i am buying a 540 2002 euro spec. Which is the best oil viscosity to use? I searched over some forums, some recommend 5w-30 and others 0w-40. Also few recommended the castrol 10w-40.
what do u guys think?
Something ACEA A3. If you're interested in long drain you should look specifically for LL-01. This means that the oil is thick-30 and up. No "energy conserving" thin 5W30s or 0W30s.
Depending on your climate, synthetic may or may not be required.
Pretty much every 15W40 and 5W40 will meet the need, so will a lot 10W40s. In 30 weights you have more limited options - BMW 5W30 and GC are on this list, as other products available in your area might be.