OF recent weeks public attention has bean drawn to oil dilution as a means of improving aircraft engine starting at low temperatures, and the following notes on the early history of oil dilution, details of a typical system and the effect of dilution on engine operation may be of some interest. The writer would, however, emphasise that he has no first hand experience of the difficulties which recently faced B.O.A.C., and these notes must therefore not be regarded in any way as related to that particular Airline's experience.