The correct choice of oil is a guarantee of long life of the vehicle and save your time and money on its repair in the future. The main criterion in selecting lubricants is the recommendations of the equipment manufacturer, engine, gearbox, etc. These recommendations can be found in the manual instruction. There you will find the manufacturer tolerances or standards to be met by oil for your vehicle, such as API SM, ACEA A1 and BMW Longlife-04. Appropriate tolerances of manufacturers or standards are indicated on each unit of oil packaging.
If the manufacturer offers several products for your choice, remember that the viscosity is not a direct indicator of quality, but only one of the physical parameters of the oil (such as, for example, density or the flash point), but very important. The main criteria are performance, which can be judged from the manufacturer tolerances and standards, which correspond to each product.