[Tannaton]

Look at it this way - with new Volvo engines the come filled with the same oil that is used throughout their life and it’s not changed until 18k. Hence I would suggest it is a matter of personal preference.

The issue with mineral oil is that it decomposes at high temperatures and leaves deposits which can block oilways. This was generally only an issue on turbocharged petrol engines though.

However I did once rebuild an engine in an Triumph Spitfire, which even after 4000 miles felt “tight”. I had been using Agip Sint2000 which was a fully synthetic oil, I put the cheapest mineral oil in that my local factor sold and after 500-1000 miles it felt much looser and mpg went up.

That however is very old tech, I would be reluctant to do that in a modern turbo diesel, but it may explain where the suggestion came from.