It is often said on the site that loose tolerance engines may benefit from a W50 oil and tight tolerance engines will do better with a W30. How do i know if my engine has tight or loose tolerances? The engine in question (a 1999 VW/Audi 1.8T) has used for most of its, 133,000 km, life Castrol Syntec 5W50 and has never needed make up oil. Not even a drop. Currently, the engine is 1000 miles in on an Auto-Rx rinse with Penzoil 5W30 and still has used no oil. Does this mean I have a tight engine?