That looks like mixed coolant, HOAT with Ethylene glycol, flush it soon.
Already beat you to it man, just not posted up yet. Not a chance in hell I was driving it round making cream cheese.
Strangely (or as I’m rather hoping) the coolant that was in was fine with the coolant that was put in to top it up - just rusty. They weren’t mixed types and were fine for a week and about 300 miles, then suddenly in one journey maximum cream cheese.
Tbh it looks a lot more edible than some of those American cheeses…
As a 'Murican, I can confirm
We’ll be having none of them advisories here:
Admittedly it’s original rear brake discs finally had to be changed but no matter, can’t really complain. Also done a few hundred miles now sans any cream cheese in the radiator, I am pleased to report.