I recently replaced the head gasket in my Renault K9K (700) 1.5 DCi, due to a cylinder/cooling system type failure. As such, the cooling system is full of partially burned diesel. Despite having flushed the cooling system every few days for a couple of weeks and having used commercial coolant flushing products a couple of times, the coolant continues to turn black after relatively little use.
Has anybody got any tips or tricks on flushing a stubbornly contaminated cooling system? I've read of people having success with using a pre-dissolved low suds washing powder, is that a sensible idea? Do I just need to be more patient?