Improving diesel engine performance and component life

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Improving diesel engine performance and component life

Diesel engines are the proven sweethearts of the transportation industry. I’m sure you’re seeing more and more in your shop, given their increasing popularity among light- and mid-duty pickup truck owners. They’re basically for anyone who needs to carry and/or tow heavy loads. While a diesel engine tends to create its peak horsepower and torque at lower rpm ranges than a gasoline engine, diesels are commonly known for their ability to offer greater torque. If maintained properly, a diesel engine will typically offer a vastly superior lifespan as compared to a gas engine. And in the “old days,” diesel fuel cost less than gasoline. So when you add it all up, it’s no mystery why those who towed loved their diesels.

However, thanks to tightening emissions mandates, changes have been made to today’s diesel fuel, which offers less lubricating benefits for the fuel system and exhaust valves, and it carries a heftier price tag at the pumps due to the increased refining cost required to meet Environmental Protection Agency (EPA) rules.

Today, your customers who run light-duty diesel engines need to pay more attention to both the fuel and the oil that they use and to be aware of the need for specific additives/treatments in order to boost their vehicles’ performance, avoid drivability issues, increase their mileage and prevent premature injector wear.


Diesel fuel’s cetane rating is similar to the octane rating of gasoline. The cetane rating (CN) is a measurement of the combustion characteristics of diesel fuel. Since a diesel engine ignites its fuel through the use of compression (while a gas engine uses a spark to ignite the fuel), the cetane rating must be high enough to allow the fuel to ignite as the cylinders build compression.

The “knock” that is heard when a diesel fires is the result of the initial fuel igniting after an initial delay. Once the engine fires, the resulting fuel flow ignites more smoothly. A higher cetane rating shortens this initial ignition delay (because higher cetane rated fuel ignites more easily). Typical cetane ratings in diesel fuel sold in the U.S. carries a cetane rating in the 40 to 55 range.


Relatively speaking, higher cetane fuel offers more efficient combustion, superior cold-starting, reduced chance of misfires, reduced engine knocking and reduced white smoke during warm-ups. Just as higher octane gasoline improves engine performance on higher compression engines, higher cetane levels provide better diesel engine operation. Cetane (also known as isocetane), ignites easily. In the proper levels when formulated with diesel fuel, the fuel is easier to ignite under lower levels of heat. The shorter ignition delay improves cold startup and benefits engine power output. Cetane ratings have nothing to do with fuel quality, rather, cetane is a combustion enhancer. Naturally, just as with gas engines where there’s no benefit to running a higher octane rated fuel than is specified by the automaker, there’s no benefit to running a higher cetane rating in a diesel engine than is specified by the vehicle maker.

Aside from cold starts and overall performance issues when running diesel fuel with too-low a cetane rating, this can also increase, or accelerate, the buildup of oil sludge in light-duty diesel engines.

If cetane is too low for the application:

•  there’s an increase in oil sludge,

•  reduced engine power,

•  increased engine noise,

•  increased white smoke on starts,

•  increased exhaust emissions,

•  increased engine wear,

•  decreased fuel economy, and

•  engine startup difficulty in cold weather.

If the cetane rating is too high for the application, this can cause problems as well, such as an ignition delay that is too short, the timing of the pressure peak changes, resulting in many of the same problems associated with running too-low a cetane rating. If cetane is too low, many of the problems may tend to diminish as the engine warms up to full operating temperature, while too-high a cetane may cause persistent issues even after the engine warms up.

“Performance” diesel engines tend to operate better with a cetane value of 50 or higher. Considering today’s ultra-low sulfur diesel fuels available at the pumps, using a cetane boost additive can bump values up by as much as seven points (depending on the specific additive).

With all of that said, while cetane level is important, adding cetane boosters to the fuel system is only critical for high-horsepower diesel applications and isn’t as great a concern on daily driver applications.


Oil additives

Tell your customers that all diesel applications can benefit from a dedicated diesel oil additive that increases lubricity for the injector system and turbochargers. However, the really critical need for such additives involves any diesel engine that features an external high pressure oil pump that runs the injectors (such as with the Ford Powerstroke 7.3L Navistar). Other designs utilize a high pressure fuel pump that provides pressure pulses based on engine speed.

A current technology common-rail fuel system features a fuel pump that pressurizes the fuel system, fed through a common fuel rail that feeds the bank of injectors. The injectors fire according to signals from a control module. In the designs that use a high pressure oil pump to energize the injectors, this oil pump provides hydraulic pressure of around 4,500 to 4,700 psi for injector operation, which essentially cooks the engine oil as it circulates through the entire engine. Additives such as zinc, Teflon, etc., are used by some additive makers, while non-solids potassium boride (as used by Rev-X, for example) is also a lubricity enhancer that blends with the oil and won’t separate over time. Personal preferences aside in terms of additives, any Ford Powerstroke that features a high pressure oil pump needs an additive that will enhance lubrication and reduce operating heat.

Extending the oil’s ability to reduce friction results in several benefits, including helping the turbo to spool quicker and to reduce or eliminate cold-start issues.

Ultra-low sulfur diesel fuel

Here’s where we get into the category of “must use” additives. ULSD (ultra-low sulfur diesel) is a “cleaner” version of diesel fuel mandated by the EPA that contains 15 parts per million or less of sulfur content (replacing low-sulfur diesel fuel which was rated at 500 ppm), which began phasing into the U.S. starting around 2006.

As of December 2010, all highway (on-road) diesel fuel sold in the U.S. had to be ULSD. The reduction of sulfur content is aimed at reducing NOx emissions and soot particulates.

That’s good news for the environment, but potentially bad news for diesel fuel systems.

The reduction in sulfur also reduces the fuel’s ability to lubricate diesel fuel injectors and related fuel system components. (By the way, “sulfur” is the U.S. spelling, while “sulphur” is the British spelling).

The challenges brought about with the use of ULSD includes accelerated wear of fuel injectors and pumps. ULSD also features poor cold weather operation, requiring additives to prevent gelling and to increase cetane level.

Sulfur helps to create an extreme-pressure lubricant (sulfur is routinely added to grease and oils to increase lubricity). The sulfur content in diesel fuel helps to lubricate diesel engine fuel pumps, fuel injectors and fuel control valves. In reality, by cutting sulfur content down to 15 ppm, sulfur has essentially been removed from today’s diesel fuel. Since ULSD is also less viscous (thinner) than previous grades, this can cause problems in older diesel engines that were designed to use higher sulfur content fuel. The thinner fuel has a better chance of leaking (at connections, etc., where a more viscous fuel would not be able to pass through). The thinner viscosity also provides less of a “cushion” for moving parts (such as valve, seats, etc., in fuel injectors). We’re assuming this is an area of concern for diesel engines made prior to, say, 2010.


Whether the engine features a high pressure oil pump to run the injectors or a common-rail system that relies on the fuel pump pushing fuel through a common rail to all injectors, keeping the injectors clean and lubed is absolutely critical. Because of the reduced sulfur content of today’s fuels, we need to supply additional lubrication in order to prevent injectors from sticking. Considering that replacement injectors (depending on the application) can run your customers anywhere from $300 to $800 each, it’s easy to understand how important it is to minimize sludge buildup and wear.

Diesel fuel additives applicable to today’s ultra-low sulfur fuel, depending on the specific products, are capable of providing any or all of the following:

•  several point cetane boost,

•  improved cold starts,

•  Increase lubricity

•  enhanced cleaning of the fuel system   (re: detergents),

•  reduced system wear,

•  reduced exhaust gas temperature,

•  reduced emissions,

•  increased engine performance,

•  extended fuel storage life, and

•  potentially improved mpg.

In short, while the automotive industry has been flooded with additives of all sorts for decades (some worthwhile, some nothing more than snake oil), assure your customers that the need for oil and fuel additives for diesel engines is not a myth. The need is absolute and cannot be disputed. For extended system life, drivability and performance, all of your diesel customers need to take a hard look at selecting and using the diesel oil and fuel additive packages that are available today.

Biodiesel fuels

As noted by Power Service (additives manufacturer), as pressure increases to lessen America’s dependence on fossil fuels, biodiesel is more widely used as a blended component of diesel fuel. Some states have mandated that all diesel fuels contain varying percentages of biodiesel, and the U.S. government has authorized a B20 fuel (20% biodiesel and 80% diesel fuel) for use in all “non strategic” applications. Poor cold weather performance, high water content and microbial infestation require biodiesel fuels to be treated for reliable performance.

In other words, the quality of today’s at-the-pump diesel fuel ranges all over the board, from lousy to good. To play it safe, diesel owners need to take a serious look at adding treatments that will protect their investments. If you consider only the replacement cost of eight fuel injectors, which can easily be in the $2,400 to $6,400 range, it doesn’t take a rocket scientist to realize the importance of keeping the fuel clean, water-free and lubed. The days of simply topping off the tank and hitting the road are gone. Diesel owners will either spend a little now or spend a horrific amount later.

Additives of critical importance

In order to gain further insight into the subject, we enlisted the expertise of one of the industry’s experts. The following are comments provided by Penray Companies Inc. Chief Chemist Steve Muth.

Your customers with diesel-powered vehicles might not be aware of the changes that have taken place in fuel chemistry over the last decade or so. Long-time owners and operators know of the dramatic reductions in sulfur content, down to the current 15 parts per million maximum limit, and some of the problems that have been attributed to the dramatic drop from the old 500 ppm limit.

The change has been necessary to reduce the environmental impact of using diesel fuel by allowing the use of exhaust after-treatment systems. Unfortunately, users have observed drawbacks in terms of drivability, performance and fuel economy.

There are a number of areas of concern using these new-generation fuels. Reduced sulfur content, or rather the process of removing the sulfur, contributes to reduced lubricity, lower energy content and poor ignition properties. All diesel additives on the market today are required to be “ULSD-compatible,” but that doesn’t mean they address any or all of the problems associated with ULSD.

Properly formulated additives can correct problems by increasing cetane, enhancing lubricity, and keeping the entire fuel system clean to maintain peak performance and efficiency of the engine. Increased levels of asphaltenes in diesel fuel have been attributed to the process used to reduce the sulfur content. The chemistry just doesn’t make sense; ULSD should have less asphaltene than ever before.

The fact remains that you are seeing “black fuel” showing up in vehicles and plugging up fuel filters. This black contaminant responds to chemical treatments the same as asphaltene, so a good anti-asphaltene fuel system cleaner takes care of the problem. In addition, sludge and bacterial growth can build up in the fuel system, especially in the warmer, wetter months. This can be especially prevalent with the increased use of bio-fuels in warmer weather. Tell your customers that regular use of a year-round diesel fuel conditioner can minimize such problems.

As you know, cold weather is problematic to diesel engines, causing gelled fuel and ice formation that plugs lines and filters. This issue continues with the new-generation ULSD fuels and is worse with bio-fuel blends.


However, this problem can be addressed through the use of an appropriate cold weather specific additive. (Editor’s note: One example is Penray’s Winter Pow-R Plus diesel fuel treatment), which tests have shown significantly reduce your fuel’s cold filter plug point down to -30º F. The company’s Hybrid Antisettling Flow Improving (HAFI) technology retards wax crystal growth while dispersing wax particles to prevent fuel filter plugging. The key is keeping the crystals that inevitably form from growing large and clumping together. Untreated mats of crystals are what stop the fuel from flowing and can be measured by the “Cold Filter Plug Point” test.

And if a lack of preparedness has led to fuel gelling in winter weather, Penray recommends the use of a winter thawing agent, which will dissolve gelled fuel. These are designed for emergency recovery use to get the vehicle back on the road and are not generally recommended for routine preventative use. There are many reasons for your customers to use appropriate diesel fuel additives with every fill-up, in both summer and winter weather conditions. Carefully crafted and tested additives can enhance cetane ratings for improved performance and cold starts, they can reduce the accumulation of sludge and other undesirable contaminants, they can add lubricity to protect internal engine components, and they can provide many of the benefits previously afforded by the now-diminished sulfur content of the fuel.

Such additives can also enhance the performance of the fuel filtration system, helping to separate water from fuel. Coalescing dispersed water can reduce the development of micro-organisms and failure rates of injectors and other components and, therefore, reduce down time and improve productivity. Explain it to your customers this way: While they don’t hesitate to take medicine or other “additives” when their bodies need supplemental help in order to function properly, they should treat diesel fuel systems with similar regard.   ●

Examples of diesel fuel and oil treatment manufacturers

Amsoil, (715) 399-8324,

Gold Eagle, 4400 S. Kildare Ave., Chicago, IL 60632, (800) 367-3245,

Lucas Oil, 302 North Sheridan St, Corona, CA  92880, (800) 342-2512,

Penray, 440 Denniston Ct., Wheeling, IL 60090-4731, (800) 323-6329,

Power Service, P.O. Box 1089, Weatherford, TX 76086, (800) 643-9089,

Prolong Super Lubricants, 1937 Mount Vernon Ave., Ponoma, CA 91768-3312, (800) 540-5823,

Red Line Synthetic Oil Corp., 6100 Egret Ct., Benicia, CA 94510, (707) 745-6100,

Rev-X Products, 4349 40th St., Grand Rapids, MI 49512, (616) 200-4335,

Schaeffer’s Fuel Additives, 102 Barton St., St. Louis, MO 63104, (800) 325-9962,

Sea Foam, 12987 Pioneer Trail, Eden Prairie, MN 55347, (952) 938-4811,

Stanadyne Corp., 92 Deerfield Rd., Windsor, CT 06095, (860) 525-0821,

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