warning lights

Hello,

I'm having a 1.6i Octavia since 2000, and pretty satisfied. I have done some 105000 km and never had major problems. During our vacation I had an oil problem (orange light of oil level went on) so I checked it and added 0.5 ltr. I think this was due to the fact they forgot the extra oil while changing the oilfilter.

All seemed fixed and we drove on towards Italy. some 100 km further instantly the orange engine light went on. The manual tells me this means the epc has put down and a spare programm is doing the work. After some days the light went out, but after we returned it has frequently go on again. What could this mean? Yesterday I took a look and the black plastic box on the left side (cooling system) made a strange ticking noise. Could ther be a link?

Kind regards