Vauxhall Meriva engine overheating

The issue is, that at any given time a service light comes on, which I found to be caused by the engine overheating. It has never reached the red marker yet, nor has it affected the performance of the car, however it has now happened near to a dozen of times and thus far I have not been capable of narrowing down what it may be causing. At first I figured it may be the revs, but it has happened whilst idling, driving round town in lower gears as well as going 70mph (or more...) on the motorway.
I have thought it may be the filter or oil however, both have been changed less than two months ago.
The issue is always temporary and it doesn't last longer than a couple of minutes before the engine shows to have cooled down back to 90°C and the service light turns off - then the car doesn't do this again for a while.