Getting the correct grade of oil nowadays is so complicated there are so many different types. I like to do an interim oil and filter change myself in between services. According to the Kia list of recommended oil grades my 2017 1.7crdi should have 5w30 c2/c3. Does that mean either C2 or C3. I usually use Castrol Magnatec 5w30 c3 stop start but putting the vehicle details into Halfords website it says 'not suitable'.