Hi Pink,
I found this article online and am posting it here (I hope, but doubt, the tables come out):
Part 1:
More Than You Ever Wanted to Know About Motor Oil
by Ed Hackett
(updated as of July 11th, 1999)
Date: Fri, 9 Jul 99 21:22:04 -0700
From: Ed Hackett <
edh@dri.edu>
To: "H. Marc Lewis" <
marcl@micapeak.com>
My "oil" article at
http://www.micapeak.com/info/oiled.html is the latest version. I haven't had the time or desire to do any more with the article. It is as up to date as it's going to get. Regarding the age of the data -- you can now usually find current data on the oil company's Web pages.
Choosing the best motor oil is a topic that comes up frequently in discussions between motorheads, whether they are talking about motorcycles or cars. The following article is intended to help you make a choice based on more than the advertising hype.
Oil companies provide data on their oils most often referred to as "typical inspection data". This is an average of the actual physical and a few common chemical properties of their oils. This information is available to the public through their distributors or by writing or calling the company directly. I have compiled a list of the most popular, premium oils so that a ready comparison can be made. If your favorite oil is not on the list get the data from the distributor and use what I have as a data base.
This article is going to look at six of the most important properties of a motor oil readily availiable to the public: viscosity, viscosity index (VI), flash point, pour point, % sulfated ash, and % zinc.
Viscosity is a measure of the "flowability" of an oil. More specifically, it is the property of an oil to develop and maintain a certain amount of sheering 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 loose 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.
The weights given on oils are arbitrary numbers assigned by the S.A.E. (Society of Automotive Engineers). These numbers correspond to "real" viscosity, as measured by several accepted techniques. These measurements are taken at specific temperatures. Oils that fall into a certain range are designated 5, 10, 20, 30, 40, 50 by the S.A.E. The W means the oil meets specifications for viscosity at various low temperatures depending on weight, and is therefore suitable for Winter use. 5W is tested at -25C, 10W at -20C, 15W at -15C, and 20W at -10C.
The following chart shows the relationship of "real" viscosity to their S.A.E. assigned numbers. The relationship of gear oils to engine oils is also shown.
_______________________________________________________________
| |
| SAE Gear Viscosity Number |
| ________________________________________________________ |
| |75W |80W |85W| 90 | 140 | |
| |____|_____|___|______________|________________________| |
| |
| SAE Crank Case Viscosity Number |
| ____________________________ |
| |10| 20 | 30 | 40 | 50 | |
| |__|_____|____|_____|______| |
______________________________________________________________
2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42
viscosity cSt @ 100 degrees C