SOME EXPERIENCES OF FUEL DILUTION OF LUBRICATING OILS IN SMALL DIESEL ENGINES.

Fuel dilution of lubricating oils in small diesel engines is normally attributed to fuel leaking past seals, pumping elements or feed pump diaphragms. Some authorities advise that dilution greater than 10 to 15 per cent is inadvisable; others advocate an oil change if the viscosity is more than an S. A. E. grade. Another possible cause of dilution depends on fuel properties, nozzle design and aspects of air-flow into a cylinder. The fuel introduced in this way plays some part in the combustion process and influences engine smoke levels. The dilution so caused is speed and temperature dependant. The paper describes tests to establish the basic characteristics, the mechanism at work and modifications to minimize this cause of oil dilution. Some tests are included to show that some fractions of fuel that is diluting lubricating oil can evaporate during engine operation; heavier fractions, however, are more likely to persist.