The Standard Oil Development Company has developed a new test for evaluating the sludge handling ability of lubricants. Oil Sludging Test measures the sludge handling ability of lubricants in terms of the time required to reach 50% oil screen plugging in cyclic laboratory engine operation. The manner in which sludge builds up in this test is similar to the way it builds up in field engines. Results correlate very well with those obtained in low temperature, stop-and-go field service.
The test conditions were chosen after studying the conditions found to be conducive to sludge formation in the field. A six cylinder, overhead valve engine is modified by enlarging the piston ring gaps to increase blow-by. It is then run in 4 hour cycles. Each cycle includes 1-1/2 hours of idle with 115°F. oil temperature and 2 hours of loaded operation with 180°F. oil temperature. This is followed by a 1/2 hour shutdown under cold conditions. Periodic inspections of the oil screen are made as the test progresses and the per cent oil screen plugging is plotted against time. Lubricant sludging “Life” is the time required to reach 50% plugging. Comparisons between lubricants are made on the same fuel.
The reproducibility of the S.O.D. Oil Sludging Test is good. It is described here in the hope that it may prove useful to others working on the important problem of low temperature sludge formation in gasoline engines.