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This article defines the attributes of motor oil and contrasts how petroleum and synthetic oils differ. Once you have the data, will you switch?
Leonard Laub, esteemed 928 Journal Editor (shucks! - Ed.), and I shared a recent disagreement regarding the suitability of 5W-30 synthetic oil for a desert-based shark (even though my owners manual indicates it is OK). Leonard then chided me to share my ideas with the Club, so here we go. As an introduction, I am neither a petroleum engineer nor am I affiliated with an oil company. My background is Porsche fanaticism, electrical engineering, and sales and marketing. The information is provided for the enjoyment and, hopefully, the intellectual stimulation of my fellow 928 Owners Club members. It is my sincere hope that this article provides a catalyst for a continued dialog and the creation of a truly scientific treatise on this subject.
This article is based on information gleaned from the following Internet references:
Synthetic Oil: Rx for Long Engine Life, by Curt Scott
More Than You Ever Wanted to Know About Motor Oil, By Ed Hackett
Modern Synthetic Lubricants for Engine Oil Applications, By: Richard G. Golembiewski, P.E. RIS Technical Editor
I recommend reading these complete articles; URLs are provided at the close of this article.
Properties of Motor Oils
Let's first establish a vocabulary to facilitate a basic discussion of oils. The most important properties of a motor oil, often included in data sheets, are:
- Viscosity: the property of an oil to develop and maintain a certain amount of shearing stress dependent on flow, and then to offer continued resistance to flow. Thicker oils generally have a higher viscosity, and thinner oils a lower viscosity. This is the most important property for an engine. An oil with too low a viscosity can shear and lose film strength at high temperatures. An oil with too high a viscosity may not pump to the proper parts at low temperatures and the film may tear at high rpm.
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