This paper covers a number of recent engine oil developments, with particular emphasis on the use of new ashless-type additives. Additives studied include ashless dispersants, an ashless antioxidant, an ashless antirust additive, an organo-tin compound, and ethylene dibromide. In general, combinations of these additives can provide improved lubricating oils.
In oils for high-output outboard engines, it was found that ethylene dibromide is extremely effective in prolonging spark plug life, regardless of the type of detergent or dispersant used. In combination with an ashless dispersant, it also reduced preignition tendencies. In addition, the use of the organo-tin compound in outboard oil has shown a striking antiwear effect, allowing a several-fold increase in gasoline-to-oil ratio.
Ashless-type additives are also finding use in motor oils. Some ashless dispersants have shown exceptional ability to handle low-temperature varnish and sludge deposits. Oils containing these ashless additives require supplemental antirust protection. Results are shown on several oils treated with an experimental ashless antirust additive.
The new additive-type aviation oils for piston engines are brieflly discussed. In a recently developed high-temperature, single-cylinder engine test used to qualify these aviation oils, a unique ashless antioxidant was shown to be particularly effective in minimizing piston deposits, ring sticking, and ring wear. This additive has also proved effective in various types of oils used for a variety of other applications.