Rust particles as long as they are suspended in the coolant solution is tolerable unless its sludge. It is when they deposit themselves on surfaces that problems begin to precipitate.
If to borrow a term from OTEP, "rodding", is not recommended for radiators of light vehicles.
I wouldn't be so quick with using muriatic acid, its normally used as a treatment for cleaning stains and oxidation but it will also dissolve metals given the right conditions.
But there are engine flushes that are more alkaline based that are safer to use, just make sure you rinse your loop before you refill it with coolants.





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