Overheat Hi Sir, my Toyota Corolla over heats after about 15km. I have replaced the thermostat, flushed the engine and radiator. I have added new coolant. And checked for leaks, all is ok. When my gauge rises to 3/4 what I do is switch heater to max and fan on max then the temperature declines to normal. Any suggestions. Thank you in advance.

With due apologize I do not know about the model year, engine code and other specs of your car. But check the following to solve the problem.
- Check Tire inflation.
- Check the clutch and pressure plate (if manual transmission).
- Check the accuracy of temperature sending gauge. (the fan should automatically start when the temperature gauge reads center position position on the combination meter.
- Check the radiator fan air flow, throw pressure and fan direction (should throw the air inside towards the engine).
- Check radiator cap and reservoir for air leaks. Perform cooling system pressure test.
- Check all the radiator hoses for firmness. Any scale or coolant color can reveal the leakage.
- Re torque all the cylinder head bolts a little more.
- Check color of engine oil. If the color is seen brown or excessive pressure is built inside the cooling system, due to the exhaust gases released into the cooling system, the cylinder head gasket is burnt. If so replace the gasket and surface grind the cylinder head with a surface grinding machine.