INCREASES in horsepower, compression pressure and engine speed, which have occurred in the last five years, have imposed additional duties on the lubrication system, points out the author, who declares that bearing failure is the most serious trouble resulting on the road from the use of oil temperatures exceeding 300 deg. fahr. To reduce this temperature to a figure between 210 and 230 deg. fahr., heat must be dissipated from the oil at a rate in excess of 250 B.t.u. per min. or a heat equivalent of approximately 6 hp.
Two types of oil-cooler, one using air and the other water as the cooling medium, are available at present. The former is extensively employed in connection with air-cooled engines, particularly on airplanes, but the latter is in more general use on automobiles. After listing the six requirements of a satisfactory oil-temperature control-unit, the author describes a number of tests made to determine the relative effectiveness of the two types of cooler as regards the dissipation of heat from the oil. Charts giving the results of the various tests supplement the text.
The discussion* brings out a number of interesting points, among which are the need for decreasing oil viscosity at low temperatures and increasing it at the higher values, the difficulty of predicting bearing temperatures due to the lack of fundamental data on lubrication, the progress made in dissipating heat by circulating oil, discrepancies in temperatures at various points in the oiling system and the reason for the differences in the heat-dissipating capacity of the three units described in the paper.