I used RUST 911. Drove the car for a day and drained it. The water had turned black. Refilled with more RUST 911 and drove it fro another day. This time the water was light gray. Repeat procedure for third day and it drained crystal clear. Looking into water jackets and radiator everything was clean as a whistle without a speck of rust anywhere. I refilled the system with Evans Waterless Coolant. No Water = No Rust. I buy both from Amazon.com