Base stocks, an explanation of oil formulations.

[UnleashedBeast]

Many people see the word "Synthetic" on a bottle of oil and assume it's 100% created by man. This is not the case. Base stocks fall into four major categories called groups.

Group II - Petroleum oil, commonly called conventional or dino oils
Group III - hydrocracked, or heavily refined pertroleum, has impurities
Group IV - PAO, man made synthetic, no impurities
Group V - diesters, some polarized, allows engine oil to stick like a magnet to metal

First, let's talk about the difference between group III, IV, and V base stocks, and use a water analogy to see it in simple terms.

Pump water from a lake, river, or stream into a plant. Purify it, remove minerals, and make it look clear. You have "group III" water.

Take Hydrogen and Oxygen in the purest form, chemically bond them together to make "group IV & V" water. With no impurities to remove you have more consistent results and hence....True synthetic!

Group III - Petroleum oil that is pumped out of the ground and refined to be classified as a synthetic base stock, although a lot of experts disagree with this. A few oil manufacturers mostly use group III stocks, but still call it a synthetic...they consider the major changes in the refining process to be "synthesizing" oil. You should also note these oils will never say 100% synthetic on the bottle. The latest refining, and best of these stocks, are called group III+. These stocks seem to be the best at keeping in-solubles in suspension within the oil to carry it to the filter.

Group IV - We call them PAO (Poly-Alpha-Olefin). Like the water analogy they are true synthetic, have better cold pour properties, and better resistant to high heat "torture" situations. These base stocks give longer drain intervals. Non polarized molecules do not stick to metal like a magnetic, that's where esters come into play.

Group V - Esters, the most expensive base stock to formulate. Some esters are polarized and allow oils to stick to metal like a magnet. This helps an engine to avoid dry start ups and reduce wear.

Ok, this is a very basic description of the three primary base stocks. I would also like to add that studies have been taking place and in some cases have seen a group III+ base stock with a good additive pack out perform a group IV stock with an average additive pack, although not in cold weather performance or long drain intervals. This is why oil formulations include a mixture of two or three different base stocks to make an oil work for the intended purpose. Since group III+ and group IV mixtures seem to be common and cheaper to manufacture. Some semi syn blends only contain 10.5% group IV and 89.5% group II (dino oil).

This is why your boutique oils far exceed manufacturers requirements for an oil. They have longer drain intervals, better antiwear agents (better additive addpacks), and why they cost more. Some argue that it's overkill to have an oil to make a car last for 300K miles (dino oils have done this with low OCI), but if I can afford the best, I will buy the best. Companies like Amsoil, Red Line, etc...don't use group III base stocks in their best oils. Amsoil does in their cheaper line oils (oils that are only rated for normal OCI - 7,500 miles). The true advantage of high end oil is longer OCI, less money investment overall, less wear versus miles run on the same oil, and less work with less oil change intervals.

I know this was vague, but the information is so in depth and technical sometimes it even has me reading it again to better understand it.

Now, how does this apply to what you commonly find at the auto parts store or Wal Mart? Let's roll the clock back to the 1990's.

Castrol began using group III base stocks in their synthetic line of engine oils. Mobil 1 decided it wasn't fair and misleading to customers so they sued Castrol in court. You read above about the process of hydrocracked petroleum, and the courts agreed with Castrol that this process was enough to consider the base stock "synthetic". This promoted other oil manufacturers to follow lead and reduce costs of production (group III is cheaper to manufacture than group IV and V), so they too began using group III.


Let's advance some years later...about the time of hurricane Katrina. After the destruction in the gulf, Exxon Mobile had a short supply of what was needed to manufacture group IV (PAO) base stocks. So they did this...

PAO is very short in the whole industry, still. Lots of suppliers are reformulating on the fly, partially substituting Grp III & boosting the AO to compensate.

and to justify their actions they said...

"Probably 95% of the cars & light trucks on the road will see no difference in engine life between a synthetic & a good quality mineral. Lots of high-end cars are specifying synthetics, but that has more to do with their desire to present a certain cachet to the market rather than the actual lubrication requirements of the engine in question."

but left out two important facts...

1. European manufacturers demand long OCI (15,000 miles) to avoid more waste oils and help the environment. If they can get you to change your oil more, they make more money....simple math. Who do you think began the 3,000 miles or 3 months oil change intervals? Of course, the manufacturers did, even though they had synthetics that could do 5 times that interval.

2. They didn't tell you they were making the oil with cheaper base stocks, and wanted you to believe they were still group IV/V blends. All the while, the prices went up or stayed the same. What's that tell you about their bottom line profit?

Now, let's talk briefly about API standards, and how it is effecting engine oil protection. Current SM testing only allows a certain level of Zinc and Phosphorus levels in engine oils (due to happiness of tree huggers and catalytic converters). SM decreased these levels versus SL standards. You may notice that the best oils from AMSOIL are NOT API certified, and here is why.

AMSOIL (and others) doesn't agree with API standards of reducing these valuable additives as they are important to protect an engine from wear. They will not reduce current zinc and phosphorous levels in their current formulations to meet newer SM standards. AMSOIL feels there are other factors involved that API is not taking into consideration. This is one of the reasons why AMSOIL protects your engine from wear better than the rest. When other factors are taken into consideration the levels AMSOIL chooses that meets older standards will be sufficient under new standards.

So, I hope that this has been helpful to understanding base stocks, formulations, and the way your common over the counter engine oil manufacturers want to take advantage of you, and your wallet.