The information on oil viscosity and specification should be in the owners manual - you may need to select the climate temperate range for the UK as the tables printed are often multi-market.

Don't worry about the semi-synth, etc - viscosity and ACEA grade are the important bits.

If you haven't got the owners manual or it doesn't give it then contact Mitsubishi directly - some dealers are slow to change bulk supply oil specifications and can't be relied on to use/recommend the correct grade - the majority are fine but since you never know who the dumb ones are, check with the manufacturer or importer in this case.

Castrol have also been known to recommend a different viscosity to the manufacturer!

I'm not casting aspersions of dealers or Castrol - just going from my own experience of Vauxhall, Subaru and Hyundai.

thanks for the replies... .

the castrol website for my wifes v40 volvo said 10/40 but the 5/30 for the Lancer..

glad I went to the main dealer though, as it turns out the car has an outstanding safety recall...

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will have to look into it further...have the service/owners book at home,,,