Engine is overheating.
Filling the overflow to the correct level will suffice as the radiator will draw out what it needs.
you add coolant to e150 thru the radiator overflow bottle
Open the radiator drain and let drain into a catch basin. Run water through the radiator by filling through the radiator cap with a hose till the water coming out is clear. Fill through the overflow bottle if there is not a radiator cap present.
the light is triggered by a switch inside the overflow bottle, If the coolant level is low when the engine is cold, it will trigger the switch to turn on the light until the cooant warms up and expands. The hot water expands and flows through the radiator cap and into the overflow bottle and shuts the light off. Then once the engine is shut off and cools down, the coolant will flow back into the engine again and empty the overflow bottle. so if the light is on, you need to fill the overflow bottle to the "cold" mark.
the water overflow tank
Most vehicles have a removable cap on the to of a valve cover to add oil. Coolant is added either into the radiator overflow bottle, of the radiator itself depending on how the system is designed to have it added.
The radiator is not meant to stay full all the time. When over full the excess will flow to the overflow bottle. If that is not your problem, it is possible you have a head gasket leak and you are burning it or it is going to the crank case and you will have milky oil. All of these are conditions which will require service by a mechanic.
too much water added the overflow is designed to let out water.onece the radiator reaches the required pressure,the excess water is exhausted thru the overflow
unplug line at bottom of overflow or bottom of radiator
The bottle will expand and overflow.
If your 1997 Subaru Legacy is the same as My RS-B Twin Turbo?, the Radiator and Overflow bottle have to come out and the Thermostat is at the front of the Engine, down the bottom-just to the right of centre, (Thermostat is inside the bottom radiator hose), - My Thermostat just twisted/pulled out, let all old coolant flush out-put New Thermostat in its place, Radiator and Overflow bottle were put back in and radiator topped up with fresh coolant and water, Overflow was filled to second line as it should be, car was started with heater on full for 5 minutes to disperse any air in water - (note) after adding fresh coolant, add water in Radiator till it can't take anymore-to show its filled properly.
If you are speaking of a radiator in an automobile, there is a plastic bottle on the side of the radiator, and it is marked for the fluid level; "ADD" or "FULL". The cap on the bottle will say "COOLANT ONLY" or words to that effect. Do not overfill. Older model vehicles you will add water to the radiator itself. Remove the radiator cap, slowly, and pour in the water. NEVER REMOVE THE RADIATOR CAP IF THE ENGINE HAS BEEN RUNNING! Wait until it cools down.