Types of engine oil
See Figures 2 and 3
Engine oil service classifications have been provided by the American Petroleum Institute and include "S" (normal gasoline engine use) and "C" (commercial and fleet) applications. The following chart compares the latest API oil classifications with those previously used.
The American Petroleum Institute (API) SH quality level is a performance upgrade for gasoline engine oils from the API SG category. The American Society for Testing and Materials (ASTM) establishes engine tests for motor oils. Passing limits for these tests are the same for API SH oils as they were for API SG lubricants. However, the Chemical Manufacturers Association (CMA) has applied a Multiple Test Acceptance Criteria (MTAC), which is a statistically based methodology, to ASTM engine tests used to evaluate candidate oil.
The MTAC is:
- For oil run once, test data for each parameter must be a pass.
- For oil run twice, the average value of each parameter must be a pass.
- For oil run three or more times, one test may be discarded, and the average value of retained test data for each parameter must be a pass.
Previously for API SG and earlier categories, a pass in each engine test was sufficient regardless of the number of failures on the candidate oil before a test pass was obtained. Therefore, oils could be approved by failing a number of tests and bouncing one through for a pass.
In order to be certain that API SH oils can pass the ASTM engine tests to which MTAC have been applied, higher additive levels and a balancing of the chemical additive formula are required. More highly refined base oils are also helpful in meeting API SH specifications. The MTAC applied to ASTM engine tests results in performance improvements outlined below.
Test criteria (how oils are rated)
- Engine Rust
- High Temperature Oil Oxidation (oil deterioration)
- Piston Varnish
- Engine Varnish
- Engine Sludge
- Cam & Lifter Wear
- Bearing Wear
- Fuel Economy Improvement
Performance Improvement Over API SG
- Less rust
- Improved oxidation protection
- Less varnish
- Less sludge
- Less wear
- Better, fuel economy
Passing the ASTM Sequence tests with performance improvements over API SG allows oil to be labeled API SH and display the API donut symbol.
Thus far, we've discussed API SH. Now we'll talk about the tie-in with ILSAC. The American Automobile Manufacturers Association (AAMA) and the Japanese Automobile Manufacturers Association (JAMA), through an organization called the International Lubricant Standardization and Approval Committee (ILSAC), jointly developed and approved a specification for gasoline-fueled passenger car engine oils identified as GF-1. API and ILSAC have agreed on a single set of specifications that meet both API SH and ILSAC GF-1 with the exception of fuel economy and SAE grades approved. That is, in order to meet GF-1 an oil must meet API SH and the Energy Conserving II (EC-II) requirements. EC-II oil provides a 2.7% fuel economy improvement over reference oil in an ASTM fuel economy test that uses a laboratory engine. API SH has no energy conserving requirements. ILSAC GF-1 specifications apply to OW-X, 5W-X and 1OW-X oils where X can be 20, 30, 40 or 50. In contrast, API SH applies to all viscosity grades (multigrades and monogrades).
Shown in the illustration are the ILSAC Certification Mark and the API Donut Symbol. The ILSAC Certification Mark must be displayed on the front of an oil container. An oil with the ILSAC Mark meets all physical, chemical and performance requirements (ASTM engine tests) of API SH and is Energy Conserving II. Its viscosity grade is OW-X, 5W-X or 1OW-X.
The API Donut Symbol can be displayed anywhere on the container for oils meeting the API SH chemical, physical and performance requirements. All viscosity grades are included and the oil does not have to be EC-II approved.
API designation SH and ILSAC designation GF-1 were introduced by the petroleum industry on August 1, 1993.
The API designation SJ has been adopted to engine oils available after 1996 and has replaced the former SH designation at the time of publication. The API SH designation may still be used in conjunction with an API C-service category.
Previously there were two energy conserving oil categories:
ENERGY CONSERVING AND ENERGY CONSERVING II: These may appear on the label as: EC or EC II. Effective as of October 1996 there is only one EC designation that is EC. The EC and EC II that were used in conjunction with API Service Category SH became obsolete after August 1997.
EC used in conjunction with API SH: These oils have produced a fuel economy improvement of 1.5 percent or greater over a standard reference oil in an ASTM test procedure. Oils meeting this requirement display the ENERGY CONSERVING will have a label in the lower portion of the donut shaped API Service Symbol.
EC II used in conjunction with API SH: These oils have produced a fuel economy improvement of 2.7 percent or greater over a standard reference oil in an ASTM test procedure. Oils meeting this requirement display the ENERGY CONSERVING II will have a label in the lower portion of the donut shaped API Service Symbol.
EC used in conjunction with API SJ: These oils have produced a fuel economy improvement of 1.4 percent or more (0W-20 and 5W-20 viscosity grades), 1.1 percent or more (other 0W-and 5W-multiviscosity grades), or 0.5 percent or more (low-multi viscosity grades and all other viscosity grades). Oils that meet this requirement and are properly licensed may display "Energy Conserving" in the lower portion of the API Service Symbol in conjunction with API Service Category SJ in the upper portion.
Oil viscosity
See Figure 4
In addition to meeting the SH or SJ classification of the American Petroleum Institute, your oil should be of a viscosity suitable for the outside temperature in which you'll be driving.
Oil must be thin enough to get between the close tolerances of the moving parts it must lubricate. Once there, it must be thick enough to separate them with a slippery oil film. If the oil is too thin it won't separate the parts, if it's too thick it can't squeeze between them in the first place either way, excess friction and wear takes place. To complicate matters, cold-morning starts require thin oil to reduce engine resistance, while high-speed driving requires thick oil, which can lubricate vital engine parts at temperatures up to 250°F (121°C).
According to the Society of Automotive Engineers' viscosity classification system, an oil with a high viscosity number (e.g., 40) will be thicker than one with a lower number (e.g., l0W). The "W" in l0W indicates that the oil is desirable for use in winter driving. Using special additives, multiple-viscosity oils are available to combine easy starting at cold temperatures with engine protection at turnpike speeds. For example, 10W-40 oil will have the viscosity of l0W oil when the engine is cold and that of 40 oil when the engine is warm. The use of such oil will decrease engine resistance and improve your gas mileage during short trips in which the oil doesn't have a chance to warm up.
Some of the more popular multiple-viscosity oils are 5W-30, 10W-30, 10W-40, 15W-40, 20W-40, 20W-50, and 5W-50.
Consult your owner's manual or a reputable oil dealer for the recommended viscosity range for your car and the outside temperature in which it operates.
Additives
See Figures 5 and 6
High-quality engine oil will include a number of chemical compounds known as additives. These are blended in at the refinery and fall into the following categories.
Pour point depressants help cold starting by making the oil flow more easily at low temperatures. Otherwise, the oil would tend to be a waxy substance just when you need it the most.
Oxidation and bearing corrosion inhibitors help to prevent the formation of gummy deposits which can take place when engine oil oxidizes under high temperatures. In addition, these inhibitors place a protective coating on sensitive bearing metals, which would otherwise be attacked by the chemicals, formed by oil oxidation.
Rust and corrosion inhibitors protect against water and acids formed by the combustion process. Water is physically separated from the metal parts vulnerable to rust, and corrosive acids are neutralized by alkaline chemicals. The neutralization of combustion acids is an important key to long engine life.
Detergents and dispersants use teamwork. Detergents clean up the products of normal combustion and oxidation while dispersants keep them suspended until they can be removed by means of the filter or an oil change. Foam inhibitors prevent the tiny air bubbles that can be caused by fast moving engine parts whipping air into the oil. Foam can also occur when the oil level falls too low and the oil pump begins sucking up air instead of oil (like when the kids finish a milkshake). Without foam inhibitors, these tiny air bubbles would cause hydraulic valve lifters to collapse and reduce engine performance and economy significantly.
Viscosity index improvers reduce the rate at which an oil thins out when the temperature climbs. These additives are what make multiple-viscosity oils possible. Without them, single-weight oil, which permitted easy starting on a cold morning, might thin out and cause you to lose your engine on a hot afternoon. If you use multiple-viscosity oil, it's this additive that helps your gas mileage during those short trips in cold weather.
Friction modifiers and extreme pressure additives are valuable in so-called boundary lubrication, where there is metal-to-metal contact due to the absence or breaking down of the oil film between moving parts. Friction modifiers, or anti-wear agents, deposit protective surface films that reduce the friction and heat of metal-to-metal contact. Extreme pressure additives work by reacting chemically with metal surfaces involved in high-pressure contact.
Figure 6 Typical breakdown of the additives in a bottle of motor oil.
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Synthetic oils
See Figure 7
There are excellent synthetics and fuel-efficient oils available that, under the right circumstances, can help provide better fuel mileage and better engine protection. However, these advantages come at a price, which can be significantly more expensive than the cost per quart of conventional motor oils.
Before pouring any synthetic oils into your car's engine, you should consider the condition of the engine and the type of driving you do. Also, check the manufacturer's warranty conditions regarding the use of synthetics.
Generally, it is best to avoid the use of synthetic oil in both brand new and older, high mileage engines. New engines require a proper break-in, and the synthetics are so slippery that they can prevent this. Most manufacturers recommend that you wait at least 5000 miles (8000 km) before switching to a synthetic oil. Conversely, older engines are looser and tend to loose more oil. Synthetics will slip past worn parts more readily than regular oil. If your car already leaks oil (due to bad seals or gaskets), it will probably leak more with a slippery synthetic inside.
Consider your type of driving. If most of your accumulated mileage is on the highway at higher, steadier speeds, a synthetic oil will reduce friction and probably help deliver fuel mileage. Under such ideal highway conditions, the oil change interval can be extended, as long as the oil filter will operate effectively for the extended life of the oil. If the filter can't do its job for this extended period, dirt and sludge will build up in your engine's crankcase, sump, oil pump and lines, no matter what type of oil is used. If using synthetic oil in this manner, you should continue to change the oil filter at the recommended intervals.
Cars used under harder, stop-and-go, short hop circumstances should always be serviced more frequently, and for these vehicles, synthetic oil may not be a wise investment. Because of the necessary shorter change interval needed for this type of driving, you cannot take advantage of the long recommended change interval of most synthetic oils.
Most synthetic oils have been tested under the types of extreme conditions that you hope you will never duplicate within your engine. Under conditions of extreme heat, these oils can offer an additional level of protection which you cannot find in most conventional oils. Because of this, synthetic oils are popular for applications such as towing, racing or desert operation. They are also popular with those who are looking for that extra level of protection against engine wear or damage. Consider all of these factors if you are thinking about using synthetic oils.
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