A mechanic put some kind of seal it...Silver goop into our brand new radiator because car keeps heating up even though we just replaced the thermostate and coolant sensor. Water pump seems to be working, we're not seeing smoke and steam, just hot arrow up to top of gage. We're afraid the silver goop may have hardened into chuncks which may be blocking the flow of the whole system. Any suggestions? How do we clear any blockage , and of air as well.No water in the oil. No smoke from tailpipe. Any tell-tell proof of blown gasket head?