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Man kör ett antal standardiserade tester uppsatta av:
American Soc. of Testing Materials
The ASTM, quite simply, is an organization whose primary purpose is to assist in the development of international standards for innumerable processes utilized within countless different industries.
With regards to motor oils and lubricants, the most common place that you will run into references to ASTM will be in regards to test methods utilized to generate technical specifications for the motor oils you might be considering. In most cases, when you look at the technical data sheet for a motor oil, you will find that the vast majority of the tests that were run on the oil should have an ASTM test method number listed next to the test results.
If you do not see an ASTM test method number, you have no way to guarantee that the company has used a standardized test method. Without this guarantee, you have no way to be sure you're making an apples to apples comparison of technical specifications between two different oils.
However, if two different oil companies list test results on their data sheet, and both companies reference the ASTM test method number (along with any pertinent test method parameters), then you can have confidence that you are making an apples to apples comparison of the numbers.
Having ASTM test method standards is an invaluable tool in being able to not only categorize and certify motor oils, but also in the process of comparing various motor oils to determine which oil serves your needs best. Look for the ASTM test method number for guaranteed repeatability and validity of test results.
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Kinematic Viscosity @ 40° C
Although this test is not used specifically for classification of the oil as a certain viscosity, it is used for establishing the Viscosity Index of the oil. In laymen's terms, it represents how "fluid" the oil is at 40 degrees C.
Kinematic Viscosity @ 100° C
Similar to above, this represents how "fluid" an oil is at 100 degrees C. Used for establishing the SAE viscosity classification of the oil and for determining it's Viscosity Index. Neither higher, nor lower is necessarily better. Depends upon the circumstances.
Viscosity Index (VI)
An oil's VI rating refers to its ability to maintain a consistent viscosity over a wide temperature range. The higher the VI, the better this ability to maintain consistent viscosity. One thing to keep in mind regarding VI numbers is that they only refer to an oil's ability to maintain consistent viscosity when new. They tell you nothing about how quickly the oil will lose this ability to maintain its viscosity over time.
Premium synthetics need VERY LITTLE VI improver additives (explained in The Motor Oil Bible) to maintain their viscosity over wide temperature swings because their basestocks are much more stable. Typically, the VI improver additives used in these premium oils are more stable as well, allowing them to maintain their effectiveness for long periods of time.
Petroleum oils need considerable VI improver additives to raise their viscosity index and often use low quality additives that are very prone to shearing, reducing their effectiveness over time.
Cold Crank Simulator (CCS)
The Cold Crank Simulator measures the "startability" of an oil by measuring the speed at which a shaft can turn within an oil that is cooled to a certain temperature. In order for an oil to be classified as a multi-grade (multi-viscosity) oil, it must achieve a certain "score" on the CCS test as described in the SAE J300 Physical Requirements for Engine Oils specification.
When reading CCS numbers be careful not to assume that the score is a measurement of the speed of rotation of the shaft. If it was, a higher number would be better. This is not the case. You want a low score on the CCS test. The lower the score, the better the oil performs in cold temperatures.
Pour Point (PP)
Another test designed to establish cold weather performance of an oil. In simple terms, the pour point is the lowest temperature at which an oil will actually flow. This does not mean that it would easily pump through an engine at this temperature - just that the oil still acts somewhat like a liquid at this temperature. Lower is better.
Keep in mind that in oils where pour point depressants are necessary (generally, petroleum oils and low grade Group III synthetics), the pour point of the oil will rise slightly every time your oil sees cold temperature weather. This is because those pour point depressant additives will become less effective over time.
Synthetic oils do not use pour point depressants (or will at least use VERY little), so they will hold a consistent pour point for a much longer period of time.
The pour point listed on a spec sheet (and on my charts) is for a NEW oil. It tells you nothing about how long an oil will maintain this cold weather performance. Oils which contain alot of pour point depressants will lose cold temperature performance very quickly.
Flash Point (FP)
The flash point of an oil is the temperature at which the oil vaporizes enough for the gas to become momentarily flammable in the presence of a small flame. There are other conditions and requirements for this test, but the gist of it is that an oil reaches its flash point when it begins to significantly vaporize.
Higher is better. In today's modern engines a flash point under 400 degrees F is unacceptable. Look for an oil with a flash point of at least 420 degrees F if you want the good stuff. a good quality synthetic or parafinic base petroleum oil will often be significantly higher than this.
Total Base Number (TBN)
Basically, the TBN of an oil is a relative indication of how well it can neutralize acid build-up within an oil and for how long it can do it. The higher the number the better equipped an oil is to neutralize acids from condensation, oxidation processes and combustion by-products.
Generally, gasoline oils will have TBN values of 5 to 8 and diesel oils will have TBN values around 9 to 14. Higher is better.
High-Temperature/High-Shear (HTHS)
This test is a simulation of the shearing effects that would occur within an engine. In fact, it's actually designed to test motor oil viscosity in operating crankshaft bearings and simulates motor oil stress at temperature extremes.
Higher is better as this means that the oil maintains it's viscosity under shearing stress and temperature extremes. Oils with a low HT/HS score will not maintain high viscosity index for long. So, if an oil's VI is high, make sure it's HT/HS is also high, indicating that the VI will STAY high.
Since this test is used to determine an oil's viscosity classification, it should be provided on a spec sheet.
Noack Volatility Test
The NOACK Volatility Test is one that is becoming more common on motor oil tech sheets, but still is not always provided. However, in my opinion, it is one of the most important technical specifications you can look at to determine the quality of an oil.
In addition, since this test MUST be run for API classification, the oil manufacturer HAS the data. There's no reason to leave it off a spec sheet unless it's to hide the spec from potential customers.
The NOACK test exposes an oil to a high temperature environment of 250 degrees C (almost 500 degrees F) for one hour. Other standardized environmental conditions are also set to make sure that the test is always performed in the same manner. The test is designed to determine the amount of evaporation that will occur over the course of this one hour time period.
The final score is listed as a percentage of weight loss by the end of the test and less weight loss is better. Thus, a lower NOACK score is better.
Och detta är bara en del...
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/Thomas