Let it warm up.Then shut off and feel the rad at top and bottom.It should be pretty close to the same temp.Try pulling the plugs that screw into the block.Use a 6 point 9/16s to remove them.Most wont even drain because of crud in the block.You have to use a screwdriver to open them.Flush it with the plugs out.SBs I fill the block thru the stat opening and then install the stat.Rocky