Hello,
1) Check head gas kit (symptoms of heated gas kit bubbles will form in radiator's water when you open the radiator cap and start the engine)
2) Check if water is not pupped from the bottle to the radiator
3) If it's an old model Mehran and you have installed euro 2 condenser it will cause an issue (this happened with me)
I had the same issue it's resolve by these 3 steps
