Two comments.
[1] I know from experience that blocks that sit unused for years develop rust in the water jackets, sometimes like grains of rice. They will quickly block the rad tubes. There is no way of getting ALL of it out, no matter how many flushes/cleans you do.
This debris has probably blocked the rad, which will need rodding out. Here in Oz we can buy a filter that goes in the upper rad hose & stops it blocking the rad. It collects the debris, which can be removed. Gradually, over time, all of the debris will be removed by the filter & the filter can be removed, if desired.
[2] I would use a 180 stat. The 180 rating means it opens at 180 & may not be fully open for another 20-30*.
