What is the correct level to fill the Coolant water,in this

[Jennysbest]

Some people say different coolant levels for the coolant to be topped up to in this tank (picture attached)

What is the actual safe level of where the coolant should be filled up to on this diagram?
(the min - max ranges it should be topped up within) ?

There is NO high/ low level on the outside of the tank.



What is the correct level of where the coolant fluid should be topped up to??

Thank you