Hold in recirc and up arrow and the display will change to 0c then use the + to dial up to 49c and it will then display the coolant temp. However if the temp sender is at fault which is usually the problem, then this trick will show the same temp as the temp guage as they get the feed from the same sender.
What are the symptoms?
If running permanently cold with bad starting and stalling then it will be the temp sender - easy DIY fix, but buy a replacement from dealer (£10), don't buy an ebay cheapy.
If the car runs OK but is cold on motorway, but reaches 90 when idling in the drive for 10mins then sounds like the thermostat is stuck open.
If it's overheating then its stuck closed