The inside of the "rad" is the bucket stuff. The other two pics are the combustion chamber for heating. All I'm getting at is the inside of your rad from the cooling fluid probably needs flushed. Typically copper tube.Yoikes, that was a lot of crap! What was the rad installed in?!?!?
I wouldn't use vinegar on the nickle tho. If you try and flush everything internally it may not work well. If you pump in and out of a bucket the sediment will fall to the bottom of the bucket. All I do is keep the suction side off the bottom of the bucket so it doesn't suck the crap back through.