I am soon going to be changing the coolant on my 05 WRX. It will be the first time that I have attempted to do this myself and I have done a search of the forum and found some very helpful info which is great. The coolant hasnt been changed for 2yrs and the car has probably only done 10-15,000Ks max in that time. The car itself has only done 45,000Ks. I will be using genuine coolant and I have a 5ltr container.

I just have some questions about flushing the radiator/ engine etc.

1: Do I need to completely flush the whloe sytem, just the radiator, or is it not that important.
2: If I flush do I need to use a flushing agent or just run a hose from the tap or better still pour in distilled water instead of using tap water.
3: Do I have enough coolant if I do a complete flush??
4: Do I need to add a Subaru Conditioner to the coolant. I ask this because I have seen on some sites and on You Tube that some people recommend adding a condioner to to it. It was mainly American sites and videos so I am guessing it may be just something they have to do over there for whatever reason???

Thanks for any helpful comments in advance.