So there must be some rust deposits present in the system by now..
REMOVE TSTAT VALVE BEFORE USING ANY SORT OF FLUSHING TECHNIQUE..
Previously de-rust the system using citric acid flush method..
Then neutralize the effect of acid by using baking soda.
After that check for leaks. If the system is heavily rusted then be prepared to fix the leaks which may pop out.
Use good coolant like Caltex, Toyota, Honda, ZIC... All are good..
Caltex, Toyota and Honda coolants are long life coolants so using these would be good atleast for 5 years use...
ZIC coolant works good for 2 years it comes pre-diluted..
If you don't want to spend much money then take guard coolant and use that for maximum of a year not more than that..
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