Volume 1 Issue 3 - Lubrication

Synthetic Oil Classifications

I said it would be a brief explanation of crude oil refining and I stuck to my word. Now it’s time to give a brief explanation of synthetic base oils and then take a look at the quality groupings. Again, this very brief fundamental understanding of the differences in petroleum and synthetic oils will serve you well in any and all discussions on finished oil products.

Synthetics have historically been defined as oils that synthesize light weight molecules to form heavy weight lubricating molecules. This definition is certainly true, but some variation has been allowed to include modifying the original molecular structure. The chemists are continually perfecting the design and production of various synthetic molecules, but the goal is always to produce the best design for the intended application. You can see this in the origin of synthetic oils by Standard Oil in the 1930s. These first synthetics were intended specifically for problematic lubrication applications. It was not until World War II, when the Germans found themselves with little petroleum that large scale production of synthetic lubricating oils began. By the end of the war the advent of jet engines required the first true large scale practical application of synthetic oils. Jet engines require oils capable of lubricating at minus 50ºF and up to 400ºF, a task simply beyond any petroleum oil parameters.

Synthetics come in several different chemical compounds. I will only address those used for automotive and truck applications (there are several for industrial and specialty applications). Alkylated Aromatics, Esters, Polyalphaolefins (PAO) and Hydrocracked Petroleum make up the vast majority of synthetics used in auto and truck applications, so let’s take a brief look at each.

Alkylated Aromatics

These are synthetic hydrocarbons that are compatible with mineral oils and used for industrial applications such as compressor and hydraulic oils.

Esters

I have purposely grouped the esters for simplification and am only addressing the common characteristics, not the separate individual properties. Esters have very high viscosity index (VI) ratings and excellent low temperature fluidity. Additionally, esters have good lubricating properties and excellent thermal and oxidation stability. One double edged sword for esters is the exceptional solvency and detergency that makes them super cleaning agents. It is important to recognize the cleaning capabilities of esters and use them prudently. Esters can be manufactured in a variety of geometric shapes and molecular structures and it is critical to use the correct esters for the intended application. Esters are not uniformly compatible with all seals, paints or varnish finishes.

Polyalphaolefins (PAO)

PAOs are synthetic hydrocarbons that are compatible with mineral oils; they exhibit a very high viscosity index and very low temperature fluidity. PAOs are used in virtually every sector of lubrication from automotive to industrial. PAOs are compatible with seals and paints in the same way that mineral oils are compatible. Esters are blended with PAOs for superior base oils for high temperature gear and bearing oils.

Hydrocracked (Synthetic)

These are natural hydrocarbons processed by hydro-treating/hydro-cracking to produce a pure base oil, absent of any impurities. This process de-polarizes and modifies the natural petroleum and thus qualifies the oil as synthetic by virtue of the molecular modifications.

So there is my brief description of synthetic base oils. All oils, both mineral and synthetic are placed in groups to indicate the classification (Table A).

API BASE OIL CLASSIFICATION GROUPS (Table A)

As you can see in Table A, the groups are based on oil purity and viscosity index. Saturates relates to the oxidation stability of the oil and Sulfur represents the percent of sulfur in solution. Although PAOs only have to be greater than 120 for viscosity index, 135 is common. Esters will usually have a viscosity index of greater than 140 and both esters and PAOs are free of sulfur. Oil base stock quality is based on many factors in addition to the classifications listed in this table, but the groupings in this table are referred to throughout the industry. For instance, hydrocracked synthetic is typically referred to as a Group III synthetic whereas PAOs are referred to as Group IV synthetic.

Summary

So, in this and the previous two installments of Lube Notes, we have looked at:

• What lubricating oils accomplish in their various applications
• The functions of the different additives that are combined with base stocks in order to meet the requirements of the intended applications
• The origin of petroleum base stocks and their composition contrasted to synthetic lubricating oils

Next time, we will mix up a quart of oil in order to better understand how combining base stocks and additives affects the finished product as well as what the need for additives reveals about a given product’s quality.

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Paul said:

Just a DIY person because of necessity I always used Havoline oil straight 30 weight year round and always had a clean engine that was not excessive oil user most times maybe half quart between 3000 mile changes. It stayed reasonably clear and kept engine really clean inside. What changes made them go to a discolored oil that didn't look clean very long. I drove chevy pickups with the 4"56 rear end at high rpm (no problems), 57 pontiacs, 56 buick, 59 pontiac, and other various cars and always used the Havoline with clean engines and no issues. I don't know which oil is best but in 2006 uplander we only use valvoline 5-20 and no isssues but oil doesn't stay as clear as long as the clear Havoline did. I had a valve job done on my 64 3/4 ton chevy 230 six with about 200,000 miles and the shop asked how I got the head so clean ,I told him the oil I used was Havoline and changed about 3000 miles or so. First time head or engine was apart because it overheated extremely hot that the accumulated hard oil and dirt was running down side of engine. Head was surfaced .030 and new intakes were put in and engine didn't use oil for another 50,000 or more miles when I traded it off. It was a 230 cu. inch engine 4speed truck with the 4:56 gears and drove frequently at 65 mph with the little engine turning high rpms and staying together and never been torn down till got hot and only head work done. Wish I had it back even with the 16-18 mpg. Wow maybe more than just a comment. I am 68. I have tried some synthetics but not enough to evaluate.

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October 08, 2012
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