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I'd replace the expansion tank (coolant res) cap, it may not be releasing excess pressure. Use the lower pressure black cap instead of the green. fcpgroton.com has them or at greater expense your Volvo dealer. Some auto parts stores may stock the right cap. That hose leak needs attention, perhaps a good time to replace all hoses, belts, T-stat, waterpump, T-belt depending on how old they are and how many miles on them. Have you seen any indication of oil scum floating in the expansion tank? Excessive cooling system pressure can come from a blown head gasket and that often shows as engine oil (and bubbles when running) in the coolant tank. Do replace that cap right a way. Hope this helps.