vfm@ihu1h.UUCP (Vern Metzger) (10/09/84)
[1] Additives: Popular Science, April 1976 "Synthetics are `inherently' more stable, so they don't evaporate or oxidize as easily as mineral oil. They have a `naturally' better viscosity index. They flow freely at low temperatures, yet don't thin out as much as mineral oils at high temperatures. Most have multiple viscosity characteristics `without' VI improvers. Finally, they have an excellent `natural' detergency and dispersancy." "What happens to the acidic wastes? Petroleum oils breakdown and you get resins and insolubles, we've said for years that it's necessary to drain oil periodically to get rid of the fuel- combustion garbage. But what we've been surprised to find is that it may not be so much the garbage as the degradation products of the oil itself. And with these synthetics oils, there isn't much degradation." (This last paragraph quote was by Leo Manley, at that time, Mobils's manager of lubricants and additives) Service Station Management, May 1980 "Refining crude oil is far cheaper than chemically engineering a synthetic base stock. But refining also compromises the lub characteristics of the base oil. Crude oil, as it comes from the ground, is a soup of thousands of different "fractions." Depending on the grade and whether it is a light or heavy crude, it might contain everything from asphalt and waxes to light and heavy oils to very light distillates that go into making gasoline. It also contains sulfur and other impurities. The refining process separates these different fractions, including those which are capable of forming a base stock for engine lubrication. The trouble is the refining process is an approximation so the base stock will still contain a variety of substances, including some impurities. There will be some fractions in the oil that thicken at low temperatures and others that will boil off at high temperatures over a period of time. There will also be some that tend to oxidize and form sludge deposits. To counteract such things the oil companies blend in various additives to improve viscosity, oxidation and wear resistance and so on. and this is where synthetics come out on top. Since the man-made esters and hydrocarbons that make up synthetic oil are extremely pure, the oil is free from the substances that can cause thickening at cold temperatures, thinning at high temperatures, sludge formation, etc. In other words, it's what "isn't" in it that makes it better. This means fewer additives are necessary, which in turn means the oil will last longer and perform better than its conventional cousin. Breakdown of the additives is the primary reason why oil must be changed periodically. As the additives wear out, the oil begins to thicken. It also loses its resistance to oxidation, sludge formation, etc. Synthetics, however, are far less dependent on the additives-the result being synthetics last much longer. To illustrate the staying power of the man-made lube over Mother Nature's blend, a standard SAE test compared the oxidation resistance of premium quality mineral-based oil with that of a diester-based synthetic. To pass the test, an oil must withstand 64 hours of sustained highway speed operation inside an engine. After 40 hours, the oil can be no more than four times as thick as it was at the beginning of the test. After 40 hours of such punishment, the conventional oil was 121% thicker. This compared to only 15% for the synthetic. And at the end of the 64 hours, the conventional oil was 186% thicker compared to only 18% for the synthetic." To summarize all the articles I have read, a general indicator that the condition of the oil (and the additives) would be its measured viscosity index. The chances that a synthetic with 25,000 or more miles on it and being within 20% of its original specified weight are much, much greater than a conventional mineral oil with less than 7,500 miles. A specification table contained in Pickup Van & 4WD, Dec., 1979, displayed data and test results of 23 conventional and synthetic oils, when subjected to the 40 hour test previously mentioned, the viscosity change of the synthetics ranged from 0% (AMSOIL) to 30% (Love Co.), conventional 5% (Shell) to <400% (Mobil Super). Most of the synthetics were under 6% and most of the conventional were over 55%. [2] Auto manufacturer support: Granted, car manufacturers don't support the long change interval claimed by the synthetic oil manufacturers, but they also don't say it's not possible. There are many reasons for this, for the consumer/buyer it means a significant increase in cost of an oil change, availability, possibilities of confusing a special additive oil (ex: ARCO graphite) with a true synthetic and also employing better filtration which I have mentioned in a previous article. My personal feeling are that they will get there, its just a matter of time. It wasn't too many years ago that the recommended interval was <3K miles now most are 7.5K or greater. In response to "fluke!inc" and his mention of a Service Manager for Toyota stating that using a synthetic during the warranty period would void same. Can anyone out there confirm this? If the buyers documentation (owners manual) doesn't contain such a statement it more than likely was made up by an uneducated bolt-busters. I have read many articles about the use of synthetics and have never come across documentation about a engine failure solely attributed to the use of a synthetic lube that meet the required specs. There is much confusion about a lubricants viscosity and the Viscosity Index Number. "The viscosity index number is a measure of viscosity change with temperature and the higher the index number the less the viscosity change. Motor oils which are used a a wide variety of temperature conditions should have a high viscosity index number. (It should be noted that the viscosity index number is not related to the actual viscosity of the oil or the SAE number. It is a measure solely of the "rate" of viscosity change with temperature.)" Quoted from the API's Motor Oil Guide. BTW, Mobil-1 and ARCO are 5w-30 and AMSOIL has 10w40 or 20w50 and some straight-weights. [4] Meeting specs: In regards to the SAE specifications SA thru SF and CA thru CD, I don't know of any automobile manufacturer that requires a combination of both "S?" and "C?" for a particular engine. The "S" specification is for "spark" ignition engines and the "C" is for "compression" ignition (as in diesel) engines. The letter following the "S" or "C" is the rating of that product, and the higher the letter the better the product. The current specs are SF and CD and they exceed the requirements of all preceding ones in their same class. The "W" (for winter) after the SAE number indicates an oil suitable for use in colder temperatures and the viscosity of these "W" oils must have the proper value when measured at zero degrees F. Those SAE classifications which do not include the "W" are suitable at higher temperatures such as are in the summer months. The viscosity of these oils must have the proper value when measured at 210 degrees F. Vern Metzger