Overheating woes

[Hairyman]

Have you tried removing the radiator and flushing it out with a hose? I tried this many years ago with a Golf and it solved my cooling problems.

No, it is a good suggestion though.  I have a set of Go Westy coolant pipe repair inserts I want to fit, so I had always intended at some stage to replace the bigger rubber hoses at each end of the plastic pipes, in which case I might as well remove the radiator, replace the bottom thermostat housing, cooling tower, and a few other bits and bobs while I'm there.  Having an 18 month old makes finding any time to actually do it waaaay harder 

I was looking into flushing and the internet suggested https://www.youtube.com/watch?v=s--5ft5YiHg to me, which mentions using a flushing additive.  I didn't know they existed but according to Penrite they are alkaline salts that help break down sediments and rust but are harmless to "all metals, plastic and rubber".  I know the wasserboxer is comparatively touchy about what coolant goes in them so I wonder if anyone has any knowledge about how they interact with wasserboxers?  If an hour or so with the flushing additive is not a problem for the bimetallic nature of the case and headstuds then it seems like a good way of getting all the old gunk in the cooling system moving.