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Car & Motorbike Engine / Gear Oil Base Stocks Explained

Find out what goes in to a engine / gear oil

Base stocks are the very core of a automotive oil, and they make up a massive part of the finished lubricant, find out all about why you should be bothered about right here

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Base stock Categories and Descriptions

All oils are comprised of base stocks and additives. Base stocks make up the majority of the finished product and represent between 75-95%

Not all base stocks are derived from petroleum, in fact the better quality ones are synthetics made in laboratories by chemists specifically designed for the application for which they are intended

Base stocks are classified in 5 Groups as follows:

Group 1

These are derived from petroleum and are the least refined. These are used in a small amount of automotive oils where the applications are not demanding

Group 2

These are derived from petroleum and are mainly used in mineral automotive oils. Their performance is acceptable with regards to wear, thermal stability and oxidation stability but not so good at lower temperature

Group 3

These are derived from petroleum but are the most refined of the mineral oil base stocks. They are not chemically engineered like synthetics but offer the highest level of performance of all the petroleum base stocks. They are also known as “hydrocracked” or “molecularly modified” base stocks

They are usually labelled / marketed as synthetic or semi-synthetic oils and make up a very high percentage of the oils retailed today

Group 4

These are polyalphaolefins known as PAO and are chemically manufactured rather than being dug out of the ground. These base stocks have excellent stability in both hot and cold temperatures and give superior protection due to their uniform molecules

Group 5

These special base stocks are also chemically engineered but are not PAO

The main types used in automotive oils are diesters and polyolesters. Like the group IV base stocks they have uniform molecules and give superior performance and protection over petroleum base stocks. These special stocks are used in all aviation engines due to their stability and durability. Esters are also polar (electro statically attracted to metal surfaces) which has great benefits. They are usually blended with Group IV stocks rather than being used exclusively.

It is common practice for oil companies to blend different base stocks to achieve a certain specification, performance or cost. The blending of group IV and V produces lubricants with the best overall performance which cannot be matched by any of the petroleum basestock groups. overall performance which cannot be matched by any of the petroleum basestock groups.