I just changed my thermostat and the housing has a very small leak almost invisible while the car is idle at the correct temperature. Once I run it and there is more pressure might it come loose or explode off? I assume it may be leaking because I didn’t clean the surfaces but I will buy some sealant and try that too
Use the permatex gasket maker for thermostats and water pumps. It will not explode but it will leak and get worse.