184:) up to 200 °C (392 °F) when it is running. The best oils with the highest VI will remain stable and not vary much in viscosity over the temperature range. This provides consistent engine performance within the normal working conditions. Historically, there were two different oil types recommended for usage in different weather conditions. As an example, with winter oils and cold starting the engines, and with temperature ranges from, say, −30 °C to 0 °C, a 5 weight oil would be pumpable at the very low temperatures and the generally cooler engine operating temperatures. However, in hot climates, where temperatures range from 30 °C to 45 °C, a 50 weight oil would be necessary, so it would remain thick enough to hold up an oil film between the moving hot parts.
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oil that cannot be pumped around inside an engine's lubrication system. However, when a spoonful of very cold oil is put into a pan on a stove and it is slowly heated and swirled around, the oil will gradually warm up, and there is a definite temperature range where the oil is warm and traditionally "oily". However, as the oil is heated further, the oil becomes thinner and thinner, until it is nearly smoking and is almost as thin as water – and thus it has almost no capacity to keep moving parts separated, resulting in metal-to-metal contact and damage of the components that are supposed to be kept apart with a thin film of oil.
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137:. The lower the VI, the more the viscosity is affected by changes in temperature. The higher the VI, the more stable the viscosity remains over some temperature range. The VI was originally measured on a scale from 0 to 100; however, advancements in lubrication science have led to the development of oils with much higher VIs.
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The effects of temperature on a single-viscosity oil can be demonstrated by pouring a small amount of vegetable oil into a pot or pan and then either cooling it in a freezer or heating it on a cooking stove. When oils get cold enough in a deep freezer, they will solidify into a block of "wax"-like
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Additionally, there are the issues of oil temperature maintenance, such as oil or engine heaters that enable easy starting and shorter warm-up period in very cold climates, and oil coolers to dump enough heat from the oil, and thus the engine, gearbox, or hydraulic oil circuit, so as to keep the
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Thus the issue of multigrade oils came into being, where with variable temperatures of, say, −10 °C during the cold nights and 20 °C during the days, a 5 weight oil would be good as the oil would be pumpable in a cold engine and as the engine came up to running temperature, and the day
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warmed up, the characteristics of a 30 weight oil would be ideal. Thus the 5W-30 oils were introduced, rather than the fixed and temperature limiting grades – where the thin oils became too thin when hot and the thicker oils became too thick when cold.
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are the viscosities at 40 °C for two hypothetical oils of VI 0 and 100 respectively, having the same viscosity at 100 °C as the oil whose VI we are trying to determine. That is, the two oils with viscosity
466:{\displaystyle {\text{VI}}={\begin{cases}100{\dfrac {L-U}{L-H}}&{\text{if VI}}\leq 100,\\100+{\dfrac {\exp \left({\frac {\log H-\log U}{\log Y}}-1\right)}{0.00715}}&{\text{if VI}}>100,\end{cases}}}
211:(SAE). The temperatures chosen arbitrarily for reference are 100 and 210 °F (38 and 99 °C). The scale was originally interpolated between 0 for a
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applications require the lubricant to perform across a wide range of conditions, for example, automotive lubricants are required to reduce
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and higher-quality base oils are widely used nowadays, which increase the VIs attainable beyond the value of 100. The viscosity index of
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Pennsylvania crude. Since the inception of the scale, better oils have also been produced, leading to VIs greater than 100 (see below).
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in solid body contacts. Generally, the least viscous lubricant which still forces the two moving surfaces apart to achieve "
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Thus the multigrade oils are recommended for use based on the ambient temperature ranges of the season or environment.
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relative to temperature change. It is mostly used to characterize the viscosity-temperature behavior of
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values can be found in tables in ASTM D2270 and are incorporated in online calculators.
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at 100 °C and a VI of 0 and 100 would have at 40 °C the viscosities of
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components when the engine is started from cold (relative to the engine's
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is too viscous, it will require a large amount of energy to move (as in
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is the oil's kinematic viscosity at 100 °C (212 °F), and
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The viscosity index can be calculated using the following formula:
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oil's upper temperature to within a specified upper working limit.
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is the oil's kinematic viscosity at 40 °C (104 °F),
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566:"Don't Ignore Viscosity Index When Selecting a Lubricant"
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527:https://www.lubricants.total.com/what-motor-oil-vi
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522:https://xenum.com/en/engine-oil-viscosity-index/
144:is closely related to its ability to reduce
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47:adding citations to reliable sources
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16:Measure of a fluid's viscosity
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639:"Calculate Viscosity Index"
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541:"Viscosity Index Tables"
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182:operating temperatures
613:"ASTM D2270-10(2016)"
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41:Please help
36:verification
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568:. US: Noria
282:Calculation
670:Lubricants
664:Categories
648:2 February
624:2020-11-29
546:. US: ASTM
517:References
273:Very high
217:paraffinic
213:naphthenic
69:newspapers
680:Tribology
594:29 August
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351:≤
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270:Above 110
262:80 to 110
224:additives
170:lubricant
164:Relevance
154:lubricant
142:lubricant
131:viscosity
572:26 March
550:26 March
254:35 to 80
246:Under 35
176:between
174:friction
146:friction
99:May 2018
435:0.00715
257:Medium
83:scholar
476:where
178:engine
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544:(PDF)
444:if VI
347:if VI
265:High
168:Many
158:honey
90:JSTOR
76:books
650:2021
618:ASTM
596:2018
574:2020
552:2020
509:and
501:and
488:and
448:>
249:Low
121:The
62:news
451:100
411:log
400:log
388:log
374:exp
364:100
354:100
313:100
45:by
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298:VI
127:VI
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337:H
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