Aftermarket Crankcase Additives



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Are Aftermarket Additives All They’re Cracked Up to Be? 

I recently got an internet advertisement for an aftermarket oil treatment. The brand is not important, but the concept and presentation speak to many of the conflicting thoughts I have about aftermarket additives, which are often referred to as “snake oil” or “mouse milk.” 

I ’m sure many of you, if not all, have seen advertisements for various additives designed to give engine oils and transmission fluids extra performance features, or at least add to the already strong performance of the oil. I think it is of enough interest that I wanted to share some of my thoughts on the subject. The question is: Do aftermarket oil additives actually add to vehicle performance, or is it just hype?

What do aftermarket additives do? First and foremost, they modify viscosity properties. We all know that viscosity is the fundamental oil property of resistance to flow. Lower viscosity means faster flow, which can be a valuable property. However, for older, high-mileage engines, lower viscosity often translates into more oil consumption, often to the point of an oil slick on the garage floor. It used to be that owners of older vehicles went to higher viscosity engine oils to reduce the losses. I can tell you that modern engines like the 3.5-liter V-6 in my Nissan Quest have solved many consumption questions. Using the recommended SAE 5W-30, it is still not consuming excess engine oil, even after 158,000 miles.

Another important property is wear protection. All modern engine oils have antiwear additives included in the formulation. Some of the older engine designs are based on a so-called flat tappet valve train design. These engines have a larger need for antiwear additives in the oil. That’s usually measured by the zinc content of the oil. While zinc doesn’t actually impact wear protection, the chemical molecule of which it is a part also contains sulfur and phosphorus—the go-to twins for wear protection. They act to form a thin, molecular layer on metal surfaces that wears off without significant damage. Modern engine oils are designed with lower zinc levels in order to improve the emissions performance of the engine per United States emissions requirements.

Oil oxidation resistance is also an important feature for engine oils. When oil oxidizes, it becomes thick and generates byproducts that can be harmful to the engine’s function. The byproducts can really gum up the works, causing piston rings not to function properly and resulting in such things as smoking exhaust. Detergents and dispersants trap the products of oxidation in the oil before it can get to metal surfaces. This prolongs engine life, so the addition of deposit control agents is a big feature.

With all of the interest in fuel economy, friction modifiers are a big part of the story. These materials reduce the friction between metal surfaces. Lower friction means less energy needed to operate the engine, which means less fuel is consumed. The chemistry of friction modifiers is quite variable, including everything from liquids such as fatty acid esters all the way to dispersed solids such as graphite or fluorocarbons. 

When it comes to aftermarket additives, there are a number of major and secondary petroleum additive suppliers that have developed the componentry and data to support marketers’ technical performance claims. But that’s only half of the story, and things get a lot more “creative” in the promotion and sales aspects. Promoting aftermarket additives is one of the biggest parts of the business. Two very common ways to do this are with testimonials from satisfied customers and actual field test programs. 

Testimonials are always a compelling way to tell your story. There is nothing like a satisfied customer to make an aftermarket product stand out. The issue with testimonials is that there is no control or baseline from which to work. In the simplest case, if someone claims fuel economy benefits, there is no way of knowing what the level was before using the additive. 

There’s also the “anticipated results” aspect. When someone uses an additive designed to do something, the expectation of the user is that they will see a benefit. That can lead to unconscious adjustments in behavior, which could influence the outcome. For example, if someone were to add a fuel economy additive, they might not drive quite as fast or accelerate as quickly. The impact could be major.

Field tests are better, provided the test design is carefully thought out. Vehicle choice, driving cycle and other issues have an effect. If they are not controlled as much as possible, the results could be barely more reliable than a testimonial. 

Another way to promote the additives is with some specialized test procedure or apparatus. While these can be very dramatic, they often do not actually relate to the claims made. One of the enduring promotional devices is the “wear/EP” machine. I’ve seen it in many different designs such as lever arms that push a metal piece (often a roller from a bearing) down on a rotating bearing ring. Another version has a device that looks much like a postal scale but does essentially the same thing.

The issue with testimonials is that there is no control or baseline from which to work. In the simplest case, if someone claims fuel economy benefits, there is no way of knowing what the level was before using the additive.

One of my earliest stories about these testers was related to the Kaiser steel mill in Fontana, California. I was working at Richfield Research (later ARCO), and Kaiser was a customer for a grease we supplied. A would-be competitor arrived at the lube engineer’s office with one of the postage scale-like extreme pressure testers. He proudly showed how much load his grease could stand and challenged the lube engineer to see how Richfield’s in-use product could stand. 

When everything was prepared with grease in the lubrication cup, the salesman began loading his weights on the pan. He never could get our grease to fail. He actually took the lube engineer’s paper weight and a piece of steel rod to add to the pan! Even then, the Richfield grease still was chugging right along. Sometimes, the best story can run afoul of a better product.

So, why buy aftermarket additives? For many, there are no specific problems, just the hope that something will be improved. For others, specific issues show up and a quick fix is desired. Here are some of the potential drivers for aftermarket additives:

  • Rust. Rust is one of the leading causes of deterioration in older engines, especially common in small engines such as those found in lawn mowers. It’s also common in seasonal engine applications.
  • Engine cleanliness. Some engine oil additives include detergent components. Engines with sticky parts such as rings or valve train assemblies would be helped by additives that unclog and remove impurities. 
  • Excessive smoke. Stuck rings or excessive wear can result in high oil consumption, which produces smoke. By raising viscosity or including antiwear additives, oil consumption may be reduced. As an extra benefit, it also may reduce engine noise.
  • Oil leakage. Excess oil leakage can be controlled to some degree by seal swell agents. An increase in viscosity has the same effect.
  • Fuel Economy. Reducing internal friction in an engine improves the engine’s efficiency. Friction modifiers help to do just that.

All of that sounds like something that should be available to oil change shops and garages. It could be very valuable in giving your customers the very best protection for their vehicles, but the fact is that every engine oil sold with an API license has additive systems that already do just that. A current performance level (API SP/ILSAC GF-6) engine oil is a complex mix of base stocks and chemical components carefully balanced to provide a level of protection to all passenger cars and light-duty trucks. That’s because API categories are backwards compatible, meaning they’ll protect older engines, including flat tappet engines that call for higher zinc content.

Believe it or not, adding an aftermarket additive to an engine oil may actually make it noncompliant with its API license designation, meaning your GF-6 engine oil could fail to pass necessary test requirements for the category. If a vehicle is under the manufacturer’s warranty, I wouldn’t use any aftermarket additive. If it is out of warranty and appears to need something to help it last longer, consideration can be given to using an aftermarket additive.

All of the owner’s manuals I have seen have specific statements regarding aftermarket additives. There are several versions, but the message is that the automakers frown on their use.

If a vehicle is under the manufacturer’s warranty, I wouldn’t use any aftermarket additive. If it is out of warranty and appears to need something to help it last longer, consideration can be given to using an aftermarket additive.

As I mentioned at the beginning of this column, my Nissan Quest has about 158,000 miles on it and has never seen an aftermarket additive. The engine runs well on an SAE 5W-30, ILSAC GF-4 engine oil, which is my preference.

So the bottom line is this: Follow the owner’s manual requirements while in warranty, and only consider aftermarket products after the warranty has ended. Be sure that the additive you use or recommend actually addresses your customer’s specific problem. I hope your recommendations offer your customers a good ride for a long time.   

Steve Swedberg is an industry consultant with over 40 years experience in lubricants, most notably with Pennzoil and Chevron Oronite. He is a longtime member of the American Chemical Society, ASTM International and SAE International, where he was chairman of Technical Committee 1 on automotive engine oils. He can be reached at