FINESSE 1 -2 -3
Slippery Finesse: Be a Lubrication Pro
WHAT DO YOU CALL A PERSON TRAINED AND EDUCATED IN THE ART AND SCIENCE OF LUBRICANTS AND THE REDUCTION OF FRICTION IN MOVING PARTS? A TRIBOLOGIST. NO, WE’RE NOT GOING TO GIVE YOU A TRIBOLOGY DEGREE, BUT THE NEXT THREE EPISODES OF FINESSE WILL GIVE YOU ENOUGH INFO TO MAKE YOU DANGEROUS AT THE LOCAL QUICK LUBE!
SYNERGY — The Big Picture Synergy is all about making the ingredients in a lubricant hold hands and sing Kumbaya. The base oil and additives must be compatible with each other and for their given application. Don’t get caught in the trap of cherrypicking individual elements of an oil’s makeup and then use them to claim one oil is better than another. Compare the whole product, and its performance, not just its individual components.
VISCOSITY — It’s All About Flow Viscosity is the measurement of an oil’s resistance to flow. Oil flow is needed to supply lubrication and cooling. When a powerplant is designed, its recommended oil viscosity is selected based on a specific oil temperature (usually around 200 degrees Fahrenheit) related to the internal characteristics of the engine, such as bearing clearances. The problem is that oil has different flow characteristics depending on temperature. When cold (and by “cold” we include room temperature), it is “thick” (higher viscosity). When hot, it is “thin” (lower viscosity).
If you look at the viscosity table nearby, you’ll see that there are a lot of ways to measure oil viscosity. Tribologists commonly use centistokes (cSt) or Saybolt Universal Seconds (SUS), which are very fine graduations. Another unit of measurement is the centipoise (cP), which is not shown on the chart. There is a difference between a precise measurement of viscosity and a viscosity grade. SAE grade 30 oil can be within a range of about 9.8cSt and 13cSt at 100 degrees Celsius (about 212 Fahrenheit) These grades make it easier for us to choose an oil.
Because the performance of an oil measured at 40 C (about 104 F) as part of placing it into a grade. Look at the bottom of the SAE grades and you see the “W” designation. This stands for “Winter.” To get a winter designation, the oil undergoes some extra testing and has to meet additional viscosity standards.
A critical viscosity specification for oil is the Viscosity Index (VI). Calculated from its viscosities at 40 C and 100 C, it shows how much, or how little, the oil’s viscosity changes according to temperature. A higher number means the oil is more stable as its viscosity does not change much through the given range of temperatures. While the VI of an oil can be improved with additives, called Viscosity Index Improvers (VII), the best results come when the base oil has a high VI. Otherwise, as the additives break down, the oil begins to lose viscosity.
LUBRICATION — The Guardian Distilling it down to the simplest terms, 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. Fluids don’t compress, as you found out the first time you bellyflopped into a pool, but lube oil does leak out from the sides of bearing surfaces. Heavy loads speed that process and things get worse as parts wear and clearances increase. That’s why a continuous flow of oil is needed at the right viscosity according to the oil temperature.
The flow of oil needed for hydrodynamic lubrication can come from a pressurized system, as with engines, transmissions and many transfer cases, or from splash, as with some older transmissions and transfer cases, and with all drive axles. The splash fed stuff usually uses a higher viscosity oil that stays in place longer, but relies more on the boundary lubrication from various Extreme Pressure (EP) additives. That’s especially true in axles. Oil viscosity is important to keeping the oil in place. If it’s too low for the bearing clearances, or the load, it squirts out too quickly. A higher flow of oil may help, but good hydrodynamic lubrication is a combination of the viscosity and oil flow. As parts wear and bearing clearances increase, it’s sometimes necessary to increase the viscosity to keep things in balance.
Sooner or later, that hydrodynamic layer fails. Direct metal to metal contact is rare and is usually momentary, but the wear that occurs is cumulative. That is where boundary lubrication comes in as a backup. Boundary lubrication comes from the additives and the last bit of oil film. Additives like moly, boron, and PTFE (Teflon) maintain that microscopic barrier. It may only be a few molecules thick, but that layer is the last defense against wear.
The opportunities to improve the service life and performance of your 4x4 via upgrades in lubrication are many. In this three part series, we’ll give you the 101 class on lubricants and how to use them with maximum effect.
Viscosity can be measured in a number of ways and this chart shows some of them and it gives you a rough conversion from one to another. Note also the viscosity grades, which are not measurements. The SAE grades engine and gear oil differently, with SAE 90 gear oil having about the same viscosity as SAE 50 engine oil. AGMA (American Gear Manufacturers Association) has a very simple system. The ISO (International Organization for Standardization) has another system with fairly fine graduations. SAE is the recognized authority when dealing with automotive stuff, but ISO is most common in industry.
BASE OIL — The Foundation Any liquid lubricant is only as good as the sum of its base oil and its additives. Base oil is like the water used to brew coffee. Water makes up most of the drink. Coffee, cream and sugar are the additives. If you get water from a muddy puddle, you’ll get nasty coffee. Insist on using that nasty water and you’ll have to put in more additives to make it palatable. Better coffee, cream and sugar (higher quality additives) helps too. Same with oil. The better the base oil, the fewer additives are needed. The fewer the additives, the longer the oil will last because additive breakdown is one of the major reasons we have to change the oil in the first place.
Since the early ’90s, base oils have been classified by the American Petroleum Institute (API) into five categories (below). Groups I through III are refined mineral oils (meaning from petroleum). The Group IV base oils are also engineered from mineral oils but in a very different way. Group V oils come from other sources.
Group I: These are the least pure oils out there and are refined with the older tech methods that have been around since oil day one. When Chevron invented Hydrocracking in 1959, it drastically improved the refining process. Even so, Group 1 oils still contain more waxes, sulfur and other impurities than do the more highly refined oils. As a result, they also oxidize (degrade) faster and their lower resistance to vaporization (being burned) is not conducive to low emissions.
The waxes give them poorer cold weather flow characteristics. The VI of Group I oils is seldom much above 90 and this makes them suitable only in a narrow range of temperatures without a lot of blending. There are Group I+ oils with VIs over 100. Group 1 oil is no longer common as a primary ingredient of motor oil because of the new emissions standards and the availability of lower cost Group II and III refining processes. You still see it in gear oils. If group 1 oils have any plusses, it’s that they have very good additive retention.
Group II: These are more pure oils that began appearing in the early ’90s after Chevron further improved the refining process with Iso-Dewaxing. These base oils generally have VIs around 100 and are better suited for use in multigrade oils. Group II+ oils were also developed late in the ’90s and these have VIs between 100 and 120. There is very little sulfur and few impurities in Group II.
Group III: These came on the market in the late ’90s and are extremely pure oils with VIs above 120 and they feature a very uniform molecular structure. Group III oils are so highly refined that they can now be legally called “synthetic.” There is debate and angst in traditional synthetic oil enthusiast camps over this, but the facts are that Group III oils match within 90-plus percent, the performance of Group IV synthetics (see below). Since the definition of “synthetic” was settled in a lawsuit, the majority of the synthetics out there now use Group III base oils. Development has been rapid in this group, with some new refinements leading up to Group III+ designations and VIs exceeding 140. The Group IV base oils still hold the edge in cold temperature performance, a much lower cost to produce. There is virtually no sulfur in Group III oil.
(Left) Mineral Oil (Right) Synthesized Hydrocarbon. These graphics show the differences on a molecular level between refined mineral oil and synthetics, a.k.a. synthesized hydrocarbons. Note the uneven sizes of the molecules in the mineral oil. The smaller and less stable elements will break down, oxidize and be consumed sooner than the larger, more stable ones. The more even structure of the synthetic provides a stronger defense against oxidation and burnoff because all the weak and volatile elements are gone. Kinda like being able to pick a football team by going back in time and getting all the best players in their prime, as opposed to getting a random selection of players that include good, decent and so-so players. Which team do you think will win?
Group IV: These are the traditional polyalphaolefin (PAO) based synthetics. They are “engineered” oils but they still come from mineral oil, albeit from the purest part, the gasses. They cherry pick certain sized molecules to form uniform chains and the results are very temperature stable (high and low temps) oils with excellent lubrication qualities. Even though the processes have been around since WWII, they are expensive to produce. PAO base oils typically require fewer additives than do most other types, which solves the problem of additive breakdown.
Group IVs are extremely resistant to oxidation, so they can last a very long time. Recently published figures from Chevron show that PAO base oils are about 40 percent more resistant to oxidation than Group III, but some of the newest Group III+ oils are within about 17 percent. Anti-oxidant additives typically provide the “equalizer” in all formulations, but again, the fewer additives needed the better. Today, there are fewer oils produced with PAO base stocks. Royal Purple, Mobil-1 and Amsoil are some of the better-known brands. Group IV base oils typically have VIs from 120-150. If group IV oil has a downside, it would be additive retention. To counter this, small amounts of Group I are added to help carry the additive packages.
Group V: The API puts lots of different oils in this category as kind of a catchall, but to most oil enthusiasts Group V means esters (a.k.a. diester or poleoesters) derived from vegetable and animal oils. From these substances, very uniform molecular chains are formed. Group V oils are often used as detergent additives to PAO and mineral based oils. A few oils have been made from mostly Group V stocks, one well known brand is Redline. Group V base oils have VI’s in the 140-150 range. Base oil comes in a variety of viscosities. If you wanted to make a straight SAE 30 oil, you’d use an ISO 100/12 cSt oil (in the SAE 30 range) and the oil would be very resistant to viscosity changes. With a multigrade made from mineral oils, they usually start out with an oil closer to the “W” rating and add VIIs to make the oil viscosity increase as it heats up. The SAE 10 base oil then acts like an SAE 30 or 40 oil at operating temps. The more the difference in viscosity from the W-number and the high temp number, the more VIIs are used. The problem is that VIIs break down with time and the oil gradually loses viscosity. PAO and Group V ester synthetics typically need few, if any, VIIs so they hold viscosity better.
GEAR OIL SERVICE CLASSIFICATIONS
GL-1 Outdated. This is a light duty oil used in manual transmissions. You don’t want to put this in an axle.
GL-2 Outdated. This classification was used for worm gear axles and manual transmissions.
GL-3 Outdated. It was used in manual transmissions in moderate to severe conditions, or spiral bevel
axles in mild to moderate conditions.
GL-4 Current. For spiral bevel axles in moderate to severe conditions, or hypoid axles under moderate
conditions. It can also be used in manual transmissions. It has few sulfur and phosphorus additives that
can attack bronze synchros.
GL-5 Current. This oil classification will provide the best overall protection and is EP rated.
GL-6 Outdated. An extreme-duty oil that was used in high-offset hypoid axles or in severe duty classifications.
The modern, improved GL-5 classification largely covers the old GL-6 situations.
ENGINE OIL — Details and Service Categories If you look at a bottle of oil, in addition to the SAE viscosity grade, you’ll see an API service category roundel on the label. These codes indicate the performance standards the oil meets. These standards are constantly changing, usually in response to ever-more-stringent emissions criteria. Compare these ratings with what the manufacturer of your truck specifies and buy accordingly. If you have an older rig, the guidelines are often backwards compatible and the roundel will so indicate. In the recent past, the newer oil was almost always an improvement on the old and was fully backwards compatible. That’s not so definite any longer. Today, the imperatives have to do with some of the additives that were designed to keep older engines alive and well or replacing them with more environmentally friendly additives. The jury is still out on these and you can read more in Part 2 next month.
The API Starburst signifies the oil manufacturer has submitted the oil to the API for actual tests rather than merely complying with the standards. After demonstrating the oil meets the standards, it’s given the starburst. It’s an expensive process to get certified and the money is spent whether or not the oil passes.
GEAR OIL — Details and Service Categories Gear oil often starts out with the same type of base oil as engine oil. Because impurities are less of a hazard in an axle or gearbox, you see more Group 1 and II oils used, but you also see Group III and Group IV and V as well. Most often, it’s a mix. Look again at the viscosity chart to see how gear oil SAE viscosities relate to SAE engine numbers. Gear oil also has service categories, GL 1-6 (see Sidebar). Basically, just install GL-5 rated oil in all axles.
Many (but not all) GL-5 oils contain a high concentration of sulfur/phosphorus (S/P) EP additives that will attack certain metals, like brass and bronze synchronizers, over long periods. For this reason, you don’t want to use GL-5 in a manual trans that takes an SAE 90. The GL-4 grade is suitable for transmissions. Some synthetic GL-5 gear oils contain little or no S/P and are safe for transmissions.
The API donut shows the SAE viscosity and the service standard the oil is designed to meet. Compliance with the standards is voluntary but seldom does a major manufacturer try to cheat.
ATF — Details Again, ATF starts out the same way as any other oil, with a base oil of the correct grade. Most ATF that’s formulated for the newest transmissions is Group II or III and most ATF is in the SAE 20 range, with some being SAE 10W-20. There are a bazillion different formulations from the various different manufacturers. In many cases, it is hyper-critical to use what’s specified for your truck. The differences lie mostly with the additives and sometimes with the viscosities.
WHY GOOD OIL GOES BAD Base oil essentially never goes bad unless it’s heated to incredible temperatures. In that case, you’ll have had other warnings that something’s wrong! In theory, you could use a base oil for the lifetime of your truck. The additive packages are the first weak link. They eventually wear out and the level of contaminants builds up as the additives designed to fight them are depleted. These include acids that are a chemical reaction to the combustion process and are normally negated by the additives, as well as various solid particles too small for the oil filter to catch. It really is as simple as that.
Next Time: How to pick a good oil and how to pick a good oil filter.
SOURCES
American Petroleum Institute
www.api.org
Royal Purple
www.royalpurple.com
Shell Rotella-T
www.shell.com