Automotive Lubricants



First, a confession: I am a card-carrying member of SAE International. Ive worked in the automotive/oil industry for over 50 years, and I am surprised (but not too often) at some of the questions and comments I hear on the subject of automotive engine oils. Many are from consumers seeking to understand the needs of an engine, oil-wise. However, queries also come from people who are involved in the automotive business and are members of SAE.

Recently, SAE has begun an Open Forum on its website with an invitation for members to ask questions and make comments about topics of the day. One of the hot topics is autonomous vehicles; lots of back-and-forth on that subject, which Ill leave for another time. My interest today is with the questions on engine oil.

Before I dive into the mind of SAE engineers, I think its important to note that if there is anything that identifies the oil industry, or any other for that matter, its jargon. If youve been involved in the oil industry, it may be simple to decode engine lubrication. However, if you are not an engine lubrication native, you have innocently walked into a foreign country! Interpreters are critically needed for our industry, and I hope to be able to clear up some of the seeming gibberish that exists.

One basic question raised on the Open Forum regards what all the specifications are and what they mean. For those of us who work or have worked in the lubricants end of the business, the American Petroleum Institute designations are standard. For gasoline-fueled vehicles, APIs Service Categories (SA to SN) and ILSAC specifications (GF-1 to GF-5) define a set of engine oil performance properties that are based on standardized bench and engine tests. There is a similar system In Europe managed by the Association des Constructeurs Europens dAutomobiles or ACEA.

Among the bench tests, viscosity is number one and almost everything else derives from it. Heres what I mean by that:

Viscosity, or what we think of as thickness, is an oils resistance to flow at a given temperature.

By measuring viscosity at high and low temperatures, we can calculate the oils viscosity index, which indicates how much its viscosity changes with temperature.

Volatility-how easily the oil will evaporate at operating temperatures-is indirectly linked to base oil viscosity, too. Generally speaking, the lower an oils viscosity is, the greater its volatility.

Same goes for flash point, the temperature at which the oil gives off enough vapors to ignite in air, and pour point, the temperature at which its too cold to flow at all. Both are generally lower with lighter-viscosity oils.

I think you get the idea. Admittedly, the properties related to viscosity can be modified by the use of additives such as V.I. improvers and pour point depressants, to name a couple of them. Oxidation inhibitors improve the resistance of an oil to high temperatures and catalytic surfaces, and foam inhibitors reduce its tendency to entrain air. However, the fact that viscosity drives these properties seems pretty apparent.

Engine design folks now seem to take viscosity into account when designing engines, but that wasnt always the case. Back not a few years ago, the automakers lubricants people were very frustrated that engines were being developed based on single-grade viscosities (usually SAE 30). In the real world, meanwhile, the car makers were specifying SAE 5W-30 to capture fuel savings.

Engine tests are a different matter than bench tests. They measure various specific properties of the fully formulated oil in actual use. When you look at the current crop of tests for gasoline-fueled engines in North America, you find measurements for oxidation (the Sequence III test); wear (Sequence IV); deposits (Sequence V); fuel economy (Sequence VI); bearing corrosion and viscosity stability (Sequence VIII); low speed pre-ignition (Sequence IX); and timing-chain wear or stretch (Sequence X). Each of these tests has an appetite for a particular portion of the finished oil chemistry.

At any rate, many of the folks on the Open Forum are not conversant with this system. Yet they are concerned with SAE viscosities, base stocks and automaker specifications, and their lack of oil industry knowledge gives rise to confusion and blind spots. When someone speaks of the Sequence Vid fuel economy test (rather than the VI-D, pronounced six-D), you know theyre not from the oil side.

Heres another example of a blind spot from my Pennzoil days: As many major marketers do, Pennzoil carried out consumer research studies, using what are called mall intercepts. The way it worked was that market research people would approach shoppers in malls and ask a few questions to determine if they were appropriate for the survey being conducted.

The shoppers selected were invited to sit in on a brief session to determine what features of motor oil were important to them. Almost without exception three things were cited: Brand name, viscosity and the letters HD on the label. Brand and viscosity are self-evident but HD was a bit less clear. To some participants it meant heavy duty and to others it meant high detergent. In one case a woman wrote to ask that HD be removed from the label: They were the initials of her ex-husband and she didnt want to be reminded of him!

Weve already touched on viscosity. Next comes base stocks. A clarification here: Under API standards, a base stock is defined as any single viscosity oil refined by a lubricants plant. Base oil is the blend of base stocks used to make an engine oil product of a specific viscosity grade. As I said earlier, it looks like a foreign language at times.

The API base oil groups were created by the team that worked on the institutes Engine Oil Licensing and Certification System in the early 1990s, and are largely defined by the level of saturates, viscosity index and sulfur content. These properties give a fairly good description of base stock quality. The purpose of this system was to allow engine oil formulators some needed flexibility in selecting their base oils while at the same time assuring that the engine oils performance wouldnt suffer if different base oils were used interchangeably by blenders. Interchange rules between the groups also minimize the number of engine tests required to certify an additive system for use in the applicable API category.

Many of you are familiar with the API Groups, but just to make it crystal clear Ive put it in chart form below.

The first three groups are refined, mineral oil base stocks. Polyalphaolefins are the sole material in Group IV, while Group V is a catch-all for whatever is left-naphthenics, esters, polyalkylene glycol, etc.

Currently, Group II is the big dog in the refining arena. The reasons are pretty evident: Group II gives a higher yield with improved properties over Group I. Group III has been growing since 1999, when it was blessed by the Better Business Bureaus National Advertising Division as essentially synthetic, and can be more cost effective than traditional synthetics such as PAO or various esters.

Not surprisingly, there is a bit of a bias by the SAE crowd toward synthetic base stocks. Thats partially due to the engineering mindset that anything that is manufactured is better. With regard to base stocks, most of the people posting on the SAE Open Forum assert that synthetics (mostly defined as real synthetics, not Group III) are superior in every way to refined base stocks.

Many believe that PAO has a much higher resistance to oxidation. Its quite likely that synthetics do last longer, but the hard truth is that starting at about 130 degrees Fahrenheit the oxidation rate of all non-additized hydrocarbon oils (including PAO) doubles for every 18 degrees (10 C) of temperature increase. I cant confirm this, but I suspect that all the major-brand synthetic engine oils have a pretty advanced additive system, which helps retard the rate of oxidation.

Speaking of additive systems, many of the forums engineers are unsure as to what actually goes into engine oil formulations. The oils are a complex mix of components designed to improve performance in several areas. Additives have one or more of three functions: They can protect the base oil, they enhance certain properties of the base oil, or they protect various surfaces within the engine.

Again, when I was working at Pennzoil, we had an advertising campaign based on Z-7. Z-7 was the proprietary additive system that made Pennzoil great (my brag). The seven additive components were antiwear, antioxidant, rust preventative, antifoam, pour depressant, detergent and dispersant (I think). The chemical components changed over time, but they always provided the protections the industry needed.

However, things change. First came multi-viscosity oil, which required adding a polymer to alter the viscometric properties of the finished oil. Single-grade oils such as SAE 30 were replaced with multi-vis oils such as SAE 10W-40. With the rise of fuel economy needs, friction modifiers were added and the preferred viscosity grades were lightened to SAE 10W-30, then SAE 5W-30, and on to our current SAE 0W-20.

Additive components are continuously being upgraded and new chemistries are being introduced. As developments in engine design occur, they can (and often do) precipitate a new engine oil performance category. These changes seem to come faster and faster. So it gets more difficult even for us oil folks to keep up.

SAEs Open Forum is a lively discussion site and a lot of interesting topics are brought up. Of course Im interested in engine oil, so I watch and occasionally comment on some of the statements that drift too far from the truth. In fact, I may just write a treatise for the Forum to try to teach these very smart engineers our language. Shouldnt take more than 10 to 20 chapters to get them speaking fluent engine oil. Wish me luck!

Industry consultant Steve Swedberg has over 40 years experience in lubricants, most notably with Pennzoil and Chevron Oronite. He is a longtime member of the American Chemical Society, ASTM International and SAE International, where he was chairman of Technical Committee 1 on automotive engine oils. He can be reached at steveswedberg