C is for "commercial," and 
 S is for "service [station]."

 The letter "S" followed by another letter 
 (for example, SJ) refers to oil suitable 
 for gasoline engines. The letter "C" followed 
 by another letter and/or number (for example, 
 CH-4) refers to oil suitable for diesel 
 engines. These letters officially stand for 
 "Service" and "Commercial." 

 http://www.api.org/programs_services/quality/enginoil.htm

 http://www.api.org/programs_services/quality/oilchart.htm

 http://www.offroad-net.com/RoverWeb/OilFAQ.html

At 02:39 PM 5/29/99 EDT, Youngjs@aol.com wrote: >The C is for compression ignition - Diesel >The S is for spark ignition. > >Possibly there is an SAE engineer on the list with more info! We have been through that one recently. I had always believed the same thing, until the discussion on this list pointed me to the API page, where it was clearly laid out. C is for "commercial," and S is for "service [station]." The primary differences is the level of testing and documentation required meet those certifications; C being much more extensively tested and documented than S. The following words come from the API page: The letter "S" followed by another letter (for example, SJ) refers to oil suitable for gasoline engines. The letter "C" followed by another letter and/or number (for example, CH-4) refers to oil suitable for diesel engines. These letters officially stand for "Service" and "Commercial." Reference: http://www.api.org/programs_services/quality/enginoil.htm For more information on their different rating levels, see: http://www.api.org/programs_services/quality/oilchart.htm BTW, I found another really neat site that tells quite a lot of basic stuff about oil: http://www.offroad-net.com/RoverWeb/OilFAQ.html At 02:23 PM 5/29/99 -0400, "Glen & Karen" <karenandglen@erols.com> wrote: >>All the Commercial ("C") oil that I would normally use meets or exceeds the >>requirements of the Service Station grade ("S"). >> > > >Is that ok? Can the exceeding factor be a problem? In other words, can >there be too much of a good thing in the "C" oil when used in a small gas >engine? Not to worry. Since the primary difference is in the level of documentation and testing required to claim those ratings, the oil itself does not know the difference between one and the other. As it says on one of the API pages that I referenced above, the same oil may have many different ratings. If they meet the level of testing and documentation required to claim the Commercial ratings, then it is almost automatic that they will also meet the Service ratings. As an example, I have in front of me a quart container of Valvoline 10W30 oil. On the back, it says that it meets API Services SH/CD. Those are obsolete specifications, but they make my point. (This container has sat on my shelf for many years, being used mainly to lubricate whet stones for sharpening various wood cutting tools.) +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ :: Paul and Cindy Kruse :: KJV Joh 14:27 Peace I leave with you, 165 South Kenneth Court :: my peace I give unto you: Merritt Island, FL 32952 :: not as the world giveth, give I unto you. E-mail: plkruse@iu.net :: Let not your heart be troubled, 407-453-6206 :: neither let it be afraid. :: +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++