Certain other parts of the lubricant are thrown up against the hot surfaces, and reach temperatures at which they "crack." This results in carbon being deposited after the liberation of gas and lighter distillates. These also combine with the lubricant. This combined dilution makes the lubricant so low in viscosity that it is consumed at a greater rate than new oil and does not amply protect the surfaces. In consequence of this condition, it has become the custom to use very heavy lubricants for these small high-speed engines, oils that formerly would be selected only for the lubrication of the slowest speeds, highest temperatures and greatest weights in any mechanical machine. These oils place a heavy burden on the engine for the first hours of operation and until they become diluted with fuels, after which the viscosity is under no control whatever. The dirt and dust in the air entering the engine, mixes with the burned oil on top of the cylinders and in the combustion space and forms "carbon" and coke, which has to be removed at stated intervals. Some of this dirt also finds its way to the crankcase where it mixes with the lubri cating oil. When the lubricating oil is thin through dilution the abrasives add greatly to the wear of the surfaces.
Air-cleaners and oil-filters are being adopted to correct the dirt situation. Nothing of a permanent nature has so far been accomplished in preventing or removing the fuel dilution and, as a consequence, uncontrolled lubrication of over 25,000,000 automotive engines in the United States is being carried on with unusually heavy lubricating oils contaminated with from 5 to 45% of fuel in the winter and a somewhat less percentage in the summer.
The consumption of oil in the automotive engine is influenced by the engine speed and by the volatility of the oil. With a low priced 6 cylinder car, at 3o m. per hour, a gallon lasted 2,000 miles; at 5o m. per hour the consumption increased to a gallon in 46o m. for a "non-volatile oil" and 32o m. for one more vola tile. (Mougey, National Petroleum News, Nov. 9, 1927.) Con
sumption of oil in any automotive engine is also dependent upon the viscosity of the oil while operating in the engine. This is the result of the viscosity of the oil as manufactured, which is subject to control, plus the effect of the heat of the engine, the friction of the oil and plus the mixture of any lighter petroleum products that may dilute the oil. ("Liberty Aero Oil," Journal American Society of Naval Engineers, Feb. 192o.) Modern force-feed systems for the application of the lubri cants are very severe in their treatment of all lubricants that are not particularly Ldapted for the continuous lubrication of the machines to which these systems are attached. Lubricants can be so well made that they will undergo but slight change in such systems, while other lubricants will show the results of much wear. The officers attached to the U.S. naval experimental station at Annapolis, Md., have been making chemical, physical, practical and service tests of lubricants for many years. From the data so assembled a method has developed of grading the lubri cants on the basis of the changes that have taken place during use under actual operating conditions, or preferably under conditions which simulate operating conditions as to pressures and tem peratures but from which all chance for dilution and contamina tion is removed. In determining the acceptability of force-feed and motor oils a "work value" formula is used to secure com parisons between the viscosities, neutralization numbers, pre cipitation numbers and carbon residues on the same oil when new and after 1 oo hours endurance test. Lubricants that change the least are given the highest value. The lubricants are then graded as to value by applying the following formula: Service cost per gallon —Cost per gallon Average work val The lowest serv Average ice cost per gallon is considered the low bidder. ("Purchase on a Work Factor Basis," p. 697, Journal of American Society of Naval Engineers, Nov. 1928.) The methods developed are for the purpose of allowing purchases of lubricants and other ma terials upon a work factor basis instead of a price basis and the general adoption of this plan by the industries will stimulate the production and use of the finest lubricants for the most modern methods of application to present day machinery. (W. F. P.)