These additives reduce oxygen attack or oxidation of the oil, helping to reduce oil thickening, especially at consistently high temperatures experienced over the life of the oil drain period.

All modern lubricants being hydrocarbon based, are susceptible to oxidation. Each type of base oil (mineral or synthetic) has a stable threshold beyond which stabilizers or oxidation inhibitors are needed to retard oxidation.

The process of oxidation occurs in three stages.

Stage 1 - Lubricant and fuel react with oxygen to form radicals.

Stage 2 - Radicals react with oxygen and the lubricant to form hydroperoxides.

Stage 3 - The hydroperoxides decompose to form a variety of additional radicals

The result is, carboxylic acids attack iron metal and copper and lead bearings to form metal carboxylates, which further enhance the rate of oxidation.

An increase in temperature affects the oxidation process, with the rates of oxidation approximately doubling with every 10‑degree rise in temperature. High operating temperature and high air exposure applications require a high level of oxidation protection.

Oxidation can be caused by –

• Worn metals can enhance the rate of oxidation
• Glycol contamination
• Thermal degradation
• Severe soot contamination

If this process is not controlled, the lubricant decomposition will lead to oil thickening, sludge formation, and the formation of varnish, resin, and corrosive acids.

Engine oil and other driveline lubricants are made up of a composition of base oils + additives.

Blended lubricants contain base oils mixed with additives to form a specific oil for an intended application. Whether this be an engine oil, gear oil or automatic transmission fluid, will determine the blend and what ingredients will go into the mixture. Base oils and additives are also used in semi solid lubricants such as greases.

Different types of oils require different percentages of additive package depending on viscosity grade, specification, oil type etc. The base oil will also vary depending on the application or specification required. A typical break down of ingredients could look as follows -  

To create a blended lubricant, firstly you have base oils, made from either a crude derived base stock, man-made synthetic or a blend of these base oils.  To achieve the functions required by finished lubricants, you must then put additives in with the oil. These all do different things. Some of the additives used in oils are -

• Detergents
• Dispersants
• Viscosity Index Improvers
• Pour Point Depressants
• Foam Depressants / Air Release Agents
• Anti-Wear Additives
• Oxidation Inhibitors
• Friction Modifiers
• Extreme Pressure Additives
• Rust and corrosion Inhibitors

A typical break up of an engine oil additive pack, could be as follows -

Depending on the oil type and specification, the performance pack will alter significantly.

Detergents are usually metallic compounds and they control deposits and keep engines clean. They are polar in nature, which allows them to cling to the surfaces of particles.

1. They lift any deposits from the surfaces of the engine to which they adhere to and then chemically combine to form a barrier film, which keeps the deposits from coming out of suspension and coagulating.
2. Detergents neutralize any acids formed by the combustion of the fuel by chemically reacting with the acids in order to form harmless neutralized chemicals.

Any oil with an API engine rating of SC, or above has a level of detergency. Later specification oils generally tend to have a higher detergency than older specification grades.

The number of particles that can be contained by the detergents is limited. When the number of particles exceed the capacity of the type of detergent chemistry being used, deposits can form. Therefore it is necessary that the engine oil be drained before this happens if engine cleanliness is to be maintained.

These are usually ashless (non metallic) organic chemicals. They keep contaminants and by-products dispersed in the oil helping to prevent deposits and sludge from forming. Dispersants form a "Micelle" enveloping particles and keep them finely divided. These micelles can trap deposit precursors up to 0.05 microns in size. They can keep contaminants that are so fine in suspension, they pass through the oil filter with the oil.

Their functions in engine oil are to -

1. Suspend particulate contaminants in the oil
2. Minimize & prevent sludge formation
3. Suspend oil‑insoluble resinous oxidation products
4. Prevent particulate‑related abrasive wear
5. Prevent viscosity increase
6. Stop oxidation‑related deposit formation.

Dispersants are primarily used in gasoline engine and heavy duty diesel engine oils, which account for 75 to 80% of their total use. They’re also used in natural gas engine oils, aviation piston engine oils, automatic transmission fluids and some types of gear lubricants.

Used to reduce internal engine friction and are common in low viscosity oils where fuel economy is important. They affect the frictional properties between two rubbing surfaces to prevent scoring, reduce wear and noise.

They are commonly used in gasoline engine oils, and are added to fluids for automatic and manual transmissions, tractor hydraulic systems, power steering, shock absorbers, and metal working applications. In automatic transmission fluids and limited-slip axle lubricants, friction modifiers control torque application through clutch and band engagements.

Friction modifiers can compete with anti-wear agents at high temperatures and with corrosion and rust inhibitors at low temperatures.

Anti-Wear Agents prevent wear from seizure or scuffing of metal surfaces that would otherwise rub or contact each other. They are normally zinc and phosphorus or other organo-metallic based compounds such as boron, and are sacrificial, decreasing throughout the oil drain interval.

In addition to providing anti-wear protection, zinc dialkyl dithiophosphates (ZDDP) act as oxidation and corrosion inhibitors. They are primarily used in gasoline and diesel engine oils as well as  in industrial lubricants.

Zinc is a polar molecule, so it is attracted to steel surfaces. Under heat and load, the Zinc reacts with the steel surface and creates a phosphate glass film that protects the steel surface by forming a sacrificial film that covers the peaks and fills in the valleys of the steel surface. Other additives like detergents, dispersants, viscosity index improvers, and others all compete against the Zinc inside the engine – sometimes with negative consequences. Calcium-based detergents and dispersants compete against the ZDDP for surface space. Detergents and dispersants see Zinc as another contaminant in the engine and hence try and clean it up!

So the balance of additives is critical to the performance of the oil to be able complete its desired function.

ZDDP works because it is a polar molecule, so it is attracted to ferrous metal surfaces. However, zinc is not a protectant until heat and load are applied. ZDDP must react with heat and load to create the sacrificial film that allows zinc to protect highly loaded engine parts.

In addition to zinc, other anti wear agents such as Boron and PTFE are used in oils as sacrificial agents. Boron offers much greater protection than even Zinc by increasing the load carrying capacity of the oil by as much as 8 times in a 4 ball load test. It also showed a 12.5% decrease in scarring over a normal engine oil with a standard anti-wear additive pack and better than 50% less scarring than a base oil only 4 ball wear test. Apart from it's increased protection, boron does not increase emmision levels and is safe for catalysts.

ZDDP (Dialkyl Dithiophosphate), is a chemical compound used in engine oil as a sacrificial and very effective anti-wear agent. There has been a big focus on zinc, also known as ZDDP or ZDTP (zinc dithiophosphate). For many years this has been the anti-wear additive of choice for many engine oils as it is the most cost effective (and one of the most effective) chemistries to use.  It is sometimes incorrectly described as an extreme pressure additive with its primary role being a sacrificial anti wear agent to prevent wear in the rings and in the valve train (cams, tappets, valve stems etc) of the engine.

History

ZDDP was developed in the 1940’s initially as a bearing corrosion inhibitor before being used as a sacrificial anti wear agent for engine oils. From the early 1920’s to the mid 1980’s petrol contained tetraethyl lead which contributed to the build up of lead & lead oxides in the engine. Lead scavengers were then introduced but these caused acidic by products in the crankcase that reduced the effectiveness of the ZDDP. To counteract this, higher ZDDP dosages were introduced often into the range of 0.14 - 0.16%. The increase also pushed up levels of Phosphorus which is part of the ZDDP compound along with zinc.

The introduction of the USA Clean Air Act in 1975 required a 75% decrease in emissions in all new model vehicles after 1975, a decrease to be carried out with the use of catalytic converters. In Australia this was introduced in 1986. Without catalytic converters, vehicles release hydrocarbons, carbon monoxide, and nitrogen oxide. These gases are the largest source of ground level ozone, which causes smog and is harmful to human and plant life. Therefore, with the introduction of catalytic converters to petrol engine vehicles and the introduction of unleaded petrol (Lead is a catalyst poison) for these vehicles, phosphorus levels were needed to be lowered as it is also a catalyst poison. Hence, maximum Phosphorus levels were introduced on some API SH  specification oils.

How much ZINC do you need in engine oils?

There are many and varying opinions on what levels of Zinc are needed to be an effective anti-wearing agent in engine oils. Owners of vehicles that have flat tappet camshafts, veteran & vintage owners and traditionalists may argue that the higher the level the better especially in vehicles that do not have catalysts. This is not always the case.  As we saw above, ZDDP was increased in oils to combat the effects of lead scavengers not actually to increase the anti-wear protection.

In effect, an engine oil that contains about 1000ppm or 0.1% phosphorus (approx.1100-1200 or 0.11-0.12% PPM Zinc) or higher, will easily provide the required anti wear properties for older engines. General Motors experimented in the mid 1950’s with lower phosphorus and zinc levels and found that 800PPM or 0.08% percent phosphorus level (approx. 1000 PPM or 0.1% Zinc) eliminated many wear issues. In fact, they also experimented with oils containing 600PPM or 0.6% phosphorus on mixed fleets in the 1970’s and found no wear problems.

So what is the optimum amount? This will always be a debateable point, depending on the application.

API Specifications

When you add Zinc to an oil, you also add Phosphorus and there have been limits on it since the days of API SH (1994) when a 0.12% (1200ppm) limit was imposed.  Prior to that, in the days of API SG (1989) many manufacturers already had put a 0.10% (1000ppm) limit on Phosphorus.  So, “low” Phosphorus has been with us for quite some time.

The step from API SH to API SL was accomplished by a combination of new additives or adding additional anti wear and anti-oxidant to existing blends.  As an example, the Penrite HPR petrol oils and Pro Workshop upgrades from API SJ to API SL required the addition of these components to pass the relevant engines tests.  These were not Phosphorus based, but used organic molybdenum additives (not molybdenum disulphide) to keep Phosphorus levels at 1000ppm or 0.1%.  Many other companies followed similar routes but there was certainly no loss of protection, even if they started from scratch.

When API SM was introduced - for the first time, the limit on Phosphorus was from 0.06-0.08% (600-800ppm). There were industry concerns about the applicability of these oils in older engines.  However, the limit only applies to 0W-20, 0W-30, 5W-20, 5W-30 and 10W-30 oils (so called “ILSAC” grades).  Any other grades were exempt from this. When HPR 10, 15 and 30 initially went to API SM technology, they maintained their Phosphorus levels of approximately 1000ppm (about 1100ppm zinc).  None of the viscosity grades for these products are bound by the 800ppm upper limit. 

Therefore blanket statements about API SM oils were incorrect and further research will be needed by the end user.  The latest API SP specification has the same limits and ACEA C1 to C6 specifications are also for low Zinc oils.

There is one other factor with non-ILSAC oil grades.  If they also have the European ACEA A2/A3 with B2/B3 or B4 performance levels, Phosphorus levels will also be at 0.10 % to 0.12% as their tests have been more severe than the API for some time.  Hence an oil that is SL (SM)/CF and A3/B3 will also exceed the anti-wear requirements for older engines.

The irony is that API SF and SG oils formulated in recent years usually have Phosphorus contents of around 0.08% (usually 0.1% maximum) anyway due to other advances in technology, unless the blender chooses to add extra additive.

Diesel Engine Oils

Currently, there are no Phosphorus limits outside of grades that are API CK-4/CJ-4 or ACEA E6 (which have limits) – as such many people recommend them for older cars, even though many others say that the detergent levels are too high and the engine will use oil.  Well, you cannot have it both ways.  This one originated from the USA and hence did not take into account European ACEA A/B standard petrol engine oils, which are easy to find in Australia, NZ and Europe, but a lot harder to find in North America.

Yes, the engine may use oil, but only until the cleaning period is complete – unless you are unlucky enough to move a deposit that is stopping oil leaks that is.  However, an engine in good internal condition will run quite happily on diesel oils as long as the SAE viscosity is correct.

Synthetic Engine Oils

This leaves Synthetic oils. Many people say they are too “slippery” for older cars and can cause wear and oil consumption.  Well, wear protection has little to do with the base oil type and everything to do with the additive.  If the wrong anti wear additive is used then it does not matter how good the rest of the oil is, wear will occur.  Hence, the right type of synthetic oil is quite OK in an older car, but unless it is fully reconditioned and then correctly run in, then there is no real benefit to the end user.  It is true that synthetic oils (especially the PAO  type) have lower friction, as their chemical structure allows the molecules to slide over one another more easily than a mineral oil and they also handle heat better for longer than mineral oils, but if the correct additives are used, then this becomes a benefit, not a detriment.

The choice of the correct oil for older cars comes down to various factors such as:

• Original Viscosity Specified
• Condition of engine (leaks, sludge)
• How often the engine is run
• How the vehicle is to be used
• Oil consumption
• Current oil used

Prevent rust and corrosion attack on metal surfaces from acids that can build up in oils, by helping to neutralise their effect.

Rust and corrosion represent the damage done to metal surfaces by the attack of atmosphere oxygen and acidic products. Air is entrained in the oil and fuel, and water and organic acids form during the combustion and decomposition processes. Rust and corrosion inhibitors provide a barrier between the metal surface and these harmful elements. There are 2 types of Inhibitors -

Acid Neutralisers

Basic detergents are excellent rust and corrosion inhibitors, because they provide protection both by neutralizing and by forming physically adsorbed films.

Protective films

The film formers attach themselves strongly to the metal surface and form an impenetrable protective film. The film formation can occur through either physical adsorption or chemical reaction.

Prevent foam from forming, thereby maintaining a lubricating film based on oil not air bubbles, resulting in the ability of the oil to be pumped effectively at the required rate.

Almost every lubricant application involves some kind of agitation, which encourages foam formation through air entrainment.  Excessive foaming will result in -

1. Ineffective lubrication
2. Oxidative degradation of the lubricant

The viscosity of a lubricant and surface tension determine the stability of the foam.

Low viscosity oils produce foams with large bubbles that tend to break quickly.

High viscosity oils generate stable foams that contain fine bubbles and are difficult to break.

The presence of surface‑active materials, such as dispersants and detergents, further increases the foaming tendency of the lubricant.

Foam inhibitors stop foam formation by altering the surface tension of the oil and by facilitating the separation of air bubbles from the oil phase

Additives called Pour‑Point Depressants are used to enable mineral oils to function efficiently at low temperatures.

The “Pour Point” is the lowest temperature at which a fuel or an oil will pour when cooled under defined conditions.

In general, the pour point is indicative of the amount of wax in an oil.  At low temperatures, wax tends to separate as crystals with a lattice‑type structure. These crystals can trap a substantial amount of oil via association, inhibit oil flow, and ultimately hinder proper lubrication of the equipment.

Pour‑point depressants are generally used at treatment levels of 1% or lower. 

VI Improvers change the oils rate of thinning or its Viscosity Index (VI) as the oil heats up. The higher the VI, the lower the rate of thinning of the oil with the increase in temperature. They are polymers that minimize viscosity change with a rise in temperature by expanding as temperature increases – think of them as like a slow uncoiling spring. They also assist in changing monograde oils into multigrade oils.

Oils, are effective lubricants at low temperatures, but become less effective lubricants at high temperatures. At high temperatures, their film‑forming ability diminishes, because their thinning.

Prior to the use of viscosity improvers and the introduction of multigrade oils, this problem was partly overcome through seasonal oil changes.

The principal function of a Viscosity Index Improver is to minimize viscosity variations with temperature changes. They are typically added to a low‑viscosity oil to improve its high‑temperature lubricating characteristics.

There are different types of VI Improvers with better oils using more shear stable types of improvers. Standard "polymer chain" types are more prone to shearing than "starburst" types which results with a drop in high temperature viscosity.

Extreme Pressure Additives act as a barrier between moving surfaces when the lubricant film between the surfaces has decreased to a point where friction can cause wear and damage. This is generally caused by heat generated by the movement and high pressure produced from heaving loading.

There are two main types of EP additives, those that are temperature-dependent, and those that are not. The most common temperature-dependent types include boron, chlorine, phosphorus and sulfur. They are activated by reacting with the metal surface when the temperatures are elevated due to the extreme pressure. The chemical reaction between the additive and metal surface is driven by the heat produced from friction.

Extreme pressure additives are commonly used in Gear Oils, Greases and other lubricants that need to work under extreme load and pressure.

Typical Data is available on Penrite products from the product web pages. Typicals are derived by meauring a typical blend of product during manufacture. The totals may vary slightly between different blends but are characteristec of that particular product. These details are also subject to change without notification if the formulation changes.

Typical Data is the breakdown of components used in the lubricant with key values for areas such as  -

• Colour
• Density
• Viscosity @ 40ºC
• Viscosity @ 100ºC
• Viscosity Index
• TBN
• Zinc levels
• Phosphorus levels
• Sulphated Ash levels
• Calcium levels

Colour is the lubricant colour of the product after blending

Density is a measure of mass. Density = Mass/Volume.

Viscosity @ 40°C is the cST measured at this temperature

Viscosity @ 100°C is the cST measured at this temperature

Viscosity Index (VI) is an arbitrary measure for the change of viscosity with variations in temperature. The lower the VI, the greater the change of viscosity of the oil with temperature and vice versa. It is used to characterize viscosity changes with relation to temperature in lubricating oil.

Total Base Number (TBN) - is a measure of a reserve alkalinity of a lubricant. The test is relevant to internal combustion engines due to the acidic byproducts of combustion generated when gasoline and diesel fuel are burned. TBN levels decrease as the oil remains in service. When the level reaches a point where it can no longer protect against corrosion, the oil must be changed.

Zinc levels are a measure of zinc as a % mass of the oil. Normally shown as "Zinc , Mass %". It can also be related back to "Parts Per Million". A typical example would be a Zinc level of 0.126. This equates back to 1260 Parts Per Million (PPM) Zinc.

Phosphorus levels are a measure of the Phosphorus in the oil. Generally these are very close to the ZInc levels as they are normally put into the oil as an anti-wear package. These are normally shown as Phosphorus , Mass % and can also be expressed as PPM.

Sulphated Ash and Calcium levels are shown same as Phosphorus and Zinc levels.

Cold Cranking Viscosity - The speed-reading is used to determine the viscosity on a calibration curve. The cold cranking simulator (CCS), ASTM D5293, correlates with engine cranking speed at low temperatures. Cold cranking viscosity simulates the viscosity of an oil in crankshaft bearings during cold temperature start up.

Products apart from engine oils may have other Typical Properties such as -Load Tests for Gear Oils and Greases, wet and dry boiling points for brake fluids, Glycol content for coolants plus others. 

A Typical Data page for one of our products will look as follows - It can be accessed by clicking on the Typical Data tab on the product web page.