Oil Viscosity Chart

oil viscosity chart

Oil 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.SAE used viscosity to classify motor oils in different categories.

I will personally recommend to watch this video to get answers on oil viscosity chart

SAE Oil viscosity chart

We have to understand viscosity in order to understand oil viscosity chart.SAE developed a standard system to assign numbers to motor oils based on viscosities 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 temprature

Viscosity 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 Viscosity

Dynamic viscosity is determined by measuring shear stress.Unit of measuring dynamic viscosity is centipoise (cP).

2)Kinematic Viscosity

It 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 is centistoke (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.

Points to remember

Viscocity is inversely proportional to temprature.

Viscocity is directly proportional to pressure

The viscosity of oil decreases when it is heated.

oil viscosity of Single grade oil is shown below

0W
5 w
10 w
15 w
20 w
25 w
20
30
40
50
60

First six grades are known as winter grades.These six grades have W attached to their number.W means that the viscosity of oil is tested at low temprature.

Dynamic viscosity of winter grade is calculated using

Cold Cranking Simulator
the Mini-Rotary Viscometer

Oil is given one of 6 winter grades Based on the coldest temprature at which it passes.For single non winter oils,viscosity is measured at 100 degree celsius or 212 degree farenhite.Based on time taken by oil to flow,it is graded as one of these SAE viscosity numbers 20, 30, 40, 50, or 60.

These single grade oil is suited for classic cars or lawn mowers where the operating temperature difference does not vary much.

You must buy motor oil of the grade as specified by your manufacturer.

Oil viscosity chart of Multi grade oils

Multi grade oil is one whose viscosity does not vary much by temperature differences.VII (viscosity index improvers) are added to bring the difference in viscosities closer together.

10 W-30 is multi-viscosity or all weather oil.10 W-30 means that it meets viscosity requirements as specified by SAE in the temprature range 10 degree farenhite to 30 degree farenhite.

What is The importance of learning sae oil viscosity

I think my readers can answer this question comfortably.It helps you to buy perfect motor oil based on your car and climate.In simple words it is an attempt to grade the motor oil taking your climate and its viscosity in consideration.

Below you can see image of sae oil viscosity chart

It explains sae number of both sigle grade and multi grade oil.

API (american petroleum instute) also provides temprature viscosity relationship of oils.Their numbers are slightly different from SAE numbers or grades.

American petroleum institute provides below oil ratings :

Another sytem of oil viscosity relationship is ISO.ISO grades viscosity of oils at 40 and 100 degree celcius.

ISO Oil chart

ISO VG Grade	Midpoint Viscosity 40 degree celcius/cST	Minimum Viscosity @ 40 degree celcius/cST	Maximum Viscosity @ 40 degree celcius/cST	SAE Viscosity Grade	Minimum Viscosity @ 100 degree celcius/cST	Maximum Viscosity @ 100 degree celcius/cST
15	15.0	13.5	16.5
22	22.0	19.8	24.2
32	32.0	28.8	35.2
46	46.0	41.4	50.6
68	68.0	61.2	74.8	20	5.6	9.3
100	100.0	90.0	110.0	30	9.3	12.5
150	150.0	135.0	165.0	40	12.5	16.3
220	220.0	198.0	242.0	50	16.3	21.9
320	320.0	288.0	352.0
460	460.0	414.0	506.0
680	680.0	612.0	748.0

Oil viscosity explained with the help of videos

Oil viscosity technical information

Motor oil viscosity

Viscosity temprature relationship

I hope that you have understood Oil viscosity chart completely after going through my article,tables and hand picked videos.