Performance & Hotrod Business May '14

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May 2014 n Performance & Hotrod Business n 81 From A To Z Today's oil specs are identified by the American Petroleum Institute and meet the engine protection and fuel economy requirements of the International Lubricant Standardization and Approval Committee (ILSAC). Looking closely at the specs over the years will give a better understanding as to why oils keep changing. The earliest API spec oil was marked "SA." The "S" signifies a service/sparked ignition ("C" is used for diesels indicat- ing a commercial/compression ignition). The "A" was the first oil spec designation. Each progression from "A" to today's "N" was the result in changing needs for dif- ferent or improved oil. "SA" oils were designated for engines be- fore 1930. They were straight weight (single viscosity) oils that had no additives. Engines with these oils depended on a film of oil between the parts at all times, limiting the speed and pressure of the adjoining parts. Engine bearings were made from a poured material invented in 1839 by Isaac Babbitt using combinations of lead, tin, and zinc. Low compression and low speeds, etc., were necessary to prevent bearing failure and the average rod and main bearing life was less than 1,000 miles, because the lead and tin were expendable. The next oil spec, introduced about 1930 was "SB", containing additives including zinc dithiophosphate (ZDP) or zinc dial- kyldithiosphate (ZDDP), each commonly called just "zinc". This additive formed a protective barrier film that was (and still is) used to eliminate the wear of metal against metal. If you do not understand a need for this barrier, let your brake pads or shoes wear out and you will see that metals when rubbed together will gall and weld them- selves together. Multi-Weight Oils At the same time, multi-weight oils were developed. Actually, the common term "weight" is incorrect. If it were truly an indication of weight, 50-weight oil would weigh five times as much as 10 weight. So, exactly what do the numbers mean? Let's use 10W30 as an example. The first number, followed by the "W" indicates the flow rate when cold. The "W" means winter. The cold test is not the same as the high-temperature test so the two numbers are not related. The cold test has two parts. First the flow rate at a given cold temperature is mea- sured. A10W oil will flow at 0 degrees cen- tigrade. For comparison, a 0W will flow at -35 degrees centigrade. PHBMAYp58-91.indd 81 4/2/14 2:06 PM

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