THE bulk of low-temperature gasoline engine sludge is formed from the fuel rather than the lubricant, according to tests performed by the authors. Their tests indicate that most of this sludge is formed in the crankcase lubricant from oil-soluble, low molecular weight fuel oxidation products. They report that oil-soluble, sludge-forming intermediates have been isolated from used crankcase oils.
Reduction in low-temperature engine sludge deposits by commercial “detergent – inhibitor” additive combinations is seen to be due mainly to an inhibition mechanism rather than a “detergency – dispersion” mechanism, as previously assumed.
Ability of some synthetic lubricants containing oxygen to minimize sludge deposits appears, according to the authors, to result from their ability to dissolve a substantial proportion of the sludge component which normally acts as a precipitating agent for the total sludge.
A cyclic laboratory engine test is described which produces the same type and yield of sludge deposits as obtained under very severe field conditions; namely, stop-and-go light-duty delivery trucks.