How does the grade, cetane number, and fuel additives affect your diesel vehicle’s performance?

Most diesel owners roll into a fueling station, giving little thought as to the quality of the diesel flowing into the tank, or how it affects the power and fuel economy of the diesel engine under the hood. Diesel owners just pop open the filler door, insert the filler nozzle, push the diesel button on the island, and go about filling the tank.

All for good reason: while gasoline typically is offered in three or four grades based on octane level, most diesel pumps found at gas stations offer just one – #2 Diesel – the quality of which is unknown to the person filling their diesel’s fuel tank.

“The quality of diesel fuel varies from state to state; in fact, it can vary from station to station which makes understanding exactly what type of fuel is running through your motor kind of difficult,” says Josh Steinmetz, the brand manager for Lubrication Specialties, Inc, the maker of Hot Shots Secret. “The cetane and lubricity levels can vary even in the same fueling station chain depending on the base fuel brought in.”

Why are cetane levels and lubricity important? Because those two items have a direct relationship to a diesel vehicle’s overall performance, fuel economy, and durability.

Paying close attention to the quality and treatment of the fuel that powers hardworking diesel pickups is a good way to maximize engine life and performance.

The Difference Between #1 & #2 Diesel

When it comes to vehicles driven on the highway, #2 diesel is what is considered the standard, commercial grade diesel fuel. It contains paraffin, so it burns about 10-percent hotter and makes more power-per-gallon than #1 diesel fuel. Another difference is #1 diesel has a higher cetane rating than #2. A higher cetane number is helpful during the winter months. “A diesel fuel’s cetane rating tells you the ignition quality of the solution — the higher the cetane rating, the easier it is for diesel-powered trucks to perform a cold start,” says SC Fuels, one of the oldest and largest, family-owned petroleum distributors in the United States.

“Choosing 1-D [#1 diesel] fuel gives you more cetane within the mixture, which reduces the stress placed on the cranking batteries,” adds California-based SC Fuels. “And, unlike 2-D [#2 diesel], it also contains additives such as lubricants that reduce the amount of friction on internal fuel system components, which helps increase vehicle life expectancy. Also, #1 diesel contains detergents that prevent the buildup of sediment from interfering with performance.”

While drivers of gas-powered vehicles have multiple octane choices when filling the fuel tank, diesel owners
get just one, and that’s usually #2 diesel with an unknown cetane value.

Diesel BTU Dictates Power

In a nutshell, #1 diesel fuel, which has no paraffin, delivers about 125,000 BTU of energy per gallon while #2 diesel has a heat value around 139,500 BTU. For diesels driven in high-temperature environments, #2 is best because of its consistency and better fuel efficiency than its counterpart. At the same time, it’s prone to gelling when outside temps drop below freezing.

“Paraffin wax (naturally found in Diesel #2) will always crystalize when the temperature gets down to 14 degrees Fahrenheit,” explains Jenny Oujiri, a senior marketing specialist with Cenex. “There’s a special fuel additive called a cold flow improver (CFI) that dissolves the bonds in paraffin wax. By breaking up larger crystals into many smaller parts, a CFI enables paraffin wax to pass smoothly through the filter. Typically, a CFI is effective down to about zero degrees Fahrenheit.”

Adding a diesel fuel supplement designed to reduce the ill-effects of gelling when outside temperatures stay
below freezing is a good practice. So is using diesel fuel that’s a blend of #1 and #2 diesel.

The Difference Between Summer & Winter Blends

The diesel fuel gelling issues with #2 diesel is why regional wholesale fuel suppliers offer a winterized fuel “blend” during winter months. When the outside temperatures stay below freezing, Qujiri recommends fuel suppliers use a blend that’s 30 percent # 2 and 70 percent # 1, while continuing to mix in a CFI.

Blends of this nature retain the higher BTU characteristics of #2 with the freer-flowing, lower viscosity and the higher resistance to gelling of #1 diesel fuel. If you’re not sure if your local refueling station is selling the winter-blend diesel, or you are heading to an area where daytime temps never get above freezing, run #2 and treat with a fuel additive such as Hot Shot’s Secret EDT + Winter Defense fuel booster.

Running diesel fuel that has a high cetane number helps improve cold weather starts. Winter-blend diesel
fuel reduces the chances of it gelling when outside temperatures stay well below freezing.

What Are Cetane Numbers

It’s crucial to understand the difference between “cetane” and “cetane number”(CN). Cetane is a set of natural occurring chemical compounds found in diesel. A cetane number is a number derived from testing a sample of the diesel fuel to determine how quickly it ignites inside the engine; the higher the CN, the more easily the diesel engine starts. CN has nothing to do with horsepower or torque output of a diesel engine.

“The cetane number is only a measure of ignition quality of diesel,” according to Pam Rosen, a general manager for Shell’s Fuels, Lubricants and Motorsports division. “The cetane number of a given diesel fuel is obtained by matching its ignition quality to a reference blend of cetane (set at 100) and iso-cetane (set at 15) and hence the name ‘cetane number,’ or CN. Diesel fuels with a higher CN ignites faster, producing a longer, cleaner fuel burn than diesel with a lower CN. (#1 diesel fuel typically has a “cetane” rating somewhere between 51-53, while #2 diesel cetane numbers range from 40-48.)

A cleaner fuel burn means less emissions. That’s why the EPA set a minimum CN of 40 across the country, with the final CN left up to individual states’ emissions regulations. For example, the California Air Resources Board (CARB) currently mandates a minimum 53 CN, Texas sets its highway diesel CN minimum at 48, while Oregon’s minimum is 47. The rest of the country’s non-bio diesel can vary in CN from 40 to 60, depending on a lot of variables from the initial refining process to the time it flows out the end of the nozzle and into our truck’s tank.

One popular choice among diesel fuel additives is Hot Shot’s Diesel Xtreme, which is very concentrated,
multi-purpose treatment that improves cetane number, adds lubricity, cleans injectors, and acts as a fuel
stabilizer.

Diesel Is Diesel

There’s the catch: there’s no way to know what mixture of diesel coming out of the filler nozzle at the local gas station. It could be straight #2 diesel. It could be a blend of #1 and #2. The CN could be 40, or it could be 50. The commingling of highway diesel fuels makes the determination of what is actually going into your diesel engine is nearly impossible to know because it could have been mixed with diesel of a higher/lower CN in holding tanks where it was stored. The fuel wholesaler could have mixed in their own additive package with a cetane booster, or the diesel in the filling station’s underground tanks that it mixed with before reaching your truck’s fuel tank may have had different cetane numbers. Or, the amount of fuel left in your truck’s tank before adding the new diesel could be different in both CN and additives. Hence, the adage that “diesel is diesel” carries a lot of truth.

The literal heart of any diesel engine is the fuel-injection pump. It requires a certain amount of lubricity in the
diesel fuel to maximize its service life. Today’s Ultra-Low Sulfur Diesel (ULSD) does not contain such lubricity
without the aid of a diesel fuel additive.

Commercial Grade Diesel Quality

The bad part about such cross-mixing of diesel between the refinery and the diesel pump at your refueling stop is there’s no regulation that requires the actual CN of the diesel (or the blend during winter) coming out of the nozzle to be posted, as is done with gasoline. All you know for sure is it’s at least the “minimum” as required by the fuel authority for your area.

“As a [diesel fuel] retailer, the goal is to buy the lowest-cost fuel that meets the minimum requirements for the area,” says Josh Steinmetz, Brand Manager at Hot Shot’s Secret, the fastest-growing diesel additive brand. “It’s all about saving a penny or two per gallon—multiplied by hundreds of millions. But that leaves everyday diesel owners with fuel that lacks the necessary protection and performance enhancers.” That’s why diesel owners should consider regular use of a premium diesel additive that boosts both the Cetane number as well as adds lubricity to the fuel. This would help maximize the fuel-injection system’s longevity and optimum performance.

The shelves at stores that sell automotive lubricants and fuel additives are loaded with products for diesel applications. Think of a multipurpose diesel fuel additive, such as Diesel Extreme, as a multi-vitamin for diesel fuel.

Best Diesel Fuel Additives

Diesel-fuel additives are a lot like medicine: use them to remedy an ailment, or ailments, afflicting your pickup’s engine as prescribed by an expert who diagnosed those problem(s). “This goes back to using a multifunctional additive that boosts [CN], cleans injectors and provides the necessary lubricity to protect fuel pumps and injectors instead of only chasing a higher cetane number,” Steinmetz told us. “We recommend our Everyday Diesel Treatment (EDT) at each fill-up to make even the worst pump fuel into a premium diesel with its 6-in-1 formula that boost cetane and lubricity while protecting against water and other common issues with diesel.”

Making such a treatment part of the regular fueling cycle is a way to be confident the diesel fuel pouring into the fuel tank has the needed amount of detergent, cetane and lubricity to keep your diesel rig’s engine and fuel system healthy.

The plunger and roller inside a Bosch CP3 diesel fuel injection pump rely on lubricity in the fuel to function
properly. Lack of proper lubricity results in catastrophic failure.

Be Careful When Using Fuel Additives

Diesel additives vary greatly in how they are made. Increasing the recommended dose of some diesel additives can lead to changing fuel density and reducing overall engine performance, according to some diesel experts we spoke with. It’s best to “use as directed.”

“We have tested with 10 times the recommended dosage of Diesel Extreme with no issues,” states one of the technicians at Lubrication Specialties Inc. “Over usage is just wasteful, as the strong formulation in our additive already pushes the boundaries of diminishing returns.”

The short take of all this is the fuel going into our diesel vehicle’s is of an unknown quality, and to maximize any diesel vehicle’s engine’s longevity and overall performance is to use an additive. Adding a cetane-improver, by itself, will not magically improve your diesel’s quarter-mile times and trailer-pulling abilities.

What regular dosing the fuel tank with additives that include CN boosters, injector cleaners, and lubricity improvers will do is ensure the diesel engine in your vehicle starts easily when cold—and the fuel system, from the injection pump to the injectors, runs cleaner, smoother, and has a longer service life than it would without such a fuel treatment.

Some diesel supplements are designed for winter use to prevent #2 diesel from gelling when the outside temperatures the vehicle is used in stays below freezing.