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Oil Additives explained

What are the typical additives in my engine oil?

Additives are usually chemicals dissolved within the oil and act on the contaminants and components rather than on the oil itself.  They either coat the surfaces of the components or surround the particles or droplets of acids or moisture.

These additives are typically:

How does a Friction Modifier work? 

Figure 3 - Load, Friction Control and Friction Modifiers preventing Seizure

Two similar dry surfaces in contact will experience friction and with increased loading, seizure will result.  Wetting the surfaces with oil will reduce the friction but ultimately seizure will still occur.

Adding Fatty Acids or oiliness agents will help, but beyond that, AW (Anti-Wear) additives are needed, and then EP is required. 

The Friction Modifiers work by modifying the component surface making it more ductile and reducing the friction coefficient.  Think of two bars of dry soap, and then how slippery they become when wet.  AW is less aggressive in this way than EP, only modifying the surface to a depth of less than 0.1µm as compared to EP which works to a depth typically of 0.5µm.  Under load, and thus increased temperature, the friction modifiers react with the surface to make it more ductile and reduce the friction accordingly.  The layer remains in effect but may under some conditions be lost through excessive boundary contact.

AW is usually ZDDP or to give it its full name, Zinc DialkylDithioPhosphate.  Owing to the use of exhaust catalytic converters (exhaust gas aftertreatment) and the environmental push to limit Zinc and Sulphur, newer oil formulations have reduced levels of Zinc.  Consequently there has been some discussion to suggest that this may affect the wear rate of the flat topped cam followers used in older engine designs.  

The fact is that the levels of ZDDP in modern oils are still sufficiently high enough to protect most classic engines, and today’s oils still have as much as 4 times the amount of ZDDP by comparison to oils formulated in the early 1960s when the A and B Series were first used in production cars.  Whilst newer engine designs differ from older designs, the newer oil formulations more than compensate for wear protection by having differing formulations for AW protection.  

All parts of the modern engine still need some AW and mild EP protection during start-up when the engine surfaces are ‘dry’ and speed is insufficient to achieve thick film lubrication and the crucial separation of the components. A point to note is that some of this protection layer is lost during a cold start and also that AW and mild EP require heat to activate.  Therefore a cold engine is susceptible to greater wear during the warming up period, in my opinion.

For many applications Fatty Acids or Oiliness Agents and AW are sufficient.   For extreme loading such as experienced in an axle differential, EP (Extreme Pressure) additive is used. EP is like an AW additive, except that it is formulated for extreme loading, and acts more aggressively on the metal surfaces.  It is often a sulphur phosphorous base, hence the distinctive smell, and the active Sulphur may attack yellow metals such as copper or bronze in high temperature environments.  Therefore, it is necessary to restrict its use to the differential only, and avoid use in a gearbox with Copper based synchro-mesh rings unless otherwise stated as ok for use by the transmission manufacturer.  Its use should also be avoided in gearboxes that use a cone/friction clutch (Overdrive) as slippage and increased wear will result.  

What about these aftermarket additives?

Ask any supplier of aftermarket additives these few questions:

Then ask yourself why:

The oil's original additive formulation is in fact a compromise of all the needs of the oil and the machine for which it is blended.  The adpac formulation must take into consideration all the additives that act on the surfaces and ensure these are given due consideration for space.  By altering that balance, some of the original adpac will be excluded from the component surface, resulting in issues like longer term corrosion and rust, as well as potential problems with the oil such as foaming etc.

Some aftermarket additives are an additional form of anti-wear relying on Chlorine.  These may look impressive in the simple demonstrations given at trade shows but like a magician, this simple test won’t let you see all that you should be seeing.  The Chlorine can be corrosive and a potential health hazard.  The simple test rig may show evidence of removing the scars, therefore by implication, excellent wear control and even repair of existing damage, but what has happened to the surface profile as a result of that polishing action?  Another element of these simple demonstrations is the ability to continue operating under increased loads – but if these high loads were to be encountered in an engine, then the oils would have been formulated accordingly.  When one considers what a drum of this additive costs – very little – and what they sell this additive for in little 100mL bottles – a lot - then do the mathematics and figure out how much money is being made here, often from a domestic garage on a typical housing estate.

Other forms of aftermarket additive formulation include solid lubrication such as Molybdenum Disulphide, graphite and PTFE (or Teflon – a trademark of DuPont and licensed for use by Interflon). In all these cases, it is a solid suspension additive in the oil. The filters will either remove much of these solid suspensions or the suspension will settle to the bottom of your sump.  These oil additives are possibly better suited to use in something like a gearbox or differential.  But again, care should be taken.  Friction is not always your enemy.  Rolling element bearings and synchromesh rings require some friction to ensure their successful operation. Too little friction and the rolling elements will then slide instead of rolling, resulting in flat spots and possible collapse of the bearing.

Worse yet…

NASA Lewis Research Center:

"In the types of bearing surface contact we have looked at, we have seen no benefit. In some cases we have seen detrimental effect. The solids in the oil tend to accumulate at inlets and act as a dam, which simply blocks the oil from entering. Instead of helping, it is actually depriving parts of lubricant"

In a University of Utah study:

"There was a pressure drop across the oil filter resulting from possible clogging of small passageways. Oil analysis showed that iron contamination doubled after the treatment, indicating that engine wear increased”

In theory, these solids look attractive and can repair pitted surfaces on gear teeth, but in practice they have been known to clog oil ways and filters.

Some of the claims look attractive, but I often see no supporting evidence save for the anecdotal evidence given by “satisfied customers” and dubious science lessons from fading celebrities. In fact several years ago the FCC in the US fined one additive purveyor US$10million for false advertising. They were unable to prove their performance claims of less wear and more reliable engine performance compared to normal motor oil alone.

There have been many independent studies on Slick 50, the most noteworthy include the National Research Council in Canada and South – Western Research Institute under the sponsorship of GM. None of these studies have found benefits and many have found drawbacks. Typical drawbacks reported in the literature and users include:

As with all aftermarket additives there are the usual problems such as:

Aftermarket additives can, and do, have their place where used with caution for such operations as flushing, seal enhancing on a leaking unit and perhaps improving EP performance in a gearbox, but in the main my strategy is to buy the best oil, fluids and fuels I can justify.

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