I need to top up my engine oil and Audi have provided me with a 1 litre bottle of Castrol Magnatec Professional OE 5W-40 engine oil. I'm never 100% convinced with Audi dealers (past experience) so I checked on the Halfords and Castrol website where you can enter your car reg and it tells you what to get and low and behold it's slightly different - Castrol Edge 5W 30.
What's the difference? Am I still ok putting the stuff Audi supplied me when I purchased the car in? What does the 30 or 40 mean?