1. When engine is cold remove radiator cap. Fill with coolant or water so you can see the liquid in the radiator. Start engine and observe, if you see bubbles after a short while, chances are you have a blown h-gasket.   2. When engine is cold remove radiator cap. put some food coloring in the radiator. Use coloring that is opposite color of your coolant. Place a white cloth over the tail pipe and hold it with a rubber band, Run the engine for about 15 minutes being careful not to blow the white rag off. Remove the rag and observe, if there is coloring on the rag, you probably have a blown h/gasket.