oil 9 whai is the meaning of " m ultigrade"
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when applied to an engine lubricating I have been told that viscosity of a multigrade oil is constant at all temperatures. Is this correct?
AAlthough a multigrade oil is said to have a constant-viscosity characteristic, its viscosity is, in fact, reduced with an increase in temperature. The loss of viscosity is, however, relatively small compared with other grades.
Take the case of an SAE 10W/30 multigrade oil. The classification 10W indicates that the oil has a viscosity equal to that of an SAE lOW lubricant at a temperature of Odeg F and a viscosity of an SAE 30 oil at 210deg F. The W in 10W, 20W or 30W classification shows the rating of the oil at Odeg F in every case and that the lubricant is suitable for starting in cold climates. SAE 20, 30, 40 and 50 cover viscosities at the higher temperatures and indicate that the oil is suitable for operation in hot climates. While the main additive of a multigrade oil is a viscosityindex improver, oils of this grade are treated with other additives in addition to a VI type. These include detergent/dispersant and anti-oxidant additives.