The best way is to hook up an electric fan,I have one on my 69 Bird.I have it hooked up with a proper temp.switch,so the fan comes on at about 215-225 and shuts off at 200-205.You can buy this switch at any parts store and make your own system,as for the fan I have a fan from a 1997 Crown Vic Police Cruiser,it covers the entire rad,I made some brackets from polished stainless steel and mounted it to the rad support where the shroud used to be.As for the clutch fan,it will turn slow when the engine is cold,as the engine warms up the oil inside the fan becomes thicker causing the fan to spin.If you want to find out if it is good,with the engine cool,grab a blade of the fan and try to move it back and forth,meaning towards the front and rear of the engine,if there is any amount of play chances are that the fan is no good.Hope this helps.