[Werner]

That depends on the amount of acid introduced. Short drive distances are very bad, long distances with oil temperatures >100 ° C are always good. An exact guideline can not be given for an A-engine, because these old engines have a bad combustion with many incompletely burned fuel residues. (Ethanol residue is bad!)

In large engines, oil samples are taken and the TBN is measured. A reading below TBN 2 (origin 5.5, for example) indicates that the corrosion protection has been used up.

In a classic car engine with oil filter, I would recommend an annual change interval. Our A engine due to the dirt removal max. 1000 ml. No matter which oil is filled in.