Vehicles without an oil filter generally require unalloyed engine oils. Exceptions prove the rule, of course.
Unalloyed oils do not contain any dirt-carrying (dispersion) additives, as the lack of an oil filter would otherwise cause permanent, increased wear due to dirt particles being kept in suspension. Instead, the oil allows the dirt particles to settle in the oil pan - so it is advisable to clean the oil pan every time the oil is changed.
Unalloyed oils are mainly used in pre-war vehicles - first and foremost, the manufacturer's recommendations of the time must be observed, although nowadays a slightly higher viscosity is advisable for purely seasonal operation.
If you do not have any manufacturer documentation or are unsure, we will be happy to advise you with our documentation and experience on vehicles dating back to 1900.
