either use good coolant like toyota company's recommended coolant (costs about 3-4k) and has a working life of 5 yrs, or consider that the coolant u used can further deteriorate u engine internals. Do seek expert opinion, i recommend Xulfiqar for the opinion .. if i remember correctly i think he already explained this in detail somewhere. The color of drained water shows rust content, which is just normal in any old car (though i don't know how old is ur car) using sub-standard coolant .. karachi has more rust related issues, so my recommendation would be a better coolant since the coolant also acts as anti-rust agent .. zic in my opnion is not a recommended brand for coolant
