| After reading a couple questions regarding which type of oil to use and knowing that oil technology has changed with the EPA's stricter guidelines, I have decided to post an update such that people, at least here, will have better knowledge of today's oils. For some, this information may be too much, but if you take the time to read and decipher everything here, it will help you understand and choose which oil to use for your car(s). While I am no tribologist, I will try my best to put into words, what I understand about current engine oils. Viscosity is the measurement of an oil's resistance to flow, not its ability to flow. Oil flow is needed to supply lubrication and cooling to an engine. When an engine is designed, its recommended oil viscosity is selected dependent upon the internal operating temperatures of its various engine parts. The only problem with oil viscosity is, at different ambient temperatures, the viscosity changes. At lower temperatures, viscosity is higher; at higher temperatures, viscosity is lower. Before an oil is rated, it is tested at 100C/212F for the low number, and at 40C/104F for the high number. A Viscosity Index (VI) is then calculated for the oil from its viscosities at the low and the high end. The VI tells us how much the oil's viscosity changes from 40C to 100C. A higher VI means the oil is more stable (does not change much) and is a better oil. So what does this mean then? We want an oil with a viscosity that does not change much when the temperature changes. Sounds counterintuitive, right? I thought we wanted an oil that flows better when cold and sticks to engine parts when hot. Remember, this is the base oil we're talking about. Base oil is what you start out with, and the least amount of change is better with base oils. More on that later. Allow me to go into more background information. As I stated in one of my other posts, lubrication can be divided into two categories, hydrodynamic and boundary. Hydrodynamic is the liquid barrier that comes from a layer of oil between two moving parts. Sooner or later, that hydrodynamic layer fails. Direct metal to metal contact is rare and is usually momentary, but that wear is cumulative. That's where the boundary lubrication comes in. Boundary is created by a higher viscosity oil that stays in place longer (sticking to parts) and creating a protective surface for the parts to slide. In order to create this boundary lubrication layer, additives are added to the oil. At the same time, it is the additives that make oil multi-viscosity. It is the various types of additives that manufacturers combine with the base oils that produce the multi-viscosity-ness of oils. The problem with oil is, the additives is the weak link. Theoretically, oil itself does not break down; it is the additives that break down. The majority of the contaminants are the acids that are byproducts of the internal combustion engine. As the additives combine with these acids, they form the sludge and gunk that turns your oil to black. Heat also cause the additives to break down. So as more and more additives break down, your oil turns more and more to its pure form, the base oil. That is why your base oil's VI is important in the first place -- it provides a good basis for the additives at the given temperature range. Some more background. Ever since the 1990's, oils have been grouped into five groups, Group I through Group V. Groups I through III are refined from petroleum; Group IV also come from petroleum, but in a very different way; and Group V oils come from other sources than petroleum. Just real brief, the lower the Grouping, the less pure the oil. Group I is the least pure, and it contains your gear oils. The higher the Grouping, however, the less additives the oil can hold. And because it is the additives that break down (not the oil, remember?), the longer the higher Grouping oils will last. Group III contains most of the "synthetic" oils using the new post-lawsuit definition of synthetic. These are not man-made, but purified from petroleum. Group IV's come from the purest part of the petroleum refining process, the gasses. Royal Purple, Mobil-1 and Amsoil all fall into Group IV. Group V oils are made from vegetable oils and animal oils and contains the Redline brand. Now, if you have been car-shopping lately and bought a late-model car, you will notice oil change intervals of 15,000 miles (entry-level vehicles) to 75,000 miles (high-end cars such as Porsche). There are several reasons why these cars can go so long between oil changes. They all require synthetic oils (Group III or Group IV). Why? It's not a marketing trend (if it ever was); it's a federal requirement. Huh? With the EPA's passage of OBD II emissions (updated OBD II, not 96+ OBD II), manufacturers have engineered their vehicle's engines to use oils that contain less additives. One of the requirements of the OBD II system is to light up the infamous Check Engine Light when there is oil contaminants. Exactly what that means, I do not know. However, I do know that if the engine oil is too old, the CEL light will come on. It is because of the EPA and OBD II that oils being manufactured today contain less and less additives. The manufacturers are secretly removing (or just not adding) the additives from their oils. What does this mean? This means, while we think we are doing our engines good by servicing our cars with late-technology oils, we are actually doing more harm. That is, if our engines were not designed to use this late-technology oil in the first place. Our VG30DETT was not. By using newer oils, we missing the vital additives our Z's need and over time, causing more harm than good. How can we help? Use the "High Mileage" oils. It is not a marketing strategy by the oil manufacturers, as some may have been lead to believe. Only the "High Mileage" oils contain the right amount of additives the engines engineered prior to 1990 requires. I hope this lesson in oil technology helps you choose your oil for your next oil change. FAQ So does that mean I should continue using Mobil 1, Royal Purple, Redline?
Because the oils used by most fanatics here fall into Group IV (Royal Purple, Mobil 1, Amsoil) or Group V (Redline motor oil only), it is worthy to revisit this subject. Because these oils are not good at retaining additives, they are manufactured with relatively less additives. That means there are less additives to combat the acids produced from the internal combustion process. Most people here change their oil between intervals of 3000 miles to 5000 miles, so as long as you follow those guidelines, your level of additives should be okay. What about oils marketed as "Racing Oil"?
Racing oils are produced to be used and changed after every race, so these types of oils contain the least amount of additives. They are also made to run on a small temperature range. This oil is not recommended for use for a vehicle that is driven on a daily basis as its low level of additives will be depleted quickly. I just bought a new car that has an oil change interval of 15,000 miles. Can I change it at 3500 miles?
Yes, you can, but just note that depending on which type of oil you use, you may void your warranty. Depending on vehicle manufacturer, they may have scheduled maintenance intervals that include oil changes. If the dealer sends in the oil for testing during the oil change and finds out you did not use the proper oil, your warranty may be voided. Remember to use the recommended oil type.
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