What oil to avoid?

When selecting engine oil, avoid using low-quality products or oils with incorrect viscosity grades that do not comply with the vehicle manufacturer's recommended standards. This particularly applies to oils with API ratings below the manual's requirements (such as using below SL-grade oil for older vehicles or non-SP-grade oil for turbocharged cars), as well as SAE viscosity grades unsuitable for climatic conditions (for instance, using 0W-series oil with excessive low-temperature fluidity in tropical regions or 5W-20 oil with inadequate high-temperature viscosity in cold climates). Special attention must be given to China VI-compliant vehicles, which require low-ash SP-grade or ACEA C-series oils to prevent particulate filter clogging from high ash content. Additionally, diesel and petrol engine oils must not be mixed unless explicitly labeled as universal (e.g., SP/CF). For example, 5W-30 viscosity suits most modern petrol engines, whereas high-mileage vehicles may need 5W-40 for enhanced sealing.