What are the important things to consider when making a motor oil comparison? While some may prefer to solicit the opinions of others (anecdotal evidence), the fact is that it is best to look at technical specifications when comparing oils. This will allow you to choose an oil that best suits your needs.
Technical specifications for motor oils can generally be found on the particular brand’s website, although sometimes it may be necessary to contact the company to ask that they provide them. Each specification is found using a standardized testing method (ASTM-American Society of Testing and Materials) and is assigned a certain test number. There are around 16 specifications you might see on the data sheet for any given oil, although it’s more likely you will find around 8 or 9. Which are most important?
There are around 11 tests which are of varying importance. Below is a brief description of each and why it is important:
• Viscosity Index-tests the ability of the oil to maintain viscosity over a wide temperature range (the higher the number, the better the ability);
• Cold Crank Simulator-tests the speed at which a shaft can turn within an oil that is cooled to a certain temperature;
• Mini-Rotary Viscometer-tests the pumpability of the oil-how easily will the oil flow through the engine;
• Pour Point-tests for the lowest temperature at which an oil will actually flow;
• Borderline Pumping Temperature-tests for the lowest temperature at which the oil will adequately flow through your engine;
• Flash Point-tests for the temperature at which the oil vaporizes enough for the gas to become momentarily flammable (the point at which the oil vaporizes);
• Fire Point-tests for the point at which an oil gives off enough vapor to provide a continuous flame;
• Total Base Number-tests for an indication of how well an oil can neutralize acid build-up and for how long it can do it;
• High Temperature/High Shear-this test simulates motor oil viscosity in operating crankshaft bearings;
• Noack Volatility Test-test that determines the amount of evaporation that will occur over the course of this one hour time period;
• Four Ball Wear Test-test that establishes how well a lubricant will prevent wear in situations where there is sliding contact going on;
By no means is this list comprehensive. There are other tests which companies use in addition to those listed here. Nevertheless, which of these tests are most important? The author of The Motor Oil Bible points to three: the Noack test, the Four Ball Wear Test and the HT/HS test. Why these three? All of these tests are designed to simulate conditions that would be found within at least a portion of your engine during use.