Issue link: http://read.dmtmag.com/i/859318
Engine Oils Background & Properties castrol.com/GPS 800 255 4417 May 2025 GPS Industry Specifications enhance finished lubricant characteristics. Different refining techniques work to remove unwanted char- acteristics and improve upon desired ones, like viscosity index and oxidation control. Most of Castrol's finished lubricants are blended with Group II base oils and a premium-performing additive package. • Two other categories of fluids are common—synthetics or Group III/Group IV and specialized fluids, or Group V. For engine oils, synthetic fluids fall into two categories: refined and polyalphaolephins. • Refined Group III base oils are petroleum fluids that undergo extreme refining techniques, producing a base fluid with characteristics of a man-made synthetic. Group III refined base oils are typically found in partial to full synthetic finished lubricants, since they have greater than 90% saturates (usually 99%+) and VIs over 120. ey have low pour points, good oxidation resistance, and low volatility. • Group IV base oils are known as polyalphaolefins (PAO). PAOs, the most widely used of the engineered base stocks, consist of all saturated hydrocarbon structures and contain no unwanted sulfur or other metals. Free of wax, PAOs have very low pour points and typically have VIs of 140. PAOs have good thermal stability, but are sometimes difficult to blend with additives. Despite their noted performance features, PAOs are sometimes cost-prohibitive for users. • Group V base fluids consist of other fluids that are not typically derived from oil refining or PAO synthesis, predominately esters and polyolesters. ere are also aromatic and naphthenic base oils that are not suitable for use in heavy-duty engine lubricants due to their poor oxidation stability and low VIs. Aromatics contain elevated levels of sulfur (which lead to deposit formation) and sometimes nitrogen (which contributes to oxidation and deposit formation). Aromatics are typically used as solvents, cleaners, and process oils, and in further chemical reactions for industrial products. • Naphthenic fluids, typically, have low to medium VIs of up to 60. ey exhibit very low pour points, high solubility, and excellent cold flow in long term storage. Naphthenics are commonly used in refrigeration lubricants, metalworking oils, greases, and as extreme cold temperature fluids, such as snowplow oils. Refining Techniques Group I and II mineral-based fluids are all refined from crude oil, and the way that crude oil is refined determines its place in the base oil groupings. Solvent refining is older technology that is oen used to create Group I base stocks. A solvent refined crude oil is dissolved in solvent, then chilled and filtered to remove wax. e resulting base fluid will still have poor low temperature fluidity and a typical VI of 90 to 100. To further influence a base oil's performance characteristics, additional refining using hydrogen may be performed. ere are basically three types of hydrogen refining, each more potent than its predecessor: Hydrofinishing forces pressurized hydrogen into a solvent extracted base oil. e hydrogen molecule fills some of the active double bonds in the hydrocarbon molecule so these molecules cannot react with oxygen molecules to begin the process of oxidation. Hydrofinishing also removes some of the sulfur, nitrogen, oxygen, and color impurities present in the solvent-refined base oil. A more severe process called hydrotreating forces hydrogen gas through the base oil, at higher pressures than hydrofinishing, which further saturates the oil with hydrogen molecules. Hydrotreating boosts oxidation stability, increases pour point, and removes even more sulfur and nitrogen from the base oil. A finished lubricant that has been hydrotreated has lower carbon-forming tendencies than hydrofinished or solvent- refined fluids. A21 ecastrof