Not sure why the surge tank would have a line indicating a working level.
It should always be full. When the engine heats it displaces the coolant to the overflow tank in the fascia. Upon engine cooling, it ***** the fluid back in. If you only have fluid to that red line, you have a huge air pocket in your cooling system, and if the system is working correctly, that air will be replaced by coolant from the overflow tank. The typical breakdown in this system is when either the cap on the surge tank is bad, the hose from the surge tank to the overflow tank leaks (usually at the hose ****** @ the surge tank cap), or the overflow tank is allowed to dry out, meaning upon engine cooling you will **** in air and not the displaced coolant. Of note about the overflow tank, it is vented, and there will be evaporation. How fast depends on how often you drive and what climate you live in, but the level will go down on it's own. Since the glycol component of the coolant does not evaporate (the water does), when you top off the overflow tank you only need to add water. This will eventually disperse itself into the system as the car is heat cycled. However, if you live in a climate where the car could be exposed to freezing temps, it would be better to add the standard coolant mixture when topping off the overflow tank.
You want a clamp on the line by the cap. It does not come that way.
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Fill the overflow tank from there.
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