I just clocked 1000 miles on the hemi in my 68 GTX. It's an all new engine built from one of the cummins made blocks with stage v heads. 'Been noticing it running a little warmer. It's never boiled or puked out the overflow but running to the right of normal. I had the original 26 in radiator recored with a 3 row high efficiency core, 160 thermostat (I didn't know about high flow t stats at the time.) and I used gold coolant. I work in a new car dealership and have always thought the gold beat the old green hands down. A recent article in mopar action agreed. Anyway looking through the fill neck about every flue I can see is clogged. Scratching with a pick confirmed it is rust. Was the gold coolant a mistake, or maybe because its a new virgin block? What's a good chemical that will clean it without making a mess? It's detailed nicely and I hate to ruin the paint on the engine or anywhere else. Is there something I can run and drain the block and radiator afterward that will dissolve it? Also if I can get it clean what coolant would you run and is there a good additive to keep it clean?