VARNISH AND SLUDGE STUDIES IN STOP-AND-GO TRAFFIC OPERATIONS 580251
The Engine Varnish and Sludge Group of the Coordinating Research Council has made an extensive study of the factors involved in the formation of varnish and sludge deposits encountered during low-temperature, stop-and-go driving. Twenty-four laboratories have conducted over 300 laboratory-engine tests.
Operating conditions which resulted in deposits similar in appearance to those encountered in the field consisted of cycling operations involving idling, low temperature-moderate load conditions, and higher temperature-moderate load conditions. This cyclic operation can separate lubricating oils, engines, and fuels in regard to their influence on the formation of varnish and sludge deposits. Vive different makes of engines separated a pair of oils in the same direction but at different deposit levels.
Comparison of results on several pairs of oils obtained in the laboratory cyclic operation, and in low-temperature, stop-and-go field service has shown a good degree of correlation between field and laboratory results with respect to cover sludge, no significant correlation with respect to piston-skirt varnish, and the field operation showed more variation between oils and higher level of oil-ring plugging.
A statistical analysis indicates the degree of repeatibility of test results that can be expected in a given laboratory and the degree of reproducibility of results that can be expected among laboratories. A new standardized CRC deposit-rating system has been developed which will undoubtedly improve reproducibility of results among laboratories.