I agree that just draining and refilling is a bad idea; you want to flush accumulated dirt and sludge. Many service stations will not power flush anymore since there is a danger of causing leaks in today’s less than sturdy radiators. I used to drain and flush my own cars every 40,000 to 50,000 miles or very 4 years. A reverse flush kit in the heater hose works nicely with your garden hose. Unfortunately, for environmental reasons, you have to somehow capture the dirty fluids. For that reaon, I now have it professionally done, still every 50,000 miles. The long life coolant in new cars suggests 100,000 miles, but the coolant should be tested every year in the fall, and replaced if the anti-corrosion additives are used up. The irony is that many new radiators do n ot outlast the long life coolant!!