Oil Viscosity Chart -- for automobile driversOil viscosity chart is must for all automobile drivers.This article is an attempt to explain oil viscosity chart to beginners.Viscosity is single most important factor to judge oil quality at different tempratures.So SAE used viscosity to classify motor oils in different categories.

SAE and Oil viscosity chartWe have to understand viscosity in order to understand oil viscosity chart.SAE developed a standard system to assign numbers to motor oils based onviscosities of Oil at different temperatures.SAE(Society of automotive enginners) measures the viscosity of oil in temperature range of 0 degree farenhite to 210 degree farenhite.Oils that meet SAE's viscosity requirements at low tempratures have a W after the viscosity rating (for example 20 W).Oil that meet the viscosity requirements at high temperatures are simply numbers (for example SAE 40).Your engine needs low rated Oil for cold start and high rated oil when engine is hot.

Viscosity and tempratureViscosity is inversely propportional to fluidity.The less viscous fluid will flow easily compared to high viscous fluids.For example water has less Viscosity than honey.Hence water will flow smoothly in comparison to honey.You can think of Viscosity as fluid's resistance to flow.Viscosity is dependent on temperature.A temperature change will cause the viscosity of the fluid to increase or decrease.

Viscosity can be measured as :1)Dynamic ViscosityDynamic viscosity is determined by measuring shear stress .Unit of measuring dynamic viscosity is centipoise (cP).2)Kinematic ViscosityIt is more popular method.It is calculated based on the time taken by oil heated at specified temperature to flow through a hole of specified size.A capillary is used to provide accurate measurement.Unit of measuring kinematic viscosity iscentistoke (cSt).Oil which is high in viscosity will take more time to flow out of hole.Oil high in viscosity are known as thick oil and oil low in viscosity is known as thin oil.