Coolant smell - outside car

Everynow and again I get a bit of a smell of hot coolant from under the bonnet of my XEDI.

Dont seem to be loosing any coolant and no visible signs of a leak. Looking back thru cars history, it had the waterpump replaced not so long ago - could it just be residual smell from a previous leak or do I need to investigete further.

Are there common places where leaks occur ??

All hoses and connections seem ok but there did seem to be a small amount of dried coolant arount top of expansion tank - to these caps need replacing every so often ?

thanks

Chris

the plastic expansion tanks start to crack after 50,000 miles ,common problem ,have a close look , they are very fine cracks. . .only cure is to replace it,easy job, if ya dunt it dosn't pressurise and so ya coolant can boil orft. . .