Shear Stresses Imposed on Oils During Low-Temperature Starting

The shear stresses acting upon engine oils during low-temperature starting are estimated and compared with the shear stresses of several engine oil pumpability tests. The area around the pickup tube and the flow within the pickup tube are considered. The shear stresses in the area surrounding the oil pickup tube are appreciably higher than the yield stress limit of ASTM Standard Test Method for Determination of Yield Stress and Apparent Viscosity of Engine Oils at Low Temperature, (D 4684), and much higher than the shear stress of ASTM Test Method for Low Temperature, Low Shear Rate, Viscosity/Temperature Dependence of Lubricating Oils Using a Temperature Scanning Technique (D 5133). In the flow of oil up the pickup tube, the shear stress is in the same neighborhood as the shear stress of ASTM D 4684.