Running thinner oil, is my reasoning skewed?

[2EHA]

Think he's talking about the 2015+ S550 Mustang (6th Gen), which was the first generation of Mustang with RH drive for export.

they got Motorcraft A5. it’s what europeans used to think was a fuel economy oil, only about 15 years too late.

 

[alcyon]

Only in the US 5W-30 is considered thick.

 

[OM605]

Only in the US 5W-30 is considered thick.

5W30 is considered thin here, xW20 almost unheard of...