my radiator was leaking coolant from the joint between hose pipe and thermostat valve, @ skill rightly pointed out that i should seal that area.
when the mechanic opened the hose pipe, he also advise to change the radiator or get it fixed so the following were changed.
Radiator ( suzuki genuine) Rs 6500
Radiator hose pipe (Rs 300) suzuki genuine.
only thermostate valve seal was bad but since it looked rusted i also opted for its change too Rs 1500, suzuki genuine.
Radiator cap (Rs 500)
so the problem is now gone and works well with extreme teperature with water only, i didnt put coolant as i ve good experience with caltex coolant but i think its short so i will put caltex coolant only.