guys, currently have a problem with my car.
today, when my car was idle, the car temperature went up. the indicator indicate between the middle line and the upper white line, it just rise until there, i have to move the car, afraid that it will go up to the red line then the car temperature becomes normal again(normally below middle line when driving). what was the problem?

just now i just poured 500ml of water to my car till full.
17 year old saga btw