Oil Additives For Diesel Engines - Are They Worth It?

The finished engine oils you buy aren't just petroleum oil pulled out of the ground and slapped into a bottle. They are an engineered combination of refined oil base stocks and an advanced package of different additive components that have been formulated and blended into the oil to make the engine oil function better in important ways.

That’s the biggest difference between the oils of today vs. yesteryear – today's oil has better additive packages that make them more effective and better suited to protecting today’s high-performance diesel engines. You see that reflected in the oil's API Service Category associated with them. The most current service category for diesel oils is CK-4 (which succeeded CJ-4 back in 2017). This kind of designation assures you that your diesel oil meets the most current and necessary specifications to show that it will adequately protect your diesel engine.

Engine Oils Already Come With Additives

The diesel engine oils you buy today will contain important additive components to help with:

Viscosity modifiers

These are added to help the oil maintain its viscosity properties in hot and cold weather. These viscosity modifier additives are what enabled the industry to come up with multiweight oils (think 10W30, for example) that have different viscosity ratings in hot weather and cold weather.

Corrosion and rust inhibitor

These are polar constituents that attract to the metal surfaces in the engine and form a protective film to guard against corrosion.

Detergents

These are essential for keeping metal surfaces free from deposits that form in the engine environment. Typically they will react with any sludge or varnish that has formed and make them soluble so that they can be drawn up into the oil film and away from the metal surface (where they could otherwise cause damage).

Dispersants

Along with detergents, these are essential, too, for keeping those metal surfaces free from the kind of contaminants (like soot) that can damage them. A dispersant will attract contaminant molecules and draw them up (disperse them) into suspension in the oil film.

What about diesel oil additives? What value do they have?

Like fuel additives, there are good ones and bad ones to choose from. But given that diesel engine oils already contain the most important kinds of additives, do you even need an oil additive? Some of them can add significant value.

But it’s important to have a proper perspective on what you think it’s going to do. Since the oil already contains the most essential additive ingredients, the best diesel engine oil additives can provide value by supplementing what’s already in there. There’s value in this because these additives get used up over time. The dispersants, acid neutralizers, and detergents get used up as they perform their essential functions. So adding a diesel engine oil additive can provide value by extending the period through which these essential additives last.

A good oil additive can also enhance the oil’s extreme pressure characteristics (its EP properties) by adding some kind of constituent that improves the oil’s ability to provide and maintain lubrication under extreme pressure. However, don’t buy into the idea that oil is completely lacking in this regard. All oils have some level of EP additive already in them. ZDPP was the market choice for a long time but today's diesel emissions control system can be damaged by the ash that ZDPP made. The market developed alternatives (like ionic liquids) to try and replace ZDPP's benefits. They may not work quite as well but they're better than nothing. And so, in this respect, an oil additive can provide an extra benefit by supplementing this EP protection (depending on what it is, of course).

So what you don’t need is an oil additive that makes claims that engine oil just doesn’t contain a specific kind of essential component that, through its absence, is going to destroy your engine (unless you buy their additive, of course). That’s severe overmarketing. Reputable oil additives of high quality that do what they claim will not need to oversell themselves.

You may be interested in these related posts:

• Are diesel fuel additives worth it?
• Diesel Oil Additives: Any Difference?
• Carbon buildup in diesel engines