prevents water from flowing back into the engine. If it gets clogged so that air canít vent into the system, itís useless.