Ahhhhhh the old stop leak fix! I have repaired and replaced more regulators because of stop leak than Carter has liver pills. If the regulator has a brass tube approximately 3 inches long and designates a flow direction, it is a thermostat for the regulator. The kinked hose is not helping either. The stop leak will clog up the regulator thermostat. These units are designed to run with engine thermostat and would be really impressed if unit does not run hot without one. As mentioned above, flush system, clean coolant piping to regulator and fix the kink. If after these suggestions and unit still freezes, we will have to look into possible bad regulator but it running tells me it has to do with regulator coolant flow.