After replacing the timing belt and tensioner pulley the engine started overheating?

My car initially was okay. Then I changed the timing belt and tensioner pulley, after some time it started to overheat on idle, if the car is running almost no problem, may be some time the temperature little up but on idle goes up more and more. I changed the radiator, water pump, thermostat and fan motor. No leakage and I replaced the coolant.
what could it be?