One would presume that after the first drain/refill that there would remain 2.5 liters of coolant in with the 8 liters of distilled water you filled it with, plus 2.5 liters of water already in from original fill (IF the original fill was still 50/50) . This would make it ~ a 19% mix of coolant (10.5 water, 2.5 coolant). Provided the mixture blended completely with the water, when you drained and added 8 liters of straight water, you drained out a touch under 6.5 liters of water and a touch over 1.5 liters of the original coolant. This leaves ~1 liter of original coolant still in the system. Refilling again brings the ratio down to .03%. So your remaining 5 liters is only .39 liters of coolant, the rest straight water. Topped off at 50/50 gives you 8.6 liters of water to only 4.39 liters of coolant (34% mixture).