Got to let some amount of water out first
Yea, I let the water out, I was considering using back the same water but found out the water was a little bit brownish. I think it's from the coke although I tried to make sure all the coke is out of the system lol. Should have use white vinegar, NSK selling them for cheap. Overall, I learnt quite alot from just flushing the cooling system of the car.
This discovery alone considered a plus already. Sudah untung
I also found that my old thermostat is still working , I'll just keep that as a spare and use a new one.