When the car is off and cold, the overflow reservoir shows a lower reading versus when the car is on and warmed up.
This is confusing because when the car is cold, it can be said that coolant needs replenishing as it is closer to the minimum mark, but after the car is warmed up, it can be said that it does not need replenishing, as it is closer to the maximum mark, so which one is right?
What state should the car be in when reading of the overflow reservoir, to make sure it is at the optimum level?