Oil Quality
Sal Lubrano asked:
Q: Other than the rating such as SL and SM what makes all the Dino engine oils different? What makes the Autozone 10-30w different which is a buck and change compared to say Castrol 10-30w which is almost $3. Is it just a brand name so you pay for the label or is there differences in the oil? Does anyone here use the cheaper oil?
Sal---------you asked a couple of very good questions------questions that few really have a good understanding of------i thought i'd have one of our engineers post a few thoughts on the subject...............RC
Each of the replies to Sal’s question points to factors that determine oil quality, but getting at the data pertaining to a specific oil is very difficult. Oil manufacturers are very proprietary about their formulations and do not make specific information about base-stock makeup, additive package or final performance characteristics easy to find. If you visit their websites, you may be able to find a data sheet for a specific oil.
Sal is looking for justification for spending money on premium oil for his car, which is an extremely valid concern. It is the truth that the quality of an oil is not tied to its price, which he clearly understands. Putting aside big box retailers for a minute the major factors which determine the price of oil are:
1) In general the larger an oil company, the less expensive an oil of any given quality. The major manufacturers have extremely good oil at excellent prices.
There are some small boutique oil companies which sell good oil (that they do not themselves refine) at high prices.
2) The volume of that exact formulation manufactured. Specialty formulations for racing partly cost more because the manufacturing lots are smaller and more expensive to produce.
Are the boutique oils worth the extra money? The answer lies in your requirements, and this is where the SAE and API rating systems enter the picture.
The API oil rating system has saved the average driver billions of dollars over the years wasted on bad oil and ruined engines. It gives the layman an easy way to verify that an oil meets the very minimum specifications for a specific engine. The API testing which any API rated oil must pass to be certified merely ensures that the oil will pass certain standards using average engines as test beds. Of all oils that pass the API tests, there is a huge variation of performance above and beyond merely passing the test. If your requirement is tougher or different than the average motorist, then you have to look past the API tests to pick out the very best oils in any class.
As the years have passed, the API tests have become progressively tougher to pass, so in almost all respects today’s API SM oils are far superior to 1987’s API SF oil. The person who answered Sal and recommended the SF oil from the big-box store is forgetting that oil passing SF specifications can be very poor by today’s standards in important ways like sludge generation and high temperature stability. At the time it was introduced SF was the best there was but it was actually replaced by SG (a superior formulation in every respect) because of severe sludging problems in certain engine designs (ASTM Fuels & Lubricants Handbook pg. 468). The reason it was suggested was probably because of the low ZDDP level in modern API SM relative to that found in most API SF. ZDDP, however, is only one of many important characteristics of an oil.
Referring to Sal’s question, what makes an oil better than another? The API tests certainly do point to the factors that affect an oil’s performance such as High Temperature Breakdown (Flash Point), Volatility (NOACK), cold weather characteristics (W-rating), and film thickness under High Temperature, High Shear (HTHS), as well as others. The very best oils excel in one or more of these characteristics, sometimes by several orders of magnitude better than others that barely pass the API tests. Here are some tips toward selecting the correct oil:
* For a daily driver the requirements would be much less than for a high perf TR running 30 pounds of boost. Therefore it would be reasonable to use less expensive oil in that daily driver.
* For that TR with high boost, it would behoove the owner to look for oil that had the highest HTHS rating possible to keep the oil film under these conditions as thick as possible.
*If you live in a region which gets very cold, your daily driver should get an oil with as high a Viscosity Index (VI) as possible to ensure adequate lubrication until warm.
* If you have an engine with flat-tappets, especially a high-performance engine, you need to pay attention to the ZDDP level of the oil. If you decide to use an oil that has low ZDDP, but is otherwise excellent, then you can augment the ZDDP level with ZDDPlus™.
So the answer to Sal’s question is: If you do not have the time to research, buy the best oil you can afford from a brand you trust. Do not sweat the mineral vs. synthetic question. If a no-name oil is extraordinarily cheap, you know that is exactly what it is. If you have the time, read the
ZPlus TechBrief#10 – Oil Base Stocks to educate yourself about the desired properties of oil, then research available formulations and pick the right one.
