When you flushed your system, you probably only flushed the cleaner out of the radiator. Whenever you use a flush in your car, you need to keep refilling the radiator with plain water, running the car, empting the radiator, repeatedly until you remove all of the flush cleaner. Alternatively, if you are skillful enough to empty the coolant out at the engine block (where there are usually bolt plugs you can remove there to empty coolant out of the engine block directly) then you can get the soap/cleaner out of there faster. Coolant in a car is held in much more than the radiator. The engine also holds lots of coolant. So when you put the cleaner in your car, it was sucked back into the engine and didn't stay in the radiator. When you flushed your system, you probably just dropped the fluid out of the radiator only. The cleaner in the engine was still there. That's my guess at what you are seeing right now. You need to use standard water and keep empyting the radiator, filling it with water, (following all your other procedures for making sure the thermostat opens, etc) running the car, and making sure the water makes its way through the system. Until I see pure water at least 3 or 4 times after driving and filling/refilling a system with water, I assume there is still cleaner in there.