won't start when getting hot

[costinstn]

I have a s80 2,9 from 2002,and lately i've been having some problems..first,the engine stoped suddenly a few months ago when i was driving it quiet strong on mountain roads..but it started again after 3 atempts...as the summer temperature got higher,the problem got more frequent.lately,i have to wait sometimes more than half an hour to get the engine to start..waiting for the engine to cool down,i poped up the hood,and after a while,i heard a clicking sound,and after that the engine started imediately.At long distance trips,it doesnt have any problems,just inside town and when the outside temperature goes over 85 degrees(around 30 celsius)
if anyone know what the problem might be,pls let me know...thanks