So how much it matters is down to how prestigous the car is?
What about an Aston Martin? Does it matter more then? Or a Noble?
I think how much it matters depends on the recommendations of the people who designed an engine. Todays 'old Ford engine' was yesterdays 'cutting edge' engine, it doesn't wake up one day and think 'I'm 10 years old, actually mineral oil is fine'.
What about an Aston Martin? Does it matter more then? Or a Noble?
I think how much it matters depends on the recommendations of the people who designed an engine. Todays 'old Ford engine' was yesterdays 'cutting edge' engine, it doesn't wake up one day and think 'I'm 10 years old, actually mineral oil is fine'.


The old is not really a factor - it's still a modern engine. And you're right, of course oil choice and following manufacturers recommendations is important. But I bet you 50p the ST200 owners manual doesn't say 'do not use Halfords own brand oil'. This mix proposed in the OP, if they are the same type and grade of oil is a total non-issue.