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How to Improve Fuel Economy in Diesel Engines

Featured image for "How to Improve Fuel Economy in Diesel Engines" blog post. Fleet of diesel trucks.

When looking at the operating budget of diesel fleets and trucking companies, the singular item that stands out in terms of being the biggest consumable expense would be diesel fuel. It is imperative to find as many ways as possible to lower the operating expenses for diesel fuel. Both truck manufacturers and diesel engine manufacturers agree that there are common rules to follow when trying to control fuel consumption costs. Specifically, we’ll try to address how to improve fuel economy in diesel engines by applying some simple, yet powerful strategies.

One of the culprits that can cause inefficient diesel engine operation and a cut down on fuel economy would be any issues relating to fuel injectors. Most OEM diesel equipment manufacturers understand that today’s modern diesel fuels are causing increases in fuel injector issues. A typical injector problem from the past was deposits forming on the tips of injectors. Currently, these deposits are now being found internally. Whether the problems are external or internal on fuel injectors, both will lead to reduced fuel economy, a lack of engine performance, less power, and injector life being diminished.

Modern internal diesel engine.
A high-performance diesel fuel additive will keep injectors clean, maximizing fuel economy.







How to Improve Fuel Economy in Diesel Engines

One simple strategy to implement is to choose a high-performance fuel injector fuel conditioner and cleaner. Looking for a diesel fuel additive that has a robust and heavy-duty additive package, along with a special lubricity agent, should help in cleaning up and removing harmful and fuel-robbing deposits by returning fuel injector tips to their original condition. The injector tips should now be able to create the proper atomized spray pattern.

By treating your diesel fuel consistently with a high-performance diesel fuel conditioner and cleaner, you should notice an increase in fuel economy. Specifically, there are some niche specialized lubricant manufacturers that offer improved fuel economy up to 6.5% while utilizing their diesel fuel additive.

The next recommended strategy that is quite easy to implement, yet can bring long-term benefits to your diesel engine, would be choosing the proper fuel mileage-improving motor oil. There are two choices when considering which type of motor oil to choose. Those two choices are conventional petroleum-based or synthetic. There are benefits to both if they are blended with high-quality base stocks and superior additive packages. It is possible for both types of motor oils to increase fuel economy. Still, for the sake of this blog post, we’re interested in maximizing fuel economy potential. With that in mind, the clear winner would be synthetic engine oils.

5W30 synthetic motor oil.
Heavy-duty synthetic motor oil reduces friction, leading to reduced fuel consumption.










Benefits of Synthetic Engine Oil

The first reason is the difference in molecular structure between petroleum-based engine oils and synthetics. The molecular structure of petroleum base oils is irregular. In simple terms, the fluid flow of such oils is uneven and tends to create unnecessary fluid friction. Additionally, during cold starts and cold weather, these irregular-sized molecules can thicken and flow much slower and with more resistance, leading to wasteful burning of the fuel.

On the flip side, synthetic base oils are manmade and designed with molecules of all the same size. Synthetic base oils provide a fluid flow that is smooth, quick flowing, and reduces friction. During cold starts and cold weather, their molecules do not increase in size or thicken, but rather flow rapidly and do not waste unnecessary fuel.

Massey Ferguson tractor.
Choosing a diesel engine oil made with high-quality base oils and a superior additive package will lead to a reduction in downtime.








Now that synthetic engine oils are the choice for how to improve fuel economy in diesel engines, let’s dig a little deeper into which specific synthetic motor oil can bring the greatest improvement in fuel economy. When a lubrication chemist is looking to formulate a fuel savings diesel motor oil, there are a few additives to consider. First would be the choice of a friction modifying additive.

As the name implies, its function is to reduce friction between two metals surfaces. By reducing friction, the engine is required to utilize less energy, which translates to having to burn less fuel. Depending on how far the chemist is willing to go when formulating an engine oil, he may add another additive to help in further decreasing fuel consumption.

There is one unique additive available with a long history in reducing friction and fuel consumption in all types of engines. That additive is known as molybdenum disulfide, or moly. Moly has a long history in offering a reduction in friction, which leads to fuel economy improvements. Also, moly is an excellent anti-wear protection agent.

Magnified image of molybdenum disulfide.
Molybdenum disulfide (MoS2) or moly is a friction-reducing additive and helps improve fuel economy.










The next area to consider when choosing the best synthetic-based motor oil would be viscosity. Many off-highway and on-highway diesel engines are required to run in a vast range of temperatures and conditions. Conventional diesel engine wisdom sees most engine users typically running a 15W40 CJ-4 engine oil. If your intention is to maximize your fuel economy, there is a better choice for a viscosity. By utilizing a moly 5W40 engine oil blended with synthetic base oils, tests have shown an increase in fuel economy of 1% to 3% in comparison to a conventional petroleum 15W40 CJ-4 engine oil. For all the reasons stated above, it is easy to see how this choice would lower fuel costs.

Extra Factors to Consider

Even though this blog post was specifically about how to improve fuel economy in diesel engines, we’d like to add a few other fuel mileage-improving tips. In addition to utilizing a moly-based engine oil, adding a moly-based gear oil for both transmission and rear end will help reduce friction and contribute to your fuel improving goals. The speed that you drive definitely impacts fuel economy. 55 mph seems to be the optimum speed for maximizing fuel efficiency.

Rt. 61 sign with a 55 speed limit sign.
55 mph seems to deliver the best fuel economy for over-the-road trucks.







Next, tires can dramatically affect fuel consumption. A brand new tire can cut your fuel economy by as much as 7% until they’ve been properly broken in. For every 10 psi that your tire is under-inflated, you may lose up to 1% fuel efficiency.

Semi truck tires.
Maintaining the correct tire air pressure contributes to improving fuel economy.







Another area that can reduce fuel economy is revving your engine too much. It is best to shift to the next gear slower than normal. Unnecessary idling, though necessary for certain periods of time, can be costly. Whenever possible, use shore power, or truck-stop electrification, rather than idling. Statistics have shown that a diesel operator can save up to $3,000 a year in diesel fuel costs by plugging in rather than idling.

Shore power stop.
Whenever possible, use shore power or truck stop electrification instead of idling for maximum fuel economy.








Hopefully, we’ve provided some food for thought on how to improve fuel economy in diesel engines.