07 Grand Prix GXP 78,000 miles. I don't believe the cooling system has ever been taken care of.. I would like to have it throughly cleaned and add fresh coolent..What is the optimal way to do this.? Are there system cleaning products to add a few miles prior to draining ? Is there different ways to perform a flush ? I am interested to know what will best and most beneficial in my situation .. As it is there are no leaks and no fluid loss and the system is 100% operational. This is for maintenance reasons ..as its recommended in the operator manual.. Thank you .