A COMPARISON OF THE EFFECTS OF CRANKING SPEED AND OIL VISCOSITY ON LOW-TEMPERATURE ENGINE STARTING

Recent cold-room studies have shown that the importance of engine oil viscosity is not in controlling engine cranking speed but in absorbing power from the starting engine. Cranking speed itself appears to be merely an index of engine oil viscosity. It is shown that engines may be successfully started at cranking speeds as low as six rpm if the viscosity of the engine oil is suitably low. On the other hand, if the viscosity of the engine oil is too great the engine may start but will not continue to run even at cranking speeds as high as 125 rpm.

These findings are important as they indicate that low-temperature starting cannot necessarily be improved by the simple expedient of increasing the starting system capacity. Rather, good low-temperature oil viscosity is required.