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Since Ive been writing this column, I have received a lot of e-mails with questions about various subjects related to engine oils. Thats good on two fronts: First, it means that you are reading the column, and second, the articles are stimulating your curiosity about some subject or issue. I thank you for your interest. I thought Id take this months column to address some of the questions and try to provide some more extensive answers.

Q. How are engine oils evaluated to meet API and ILSAC categories?

When the oil industry and automakers decided that a set of standards was needed to quantify engine oil performance, they agreed on a series of tests to demonstrate oil performance in very specific areas, such as preventing wear, battling sludge and deposits, and maintaining the correct viscosity. Many of these tests are referred to as engine sequence tests, because they put the oils through their paces using gasoline- or diesel-fueled engines under controlled conditions.

The most current gasoline engine sequence tests, demonstrating that a passenger car engine oil meets the newest ILSAC GF-4 and/or API SM categories, are shown in the table below, along with some of the laboratory bench tests that also must be passed.

Each of these tests is managed by ASTM to be sure it is repeatable and reproducible. The tests are run at accredited laboratories and are regularly tested with reference oils to be sure the test has not changed. In addition, standardized fuels are used for each test and certified by ASTM before labs can begin using them.

(Hint: You can often spot an industry newcomer because he or she will mispronounce engine test names. All engine sequence tests use Roman numerals followed by a letter showing the current version in use. So the Sequence VIB is not the v.i.b. or vib test, but the Six-B; Sequence VG is not the veegee but the Five-G.)

Q. What is meant by base oil interchange?

This is one area that is sometimes difficult to understand. This set of guidelines allows oil marketers and additive suppliers to use the successful test results from one engine oil formulation to qualify another oil using similar (but not exactly the same) base oil. This is based on similarity of base oil properties. The American Petroleum Institute developed a set of parameters to describe various base oil types; if the base oil alone differs in a formulation, this information is used to decide what tests need to be run again, or which may be skipped. The five API base oil groups are shown in the table below.

It all seems pretty complex – and it is. However, by continually reviewing data and test methods the industry has gotten a good handle on what it takes to demonstrate that an engine oil will perform according to recognized industry requirements – even if a change must be made in the base oil used to manufacture it.

Q. What is viscosity grade read-across?

This is another area which is used to approve products based on other test data. Viscosity grade read-across recognizes that certain viscosity grades are more difficult to qualify (lower multi-grades for example). If a test program is completed in one grade – a 10W-30, for example – much of the test data can be used to demonstrate performance in other viscosity grades. Again, continuous review of the data and test methods has allowed the oil, additive and engine manufacturers to be confident of the test results.

Q. What are synthetic oils? Are they better than conventional oils?

Looking at the API base oil categories below, you can see that Group IV is reserved for polyalphaolefins (PAO). These were the classic synthetic base stocks used by many engine oil marketers. Tailor-made from pure decene molecules, they offer better low-temperature viscometrics and high-temperature performance than conventional oils.

For several years in the 1990s, there was a lot of debate whether highly refined Group III mineral oils also could legitimately claim to be synthetic. Adherents stressed that Group III base oils could be produced either by severe hydrocracking or by polymerization of certain low-molecular-weight hydrocarbons (a synthesis process). For the U.S. market, the issue was settled by the Advertising Division of the Council of Better Business Bureaus, which upheld Group III as entitled to call itself synthetic.

Since then, a number of marketers who formerly used PAO switched in whole or in part to Group III base oils, for cost reasons. And why not? For engine oil applications, there is no significant performance difference between PAO and Group III, although PAOs hold the advantage in the low-temperature arena.

So are synthetic oils better? The only answer is, Not necessarily. Comparisons are difficult because when it comes to engine oils, theres no accepted technical definition for synthetic. And remember, the additive technology in play can also equalize the differences.

Q. Can older vehicles which have operated on higher-phosphorus-containing engine oils perform satisfactorily on the new, lower-phosphorus engine oils now in the marketplace, such as SL and SM?

One of the criteria for acceptance of any new engine oil category is that it be backward compatible with older specifications. That is, API SM oil must meet all of the requirements of API SL or earlier oil. SL had to meet the requirements of SJ and earlier, and so on.

This backward chain is partially accomplished through the use of reference oils that met older test requirements. However, there is some engineering judgment that is also applied. That simply means that the performance of certain engine oils can be said to be equivalent to older oils by comparing similar chemistries, but not necessarily the same chemistry in critical (although not identical) engine tests. It is an accepted practice and is recognized worldwide.

Q. Why do we use zinc dialkyldithiophosphate (ZDDP) when the phosphorus in it is known to contaminate catalysts on vehicles and reduce their efficiency?

The simple answer to that is that there is nothing that has been found that gives as much bang for the buck as ZDDP. Other compounds are used now to provide added antiwear and antioxidant performance, since ZDDP has been reduced in dosage in API SM and ILSAC GF-4 engine oils. With the next generation of engine oils, called ILSAC GF-5, on the horizon, the level of phosphorus is not going higher. In fact, the industry is working on a method to measure the impact of the oils phosphorus on catalyst systems for GF-5.

Q. How about solid components in engine oil? Is it a good idea to use molybdenum disulfide or graphite or even Teflon as friction modifiers and antiwear agents?

To date, no solids suspension systems have been developed for engine oils which will totally prevent the dropout of the solid material. Ultimately, the oil pan is the final resting place of such materials, and there isnt much use for friction modifiers in the pan!

Q. Whats the ideal interval for changing your oil?

The question of oil drain intervals has occupied a lot of the queries Ive received. Each writer has been adamant about his practice and/or product. Some synthetic oil marketers believe that their oils can go 15,000 miles or more before change. They have field test data which they believe proves the point. Others are very comfortable with 3,000-mile drains based on their belief that an ounce of prevention is worth a pound of cure.

Quick-lube groups support the shorter drain intervals as do most car dealers. For those of us who have an on-board oil monitoring system, the vehicle tells us when its time to change. My General Motors vehicle uses its Oil Life System, which monitors time, temperature, average speed and other engine conditions to decide when to change the oil. Some more sophisticated systems also measure some oil properties. Whatever your views are on this subject, you should use good judgment so your second-largest expenditure in life is well protected and gives you long and carefree performance.

Q. Whats being done about used oil disposal?

This is a very serious issue, as it was determined a number of years ago that used engine oils were hazardous and should not be handled or disposed of carelessly. For those of us who let others change our oil (do it for me), the problem is not ours but we do pay for it. Just look at your next bill.

For the Do It Yourself crew, finding a place to dispose of used oil properly is not too hard. Many facilities that change oil have a used oil container (a drum or a bulk tank) and should allow you to dispose of your oil there. Please dont decide that it would be OK, just this once, to dump it down a storm drain or pour it along the fence line to control weeds, or pour it on a fire-ant mound! Visit www.earth911.org to find a site nearby that will accept your oil – its that easy. Proper disposal is a responsibility that we all share and should take very seriously. The water you drink tomorrow will thank you!

There have been lots of other questions, but these are the ones that seem to be most on peoples minds. I hope that Ive shed a little light on each subject, and also hope that you continue to read, question and hopefully enjoy what you see here.

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