Just had a new timing belt put in with water pump. Drove it home and the temp gauge flew up to red zone. Took it back they said air pocket in system. Bled the system. Drove home and same thing happened. Nothing changed. Temp gauge elevates past normal and into red zone when I idle or drive slow without air conditioning on. The weird thing if the air conditioning is on the gauge stays at normal longer.
What is the issue? Is it a bad water pump or thermostat? Or something else.