Necessity of the engine flush:

• Before upgrade to a superior oil specification (e.g. API SL replaced with API SN)
• Low quality (high sulfur) fuel used
• Previous drain intervals unknown or OEM recommended intervals exceeded
• Questionable quality of the oil used earlier
• Previous product data unavailable

Purpose of the oil flush:

• Removes accumulated sludge and deposits
• Removes drained oil residue, wear particles and by-products of the fuel combustion.