200k or 500k, if an engine is healthy, not consuming oil, there is no need to go to a thicker oil. It is a myth. Someone misguided you and now the damage has been done.
Experts may now guide on remedies for this.
However, if this is the same mechanic that recommended the thicker oil, I would find a better mechanic and get a second opinion first. Don't rely on the mechanic only, check things out yourself as well.