"1) It's not unusual f
"1) It's not unusual for the temperature to go up after turning off the engine. When the pumps stop pumping, there is no longer any heat being removed. Even though there isn't any heat being generated, there is still a significant amount of heat in the materials of the engine, the block being the biggest source. It takes a while for everything to cool off without any coolant flow.
2) With regard to the temperature spike of 180-190, this could be indicative of the raw water impeller going bad. If you can't remember the last time it's been replaced, it's overdue. Not a hard thing to fix. A repalcement kit will run you $50. Another possibility is the thermostat starting to wear out an not fully opening, also a fairly cheap and easy fix.
3) If it's a raw water cooled engine, the coolant is the water the boat is sitting in... no need to add more.
If it's fresh water cooled, there should be a small plastic tank somewhere in the engine compartment with a tube going to the top of the heat exchanger (the cylindrical shaped thing, about 6-8" in diameter with a radiater cap on top of it.) The plastic tank is where you would add more coolant. There should be marks on it to indicate the right level for when the engine is cold and when the engine is at normal operating temperature.
4) It doesn't sound like you overheated anything.
The actual temperature to consider the engine "overheated" varies and has more to do with the actual temperature of the engine components than the temperature of the coolant, which is what you're looking at on your dashboard.
The formation of steam is the mechanism by which the engine will become damaged by excessive temperatures. Steam has practically no heat capacity and therfore removes almost no heat from the water jacket, which leads to a failure of some sort when lubrication breakdown starts to occur at localized hot spots on the cylinder walls.
Open (raw water) cooling systems are not pressurized and have a lower thermostat setting (160F) to limit boiling in the water jacket.
Closed (fresh water) cooling systems are pressurized and are allowed to run at a higher, more efficient temperature. The pressure in the cooling system surpresses the boiling in the water jacket, so they have a thermostat setting of 180F."
