Hi Scotty and friends.

I have a 2018 Mustang GT, manual. For the 2018+ model, Ford recommends a fuel efficient engine oil with the A5/B5 rating (at 5w-30 here in Australa), such as Castrol Magnatec which my dealer uses. I track my car every couple of months and I spoke to someone from Castrol who said that for track use, their Castrol 'Edge' is a better product, but it doesn't come in A5/B5, only A3/B4.

As I understand (and as explained to me by the Castrol rep), the A5/B5 grade translates to the oil being more fuel efficient, as it acts a little bit 'thinner' in comparison to its A3/B4 counterpart at a given viscocity rating. He basically said for track use, the Castrol Edge A3/B4 is superior to the Magnatec A5/B5. I know one should listed to the manufacturer's recommended specs, but in the case where I track my car and Castrol reakons the 'Edge' oil is better for that, do you think it would be ok to use the A3/B4 Castrol Edge in 5W-30? I'd want to use the product more suited to heavy loads/track use like Castrol Edge, if I can.

Many thanks