overheat

What is your question?

when i started it,overheat 20-30 min. 1.5 year, timing belt(radiator,water pupm,thermostat.) The mech.change thermostat,no good. Change the theperture countor sensor,no good. Water pump, no leak.The mech. said is the water pump.Took the car away. -------------------------------- when started and give gas, the temperure drops.when inde it overheat. The second mech. said is thermostat,new toyota make. Please advice.