Aside from reducing the quantity of yellow grunge it didn't touch any of the brown stuff in the bottle. There's a marginally cleaner path from where the coolant makes its way from the radiator bleed through to the main chamber, but there are so many little chambers in the bottle with almost no flow it didn't touch it.
For the record, neither did :
- Sodium Carbonate based dish washer powder.
- 60% Nitric acid
- Concentrated Phosphoric Acid
- CLR.
After trying each of those, I probably spent the best part of an hour with a hose trying to thoroughly flush each chamber. I think that's where the restore was hiding because a vacuum fill thoroughly fills each chamber.
So, another hour or so with the hose flushing the rest of the cooling system, another blow dry and vacuum fill with DI water and another drive. A teeny little bit of foam on the top of the bottle, no taste, no colour and a pH bang on 7.4. I'm going to let it cool down, drop the DI water, blow dry it again and put the coolant in.
Next year I'll do another flush, but when I'm finished cleaning it out I'll treat it to a new bottle. I had already bought the Penrite Blue G30 (I tend to plan ahead and keep an eye on the sales), so I'll use that again and keep an eye on the colour this time.
I've not had a trace of dirt come out, so I think it's clean!. It'd bloody want to be.

