How do you maintain this system? As with the raw-water system, intake strainers, seacocks, plumbing, and raw-water pumps will need periodic attention. The closed side of the system may or may not have sacrificial zincs installed, and the raw-water side almost always will. Review your engine manual to find out where these are located, then check them periodically. Since it lives in a much friendlier environment, the thermostat on the closed system wont need the routine cleaning that one in the raw-water system requires. As long as the engine is operating at the normal, prescribed operating temperature, you can be certain that the thermostat is functioning properly.