HOT WATER CYLINDER
RAW WATER SYSTEM
The Nav Station...
Yanmar Pleasure Boat Marine Engine Help
Overflow bottle: ( 'fresh water' cooled engines only )
You can see this Yanmar 4LHA-STP engine is already filled with Havoline ( Texaco / Caltex ) Extended Life Coolant. Notice that the engine is cold as the fluid level is near the bottom of the bottle. As the engine warms up the pressure will increase in the cooling system until the valve in the heat exchanger cap opens and releases the coolant into the overflow bottle. It will fill to half way or more, roughly where I have drawn the red line. When the engine is stopped and it cools down, the vacuum valve in the heat exchanger cap opens, the coolant is drawn back into the engine and the level in the bottle will drop again.