Brown rusty water from radiator

[saltshaker]

I’ve always used Detout Power Cool in mine. 190 is still too hot. Mine will run 178 all day long. WOT they stay the same.

 

[kingsley_oasis]

Is it possible you are getting cross contamination from raw water side. Though I would expect loss of coolant in that case.
A pressure test of the coolant system and also a check to see if exhaust gasses are getting in coolant may be necessary if condition does not clear after coolant replacement.