I have never seen any evidence that flushing the cooling system after repairs is detrimental nor that doing so beforehand is beneficial in any way. I am sure that the "I post a lot club" will flame me for this but it is what it is. If you have ever observed that the chemical flush with the VC-9 cleaner absolutely dissolves the lining in the system you would know. Of course, proper flushing and rinsing requires using a hose to back flush the system. Doing so will remove the contamination. People make out to be that there's inches of rust scale and dirt that it cant help but get trapped in the cooler... After that is complete most people prefer to fill and drain the system with distilled water. In any event - not worth losing sleep over. If you took care of your coolant maintenance, there really isn't much in the system to remove in the first place. People who get unsatisfactory results likely failed to run the engine with the cleaner in it at ~1,200 RPM for a minimum of 1 hour with the thermostat removed to allow the cleaner to be fully effective and or failed to flush out all of the iron cleaner which will quickly damage the corrosion inhibitors in the fresh coolant resulting in a repeat failure and usually in less time than the original failure took to occur. From what I have read in public forums, most advice will have you effectively flushing the system out if followed.
