[Werner]

Hello.


I am not sure if I have understood the core question correctly.

For vintage cars, a low viscosity can have the disadvantage that the shaft bearings leak leaking oil. Otherwise, a multi-grade oil is always better than a single range.

The most important is the API classification. Because of the non-ferrous metal compatibility. You should not go higher than "SC". Petrol engine oil API SC has anti-corrosion inhibitor, detergent cleaner, HD heavy duty additives. That is enough!

However, the oil still has to be changed many times (max. <1000 miles) because it runs without a filter and only then can the abrasion chips be taken out.