I did a radiator flush today. Drained fluid, filled with distilled water, drained 2 more times with distilled water. Then filled with 50/50 mix. I could only use 1 gallon of the mix because radiator was full. it is supposed to take 2. I was told that half of the fluid is in the engine block and to drain it one more time and fill it with fluid. The next time I fill it should i use straight coolant or use my second gallon of 50/50? if i do use the 50/50 will it be too diluted because of the water i put in before?