I'll be sharing how I flushed our Toyota Innova's cooling system without removing the thermostat. It is pretty easy but consumes a bit of time. So flushing is done when coolant is heavily contaminated or the system is dirty or whenever you'll switch to a coolant with a different color or brand. Changing your coolant in correct intervals prevents buildup or corrosion in your cooling system. So be always sure to check them and replace when needed!