Ok, That's Turbo petrol is it ? newer 2001/2/3 AUM & AUQ engines like 0w-30w or 0w - 40w fully synthetic. For diesel never go lower that 5w - XXw
Call up the last servicing agent / Garage / Dealer and ask them what they put in when the oil change was done last time. Then top up with that or the nearest equivalent.
When your next oil change is due. You may then be in a position to decide. OK 2000 build, 6 years now - hmmn depends on mileage and engine condition - probably 5w- 40w castrol fully synthetic, unless you have a very worn engine.
See my post 10 days ago or there abouts