As is use a radiator flush additive to clean the coolant system? Or a simple drain and refill? You can install a flush kit, which is nothing more than a plastic connection in a coolant hose connected somewhere between your water pump and your thermostat. This allows you to flush everything completely out of your engine by connecting a hose to it and flushing from your engine back through your radiator while the engine is cool. If you mean use a coolant flush additive, then simply follow the directions on the bottle to add it to your coolant. Then, after running the engine as prescribed on the directions, flush the coolant out as described in the instructions. You can do like I described above, or simply drain the coolant completely from the radiator (with the engine cool), then refilling with water. Then, with the radiator cap off, start the engine and let it warm up until the thermostat opens up (hot water will circulate through the radiator then). When this happens, let the engine run for a couple more minutes, then stop the engine, drain the radiator completely, refill, and repeat twice more. When you are done, drain the radiator again and add your antifreeze/water mixture and you're done.