Overheating

I have a 85 mk1 mr2 and it overheats I was looking at other mk1's and saw that they had something hooked up to the radiator liquid filler in the back right of the car (right of the intake manifold) and is that a component that might cause it to overheat or the defctive side fan on the right of the car.If any one knows the answers to my questions or might know a nother reason it overheats please get back to me.

When was the last time the cooling system was flushed? Is the cooling system partially obstructed or clogged? Is the coolant level correct? Are the fins in the radiator clean, free from obstructions? Does the fan work? Does the fan come on when it should? It the thermostat sticking? How old are the hoses? Are the hoses colapsing causing a restricted flow?