There are a lot of different oils available, the handbook for the Impreza states that 10W-40 should be used. My dealer uses semi-synthetic 15W-40 (I think Duckhams QX-R)and has said that you should just choose a good quality brand. Should I ask for fully synthetic in future and if he does not stick to 10W-40 then should I? I like the look of either Mobil 1 or Castrol RS fully synthetics.

 

Do a search for MOBIL we had a comprehensive reply from them last week? it was in general questions when you see you'll realise why I didn't just repeat it here.