Hello Shazza. Thank you for reply. I will follow your suggestions. When I rinse radiator with hot water (and then with distilled), it looks clean, pellucid with no color, also no "garbage" in sight. Just when I fill it with mixture of vinegar and hot water (procedure is half an hour with lots of shaking) liquid coming out of radiator is blue. That was three loops so far. I was wondering why is that. And thanks for invitation . Greetings.