I've searched and it seems that the common causes could be water pump, egr valve or head gasket?
I've checked the following so far that I read of as possible causes:
1) Can't see any dirt/oil in the water tank.
2) No sludge on oil cap or dipstick (did oil change service a week ago and old oil was fine
3) No apparent steam coming from the exhaust.
4) No sweet smell of coolant in the cabin.
I haven't checked around the water pump or oil filter housing yet for leaks (my daughter's only home at weekends)
Can someone suggest a good way to properly diagnose the most likely culprit that I should tackle first
Thanks