There is no sure way to detect the H,G failing ,as rule of thumb 6 fails , compression to water [yes this will make your hoses rock hard and could have steam from tail pipe] compression to oil [milky foam in oil] water to outside engine [over heating can see the leak out of side of engine] water to oil [very milky oil]oil to water [rare] oil in water, but you can have 2,3,4 5and6 in combinations, but if you've got the bottle to do it ,tighten your H G bolts in the correct combination by another half turn , can save you a lot of grief [or snap ya bolts] its your call. . .