SIG I think so ur right ,
Radiator bottle was filled with derty water and a dirty thick layer like soil is filled upto (lower level ) - I have changed that water and put TIN GREEN Colant ,,,,,,,, But after that i am still suspecious about radiator performance , because the same dirty thick water layer is upto lower level of the bottle .... But no heating issue
Suggest me , wash the radiator with Radiator Washer or not