Safe Viscosity for a Motor-Car Engine Lubricant 380166
MR. SPARROW'S paper emphasizes the importance of the question: “What is the minimum safe viscosity for an engine oil?”
Although he does not attempt to solve the problem, he presents material “accumulated as a by-product of routine engine tests and development,” which, he says, indicates that rather low viscosities may be safe for bearings if and when we can be sure that the amount of lubricant which reaches the bearings will be adequate. He adds that it also indicates the extent to which safe lubrication of the cylinder bores depends upon the ability to produce and maintain smooth surfaces on pistons, piston-rings, and cylinder walls.
He illustrates how a low viscosity is effective in increasing cranking speed and in reducing friction -thereby producing a gain in horsepower and fuel economy. He also cites examples to show the extent to which low viscosity is detrimental as regards oil consumption, blowby, and the protection which the oil film affords to the rubbing surfaces.
Finally, Mr. Sparrow discusses in some detail the effect of changes in viscosity upon the lubrication of pistons, piston-rings, cylinder walls, and main and connecting-rod bearings.