I am a fan of synthetic oils for modern engines with roller rockers etc and built to close tolerances. I am not a fan of synthetic oils for larger tolerance flat tappet engines where it has been shown that synthetic oils do not, as a rule, promote the rotation of lifters and pushrods as effectively as do good quality mineral oils for the simple reason that synthetics are a tad too slippery!
I know there are others with passionate views to the contrary who claim significant success with top brand named synthetics in their flat tappet engines... good luck to them.
The worst case I saw was the effect of a high cost synthetic in a Lycoming 6 cyl in a C-182 with less than 800 hrs of engine time since the previous rebuild and which required major work. A $$$ partial rebuild later and another 1000 hrs this time on a good quality mineral oil and the wear was minimal. In both cases the oil was changed regularly.
The Magnatec 15W-40W oil for diesel engines is probably as good as any.
MY99 RR P38 HSE 4.6 (Thor) gone (to Tasmania)
2020 Subaru Impreza S ('SWMBO's Express' )
2023 Ineos Grenadier Trialmaster (diesel)
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