Oil must be capable of flowing at low temperatures, so that it gets around the engine in a fraction of a second at start-up and must protect engine components at high temperatures without evaporating or carbonising and maintain adequate oil pressure. This is called “hydrodynamic lubrication” and crank bearings depend on it. Oils work because they have viscosity the drag of a rotating part pulls oil from a low-pressure area into a high pressure area and “floats” the surfaces apart. Viscosity is the force required to shear (break) the oil at a certain speed and temperature. Viscosity is the most misunderstood aspect of oil and yet it is the most important. Shop For Motorcycle 2 Stroke Engine Oil / 4 Stroke Engine Oil Oil Viscosity / Grade Find out exactly what it all means and cut through all of the misinformation and myths and read some REAL facts. There are so many people that simply don't understand viscosity / grade in the automotive trade that it's worrying, that's why we have the information below. Lubricants are becoming ever thinner to meet modern engine requirements and no doubt will look very different in 10 years time.Engine Oil Grade / Viscosity Explained Find out exactly what grades are, and what the W really stands for, plus much much more SAE J300 is a constantly evolving document considering advances in testing and technology. Included at the end of this document is a SAE J300 table, containing all of the limits for engine oil viscosities. It’s worth noting these figures do not relate to any kind of performance and indeed an engine oil with no additives can be an SAE 15W-40. SAE 40 tells us the oil has a viscosity at 100☌ between 12.5 – 16.3 and an HTHS viscosity above 3.7. This means oil will flow lubricating the engine on initial start-up in climates where a 15W oil has been recommended by the OEM (Original Engine Manufacturer). It has low temperature properties, denoted as 15W (W referred to as Winter)ġ5 tells us the oil has been tested at -20☌ for cold cranking viscosity and -25☌ for pumpability.It’s a multigrade oil quoting both high and low temperature limits.If we look at a typical viscosity grade such as 15W-40 it can be broken down as follows: A typical OEM would produce a document list of lubricant possibilities such as the following for a specific engine:Įxample: Understanding the Current Classification System Everything from 0W-8 to 25W-60, meaning that OEM’s have a list of possibilities to ensure that not only does the engine oil perform in ‘moderate’ temperature climates, but also in Artic and Desert terrains. If written down, the possible combinations of multigrade engine would form a very large list. Monograde engine oils are still defined by SAE J300 but only the lower half of the table applies. With monograde oils there is no requirement for cold temperature testing and therefore there is not W number stated. These oils find application in many areas, from Vintage and Classic engines to lawn mowers and gearboxes. Monograde engine oils are only denoted by a single number, i.e. SAE J300 is constantly evolving with additional viscosity grades and there’s no doubt that the future will introduce increasingly refined classification systems. In 1992, High Temperature High Shear (HTHS) finally found its way into the chart as a more accurate measure of the conditions and temperatures found within engines. During the eighties’ in the US, the now infamous Winters in Sioux falls tested the classification system leading to improvements within the measurement of cold temperatures, particularly the cooling rates and the formation of waxes. In 1972 the system became metric using Celsius and viscosity measurements in cSt with the addition of a pumpability test in 1978, due to concerns over solidification and nil flow when cold. As with all systems the classification system evolved and by 1959 it became known as ‘SAE J300′.īy 1967, it was evident that the classification method was too simple and Cold Cranking viscosity was introduced to monitor viscosity at low temperatures. This classification was used to denote a 10, 20, 30, 40 and therefore was the forerunner of todays classification systems. The first known tables for viscosity classification were available in 1911, categorised with a series of numbers determined by the oils flow time through a cup. Classifying different types of oil has always existed, either in terms of performance or viscosity.Ī Brief History of the Classification System Motor oils as we know them today have evolved considerably since their first inception over 100 years ago.
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