Don't !
The internal pressures on pistons and other areas of lubrication related to metal content mean that running an aero engine on auto oil is a no no.
You think that modern auto oils are very advanced - they are. The problem we have is we are running on 1940's technology and it needs an oil formulation that suits the engine and it's operation.
I sat on the fence for ages regarding oil and after owning 10 aeroplanes, I now run on Shell multigrade, however, if my useage drops to below 5 hours per month I would go back to good quality monoweight detergent oil - 80 in the winter, 100 in the summer. Multigrade has a tendency to run off quicker and if you are in a normal moist shed or hangar, you will suffer from condensation within the engine which is destructive.
Bottom line, change oil on an hour/date basis - without a filter - 15 hours/4 months, with a filter - 30 hours/4 months
