Maintenance Q&A
Additives and the debates that wage on

By Paul Abelson, senior technical editor

Q. I bought a 2009 Freightliner Cascadia with a 500 horsepower Detroit Diesel DD15. It has only 375,000 miles and a year’s worth of warranty left on it. It’s the first truck I ever owned, so I have no experience to go by. Since the day I got it, I’ve been bombarded with truck stop wisdom from other drivers, especially those who do their own maintenance. Specifically, I want your opinion on oil and fuel additives. I’ve been told to use them and not to use them. Those who tell me to use them all have different brands they recommend. What is your advice?

A. I have been following fuel and oil additives for many years. Before I share my personal conclusions, I should present both major brand oil refiners’ positions and additive makers’ counter arguments.

The refiners who manufacture and package engine oil say that additives are not needed with good quality oils. They start with base stocks, either refined petroleum or synthetic bases. They then blend in their formula of additives that provide specific properties to help the finished product do its assigned functions. Some of the additives are created in-house, while most are purchased from specialty manufacturers.

Oil is more than just a slippery film that keeps moving parts meshing or sliding freely. According to the American Petroleum Institute, here’s what engine oil does: It provides a tough film that seals combustion gases in the cylinder and prevents them from being blown into the crankcase. It cools the engine by absorbing heat, then releasing the heat through a heat exchanger. Oil protects parts exposed to air and corrosive gases from rust, corrosion and oxidation.

Those tasks are accomplished by the base oil.

But other tasks require the blender to use additives. There are detergents that loosen soot from engine parts, as well as suspension agents that hold soot and fine metal shavings in the oil so they can flow to filters. These also provide the alkalinity that neutralizes acids formed in combustion. Viscosity improvers help oil stay thick when it’s hot but allow it to flow when cold. Friction modifiers lower internal drag. Foam suppressants prevent churned oil from entraining air so only liquid is pumped through the engine.

These chemicals make up 25 to 35 percent of oil’s volume. They are in delicate balance so they do not negatively affect performance. Oil refiners test their oils not only for performance, but for compatibility in combination with oils from major suppliers. That allows us to safely top off with other brands. Additives, the refiners claim, can affect the balance and degrade their oil’s performance and service life.

Additive makers counter by claiming that their formulations augment the best properties of commercially available oils and extend oil life. Their claims are based on properties of the chemicals they add. Increasing detergents extends life. Increasing friction modifiers improves fuel economy, and so on through the additives. The largest blenders also test their products with the most popular oils, alone and in combination. They stand behind their products. That’s why I would be confident using, for example, Lucas Oil products while avoiding “Bubba’s Bodacious Engine Oil Elixir.”

Engine makers, including Detroit, recommend using only oils that meet current American Petroleum Institute (API) Service Classifications. For your engine, that would be CI-14 plus or CJ-4. If you have a warranty issue with your engine lubrication and you use an additive, their first reaction may be to disallow warranty. This is where a major oil additive supplier will go to bat for you, and it’s why the strong survive.

Fuel additives are a different story. I believe they are necessary to improve diesel performance and to keep your engine operating as it was designed to do.

Unlike gasoline which may have specific chemical additives blended into it at the refiners’ terminals, most diesel is bulk pipeline fuel. Its additives protect the pipeline, not your truck. It must meet minimum standards that define diesel fuel and no more.

As soon as diesel fuel is refined, it starts to degrade. Oxygen, moisture and organisms from the air attack the fuel. Poor housekeeping practices at truck stops can affect fuel in the tanks. That’s where additives help.

Many drivers treat fuel only in winter to prevent gelling and icing up. It is important to lower the fuel’s pour point and control water. But other problems occur year round.

Additives can form a barrier between fuel and water condensed in tanks, inhibiting organic slime growth. Detergents keep injectors lubricated and nozzles clean so spray patterns do not deteriorate. Additives increase lubricity lost when refining ultra-low-sulfur diesel (ULSD), keeping the fuel system adequately lubricated. Finally, cetane improvers make starting easier for cold engines.

As with oil additives, fuel additives come from many sources. At one time, more than 500 local and regional brands were available, but only a few achieved national recognition. I would stay with one of the major suppliers.

One word of caution: Follow label directions precisely. This is not a case where, if one is good, two are better. Some of the chemicals can aggressively deteriorate hoses, seals and even metal parts when used in too high a concentration. LL