You can get a radiator flush. If it's cheap, get 2 bottles. It's worth the trouble so you can keep your coolant green in colour.

It's normally in the area where the coolant is.

I'd also get a bottle of CLR and swish it in around your radiator for 15 minutes (With it off the car after flushing the engine with radiator flush).

My 3 favourite metal treatment products:
1. Emertan (Tanin Phosphate rust converter)
2. Emerclean (Phosphoric Acid based metal cleaner)
3. CLR Great for cleaning nuts and bolts. More Internationally available.
4. Emerguard. A brown Rust treatment paint. Great for underbody and structural metal sections during a rebuild. The car will never rust again (If kept dry).

The Emertan, Emerclean and Emerguard can be got near Tempe, on the Corner of Canal Rd and Princes Hwy. About $100 for all 3, is enough for one Datto rebuild. Opposite from the pub. (Pub on many corners in AUS)

Chris