What Is 20 or 30 Weight Detergent Motor Oil?
The oil penetrates bearings and moving parts inside an automotive engine to provide lubrication and shear protection. Detergent motor oils with SAE grades 20 and 30 are typically used in older automobile engines with lower temperature and pressure ranges. Modern passenger vehicle engines primarily use multiple-grade oils. Some modern racing engines, two- and four-stroke small engines and industrial engines specify single-grade oil.
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SAE Grading
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The SAE 20 and SAE 30 grading is provided by the Society of Automotive Engineers, or SAE. Tests are conducted on oil samples to determine the viscosity, or relative thinness, of the oil at specific temperature ranges. The SAE Grading measure the amount of time the oil takes to pour through a hole in a viscometer. Five seconds results in a grade of 5, 20 seconds a grade of 20, and 30 seconds a grade of 30. The relative thinness of the oil changes how fast the oil pours through the hole. SAE 20 oil pours 50 percent faster through the viscometer than SAE 30 oil at the measured temperature. The SAE grading is commonly referred to as the "weight" of an oil, though relative weight is not directly correlated to the grading system.
Detergent Oils
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Modern oils include detergents to carry away particles that would otherwise settle in and on engine parts. Detergent oils wash away the particles to keep the engine clean of sludge. Overheating motor oil breaks down the molecular chains and degrades the ability of the oil to act as a detergent.
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Oil Changes
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Detergents also have a limited life span, requiring the oil to be periodically changed. Particle suspension also can reach a saturation point that requires a change of oil. Follow the vehicle engine manufacturer's recommended guidelines for oil change intervals.
Recommended Temperature Ranges
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The viscosity of oil not only determines how well it protects against shear and high pressure conditions, it also determines how easily it pours in cold conditions. As oil gets colder, it thickens until it can no longer pour effectively. The "pour point" is specified as 5 degrees Centigrade warmer than chilled oil that does not pour. SAE 20 grade oil pours down to minus-5 degrees Centigrade, whereas SAE 30 grade oil pours to 0 degrees Centigrade. Non-detergent oils will pour at lower temperatures. Many brands of oil exceed the pour point specifications and pour at significantly lower temperatures. Consult the manufacturer of the oil to determine the specific pour point.
Use of Low Viscosity Oils
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The SAE 20 grade oil's lower viscosity classifies it as a "low viscosity oil." The SAE 30 grade oil's relatively higher viscosity classifies it for higher operating temperatures and pressures. Engine bearing clearances require a certain amount of viscosity to function properly. Use of a lower than recommended viscosity may reduce friction and improve mileage, but also will reduce the lifespan of the parts. Use the recommended SAE grade oil in the vehicle's engine to avoid premature damage to sensitive parts.
Multiple Grade Oils
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Multiple grade oils, such as 10W30 or 5W20, indicate that the oil performs like a lower viscosity oil in cold temperatures. The "W" refers to "winter," meaning the first rating applies to cold viscosity. The second rating indicates the viscosity of the oil at normal operating temperatures. For example, a 10W30 oil has a viscosity rating of SAE 10 in cold temperatures and SAE 30 at normal temperatures. The multiple grades are achieved by replacing some of the base stock with viscosity modifiers. Most modern passenger vehicles specify multiple-grade oil to ensure protection during a variety of climate conditions. Racing engines, performance engines and engines designed to operate in warmer temperatures may specify single-grade oils.
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