What oil is best for older engines?

For older engines, It is best to use high-viscosity fully synthetic oils such as Shell Helix Ultra 5W-40 or Castrol Edge 5W-40. These oils contain additional anti-wear additives and detergents that can compensate for engine clearances caused by wear while minimizing sludge buildup. Due to prolonged use, older engines develop increased internal component clearances, where high-viscosity oils provide enhanced oil film protection. For instance, Castrol Edge reduces wear by 45%, while Shell Helix Ultra decreases sludge formation by 90%. Avoid low-viscosity oils (e.g., 0W-20) as their inadequate oil film strength may cause excessive wear in older engines. Always prioritize products meeting API SP/SN or ACEA A3/B4 specifications to ensure proper high-temperature shear stability. The oil change interval should be reduced to 5,000-7,000 km, complemented by periodic engine cleaning services to prolong service life.