My GF's car is 5 years and almost 60,000 miles. The owner's manual indicates that a radiator flush must be performed at 60 months. Around here, the going rate for such a procedure is ~$80. I'd rather save that money. If I've changed my car's oil, how difficult would a radiator flush be? Online, I found a few different ways of going about it, but the simplest method consists of draining the radiator, filling it with the flush, topping it off with distilled water, letting the engine run with the heater at full blast for about 15 minutes, and then draining and refilling the radiator with equal parts antifreeze and water after the engine has cooled. Oh, and I have a couple bottles of SuperTech prediluted antifreeze (apparently manufactured by PEAK) that have been sitting in our garage for, I dunno, maybe 2 years? Is it safe to use this stuff? So... whaddya think?