What kind of oil is used for maintenance? The engine does not dig coal.

There must be a lot of sludge in the garbage engine oil, so I use German GT engine oil for maintenance now, which is grade 4 PAO engine oil, and it doesn't produce much sludge. The power output of the engine is obviously much better than before, and four or five pots have been used. I went to the garage to check the engine, and there was no coal digging again.