- Blue smoke is caused by engine lubricating oil burning
- The oil can enter the combustion chamber from several sources
- Worn valve guides, or seals
- Cylinder or piston ring wear
- Cylinder glaze
- Piston ring sticking
- Incorrect grade of oil – too thin and getting past rings, or valve guides
- Fuel dilution of the oil, making it too thin
- Blue smoke is often evident at cold start, which can reflect reduced oil control due to carbon fouling deposits around the piston rings and/ or cylinder glaze. Blue smoke should not be evident at any stage
- An engine may burn oil without the evidence of blue smoke, because good compression burns oil quite cleanly. However, it is not acceptable for any new engine or engine in good internal condition to burn large amounts of lubricating oil