Effect of Unleaded Fuel and Exhaust Gas Recirculation on Sludge and Varnish Formation

Based on evaluations of sludge and varnish performance in a modified Sequence V-C procedure, it would appear that reduced lead levels in gasoline and the use of EGR hardware will place at least as great a demand on lubricants as is the case today. Analysis of sludge from representative tests indicated that the total amount of sludge formed from unleaded fuel was essentially the same as when leaded fuel was used. Hence, it does not seem likely that engine oil drain intervals of the future can be lengthened.