The suzuki township monkeys are trying to rip you off.Check it from any decent mechanic who knows how to work on the car.Check it yourself if it needs changing or not--whether car is mixing the water with mobil oil ,check it through its dipstick.Don't get caught by the chipmunks working for suzuki.They know nothing.They know how to spoil you car.
As you stated
"to car over heat ho gai or heat ke needle half say oper chali gai man ney radiator ka cap khol kar dekha to pani ziada garam nai tha itna garam tha jitna normally hum hath dhony k liey"
Its pretty much normal when you will drive mehran on 120Km/h.The sensor could be faulty which can't be traced by the goofs working for suzuki.