in every one of my engines ive built ive used 10/40 semi synth and sometimes 15/50 semi.
the thing that strikes me is that you dont here of many folks changing from the std semi to the fully synth.?
surely fully synth will be better regardless of how old the engine design is providing the engine is in tiptop condition to start with.
why would a semi synth of the same viscosity be better than a fully synth of the same viscosity?
isnt fully synth slightly thinner? if so,can one not select a higher viscosity rate?
oils always been abit