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Just about all oil now is hydrocracked, or at least partially. What it is basically is Group 1 base stocks (traditional mineral oil) had the wax separated out, usually by chilling it. Group 2 base stock is hydrocracked. The wax is still in the oil, but broken down to where it's usuable. With stringent new regulations that the EPA has put on OEMs, including EGR, pretty much everything is Group 2, or partially. Group 2 has advantages of better lubrication, high viscosity index and cold flow. But they don't hold additives worth squat. The traditional mineral based hold additives very well. Because the Group 2s don't hold additives well, usually this rules out any extended oil drain program. What many manufacturers do, including Mobil, is blend Group 1s and Group 2s. This gives them the increased lubricity, higher viscosity index and improved additive performance. Add these up, and you have an extended drain oil. Group 4s are your synthetics. Chances are, if it's crystal clear, that its a straight Group 2 oil. Clear as mud? Here is a general explanation stolen from the internet: Group I - Solvent Freezing: Group 1 base oils are the least refined of all the groups. They are usually a mix of different hydrocarbon chains with little or no uniformity. While some automotive oils on the market use Group I stocks, they are generally used in less demanding applications. Group II - Hydro processing and Refining: Group II base oils are common in mineral based motor oils currently available on the market. They have fair to good performance in lubricating properties such as volatility, oxidative stability and flash/fire points. They have only fair performance in areas such as pour point, cold crank viscosity and extreme pressure wear. Group – III Hydro processing and Refining: Group III base oils are subjected to the highest level of mineral oil refining of the base oil groups. Although they are not chemically engineered, they offer good performance in a wide range of attributes as well as good molecular uniformity and stability. They are commonly mixed with additives and marketed as synthetic or semi-synthetic products. Group III base oils have become more common in America in the last decade. Group IV -Chemical Reactions: Group IV base oils are chemically engineered synthetic base stocks. Polyalphaolefins (PAO's) are a common example of a synthetic base stock. Synthetics, when combined with additives, offer excellent performance over a wide range of lubricating properties. They have very stable chemical compositions and highly uniform molecular chains. Group IV base oils are becoming more common in synthetic and synthetic-blend products for automotive and industrial applications. Group V - As Indicated: Group V base oils are used primarily in the creation of oil additives. Esters and polyolesters are both common Group V base oils used in the formulation of oil additives. Group V oils are generally not used as base oils themselves, but add beneficial properties to other base oils. Note that the additives referred to in the Group V description are not aftermarket type oil additives. The additives referred to are used in the chemical engineering and blending of motor oils and other lubricating oils by the specific oil company that produces the finished product.
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