Why are you topping up the oil just before a service? The oil you put in will be taken out and thrown away.

Or have you let it fall dangerously low/

You need to look in the owners manual - as well as viscosity, eg 5W-30, it's even more important to use the correct ACEA category, eg ACEA-C3 as using the wrong ACEA grade is likely to wreck any DPF and/or Catalytic Converter fitted.

If you sort out the correct ACEA category, then synthetic, part-synthetic or mineral becomes irrelevant - but even fully synthetic of the wrong ACEA category will wreck things.

Edited by RT on 18/11/2013 at 14:34

0w-30 Castrol Edge is fine. Don't use 5w-30, a lot if garages use it because it's more common than 0w-30. The iCtdi is quite fussy about its oil.

Castrol Edge FST 0W-30 meets both ACEA-C2 and ACEA-C3 so good for many cars.

Brave man OP, i couldn't drive a vehicle with the oil level showing minimum further than the next place oil is sold, let alone consider a 100 mile drive.