Xulfiqar quoted this in some other post, Cleaned 2 of my cars, one of my friends car, works like a charm, here you go:
its called - tartari. and dont pour it directly into you radiator, you need to mix it in hot water first in a bucket, remove T stat valve, drain the radiator and fill it with your prepared solution and start engine and keep it on fast idle for about 20 minutes,
open up heater too.
Drain the system after the time lapses. The solution max concentration is 10% - e.g. if your system holds 5000 ml you need to prepare the solution with 500 grams of acid in 5 litres of water.
Admire the stinky, mud coloured water that comes out - dont drain it to the ground where you have grass or you will have a brown patch, this acid will kill the grass.
CAUTION: if your system is heavily rusted and packed with sludge - be prepared to repair leaks that may pop out.
Use a blower to blow out all trapped water in the block if your engine block drain is hard to get to or does not have it. Neutralize with some meetha soda(5% also aka baking soda) and flush out - it will take about half hour flushing to clean out the system - once done install T stat and fill up with coolant/water mixture.