All about oil

Aftermarket oil additives

The vision of ever-lasting oil coupled with misconceptions in the minds of the buying public have created a wide-open field for aftermarket oil boosters. We often hear the claim that oil does not wear out, but it does get contaminated and that the additive package becomes depleted. For the most part this is true. However, oil also can be cooked to death, at which point the additive package does not make a bit of difference.

Aftermarket additives can be divided into three main categories: Friction modifiers, oil rejuvenators, and oil consumption reducers. Each is different, although you should think twice before using any of them.

Friction Modifiers

Friction modifiers promise less wear during starting, improved mileage, smoother engine operation, and cooler running. To some extent, a few of them can deliver what they promise. For that matter, there are some commercially available oils with exotic friction modifiers already built in. These would include compounds such as graphite, molybdenum disulphide, and the more expensive molybdenum dithiophosphate. These are all laminar in composition, and act like a stack of playing cards under stress. That is, you can press downward on the top of the deck without compressing it much, yet the cards will slide relative to each other. If you put that same type of sliding action between the moving parts of your engine, you go a long way towards eliminating boundary lubrication.

One of the claims you will hear about friction modifiers is that they go to hot spots in the engine (where lack of lubrication has allowed friction which in turn creates heat). It sounds like magic, but it is really just plain old chemistry. Taking molybdenum disulphide as an example, the sulphide portion of the molecule has a high affinity for hot metal. When it attaches itself to the localized hot spot it drags the moly along with it. The moly eventually will plate out on the metal and provide lasting protection. Moly dithiophosphate does the same thing only with phosphorus instead of sulphur.

Friction modifiers of all descriptions are readily available for supercharging your oil, but some notes of caution are in order. Many oils are painstakingly compounded. Some will accept aftermarket additives, some will not. When they won't, the difference often is not pronounced, you just do not get your money's worth — either of the oil or the additive.

For example, the detergent package in the oil may view the aftermarket friction modifier as some form of contamination. By attacking the friction modifier, the detergent package becomes depleted and the friction modifier is at least partially neutralized. To look at another case, any oil booster that promises to plate out in the motor may also shield the metal from the beneficial effects of the other components in the oil package.

In other words, most of the name brand oils have been blended to provide all-around performance. So while it may be possible to improve the performance in one area by using an aftermarket oil booster, it is also possible that you will be losing the balance provided by ensuring your motor has a clean supply of premium quality oil.

Another thing to consider is that some friction modifiers burn less cleanly than straight motor oil. This can mean anything from premature spark plugs fouling to gritty contaminants that grind away at the very surfaces they were added to protect.

If you do find one that works, however, remember not to use it in a freshly built (or rebuilt) engine. Allow the motor to accumulate 3,000 to 5,000 miles of break-in time before pouring in your super additive.

Oil Rejuvenators

The second category, oil rejuvenators, promises extended life from old oil, and new life for tired engines. These products are based on the premise that the base stock has not worn out but that the additive package has been used up. It is also assumed that the proper proportions of the oil rejuvenator can be calculated by the average customer. On the main, oil rejuvenators would be of benefit more to motorists with high-performance filtration systems. For the rest, temporary (and partial) benefits are possible, but in the long run these products promise more than they can deliver.

Consumption Reducers

The final category, oil consumption reducers, promises just that: Reduced oil consumption, usually in older cars. It would appear that the only way to do this is to thicken the oil. It is significant that consumption reducers rarely claim increased fuel economy.


This is by no means an exhaustive treatment of all the oil additives on the market. However, a test conducted by the U.S. Army Mobility Equipment Research and Development Command on the characteristics and effectiveness of 18 different additives concluded that many of the aftermarket additives did little to aid the detergency or dispersant qualities of the engine oil, while some actually created potential problems in the areas of foaming and thickening of the oil.

So if you are trying to stretch the service life of a tired old motor, experimenting with oil additives might be a lot of fun. For a sound motor with the potential for many miles of good use ahead of it, you cannot go far wrong with regular oil changes, sans aftermarket oil boosters.