Product Review: Thermo-Cure cooling system flush.

You might check the MSDS sheet to see if it lists the secret sauce. It seems the Prestone flushes today are much wimpier than in the past. I bought 10 lb of citric acid on ebay and use 1 lb in the radiator with tap water (after flushing), run for about a week, then flush many times to remove all acid. I think that is what the older Prestone flush used. People swear by many acidic products like lemon juice (above) and even Coke (supposedly ph of 3). To derust small parts, I leave in a jar of EvapoRust, but too pricey for a car's cooling system. I also use Phosphoric Acid (Concrete Etch at Home Depot), sometimes after EvapoRust to remove more or at least convert it to black oxide in pits. Most derust sprays have that. But, I think risky to use on aluminum (timing cover in small-blocks, water pump in slants, ...).

Worst clogging I've had is in my 1996 Plymouth Voyager. I recall using "extended-life coolant" at one time, before the horrors of Dex-Cool was known (and not marked thus on jug). I started getting dark corky-like stuff floating at the top of the radiator, which might have been reactions with remnants of green coolant. After flushing and refilling with green, I later got a lot of rust (left streaks on my concrete driveway when flushed), so maybe some fight between acids still ongoing. I finally got a new radiator and flushed the block alone and brown crud was still coming out. Installed a screen in the top hose to try to catch remainders to not clog the new radiator. All my other vehicles I've changed to Evans Waterless Coolant, so no such concerns. The various coolants with varying chemistries and funky colors today will spin your head.