Today, the heavy-duty diesel engine industry and OEMs are increasingly looking to fuel economy to reduce carbon emissions.

Why? Because 22.4 pounds of CO2 are emitted with every gallon of diesel fuel burned1, so the less fuel a vehicle uses, the less CO2 it emits.

The growing demand for improved fuel economy has, in turn, driven the adoption of low-viscosity diesel engine oils. That the viscosity of a lubricant can contribute to an engine’s fuel economy is well known within the industry.

But it has taken nearly a decade for many operators to transition from heavier viscosity oils to thinner ones due to habit, apprehension about the performance and protection, and sometimes the cost.

In general, lower-viscosity oils reduce the amount of energy required to keep engine components in motion, which lowers fuel consumption.

Shell Rotella

For example, switching from an SAE 15W-40 oil to an SAE 5W-30 oil could provide significant efficiency gains. Lowering fuel consumption of course lowers fuel costs, however, even if fuel costs are not a concern for a fleet or driver, lowering CO2 emissions may be.

The focus on engine oil viscosity offers greater opportunities to realize fuel efficiency and therefore reduce the total cost of ownership through lubricant choice. However, it’s not enough to evaluate new engine oils in the laboratory: the true test is how they protect vehicles in real-life conditions.

Strengthened by a long history of investigating the effects of lubricant viscosity on fuel economy, Shell has developed a multi-year global fuel-economy field trial program – in real trucks, on the road.

The results help everyone understand these opportunities in realistic, achievable numbers (read on to discover what fuel economy savings certain Shell Rotella oils offer). And our program has shown that switching to low-viscosity engine oils could help operators and drivers achieve significant efficiency gains.

Efficiency excellence

“Shell has accumulated more than 100 million miles in testing CK-4 and FA-4 type technologies, which show excellent engine protection in the field, even at low viscosities,” says Dan Arcy, Shell Global OEM Technical Manager, Heavy-Duty Diesel Engine Oil.


How we did it

Developing and testing new engine oils requires a careful balance: fuel economy must be balanced with product durability. And the precision of laboratory testing must be balanced with evaluating the oil’s performance in real-world conditions.

Consumers want to know that any performance benefits were tested and achieved under conditions that closely match their real operational conditions for the oil. However, evaluation in the field can be difficult because many factors influence real-world fuel economy, mainly driver behavior and driving conditions.

To isolate the effect of a lubricant, oil formulators conduct large-scale experiments that minimize the number of variables to be controlled, and standardize those variables that cannot be controlled. This approach eliminates bias and enables accurate evaluations of an oil's impact on fuel economy.


Delivery Truck

Urban and highway driving conditions

How you drive can play a big role in your fuel economy. For example, trucks with different duty cycles, such as urban start–stop or high-speed, long-distance highway driving, will have different efficiencies.

Shell uses the Society of Automotive Engineers industry-standard drive cycles designed to reflect different driving environments: J1321 and J1526. The field trial is designed using these standards.

rotell fuel economy canada

Statistics drive precision

Measurements are repeated and averaged, and the experiments carefully designed to minimize the variables that cannot be controlled, such as weather and humidity.


Standardized conditions

It’s important to isolate the impact of the lubricant itself. Shell’s experiments are run at certified independent test houses that regularly conduct closed-track experiments that simulate real-world driving conditions.

comparing oil

Comparing the right oils

Shell scientists tested six different development or prototype oils, including a reference CK-4 SAE 15W-40 oil and a prototype CK-4 SAE 5W-30 oil to understand their impact on fuel economy. Each truck saw each engine oil to ensure more accurate results.

rotella weighing

Measuring fuel economy

Fuel consumption is measured by weighing the fuel tanks before and after each test run, and using electronic data loggers from the vehicle control unit. The fuel-economy benefit is calculated relative to a reference lubricant:

Fuel saved (%) = Average fuel used (ref. lubricant) ÷ Average fuel used (test lubricant) x 100


                           Average fuel used (ref. lubricant)

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Engine technologies

A wide range of engine manufacturers and types of technology are selected so that the results are representative of what customers experience in the market. In this case, six vehicles from different manufacturers were chosen. In addition, the vehicles are matched according to mileage and condition.

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The program results

The Shell heavy-duty diesel engine oil technology team applied the above approach to fuel economy field trials in North America, China and Europe between 2014 and 2017. The results showed that lubricant selection has a significant impact on fuel economy in real-world driving conditions.

For example, compared with a market reference SAE 15W-40 oil, an SAE 10W-30 API FA-4 type oil resulted in a statistically significant fuel-economy benefit of up to 2.6% over the combined urban cycles. In other words, switching to a low-viscosity Shell engine oil could lead to a substantial reduction in fuel costs over time.

“We believe Shell to be the first organization to conduct a fuel economy trial of this scale and complexity. At its heart is a drive for the Shell technology team to deliver credible results to our customers using their equipment,” says Dr Jason R. Brown, Shell Heavy-Duty Diesel Engine Oil Global Technology Manager.

We know that going to a lighter/lower viscosity product like our Shell Rotella® T5 10W-30 Synthetic Blend or Shell Rotella T6 Multi-Vehicle 5W-30 Full Synthetic can provide significant fuel economy benefits.

Shell Rotella ranges

Which Shell Rotella products give better fuel economy?

Based on our extensive field trials

  • 2.8% fuel economy saving2: Shell Rotella T6 Multi-Vehicle 5W-30 Full Synthetic Oil
  • 2.6% fuel economy saving2: Shell Rotella T5 Ultra Synthetic blend 10W-30 (API FA-4) Oil
  • 2% fuel economy saving2: Shell Rotella T5 10W-30 Synthetic Blend Oil

“It’s well known that fuel economy links to CO2 emissions, so even if saving money on fuel isn’t a top priority, becoming greener may be” says Shell Rotella Global Manger, Megan Pino.

“Drivers, fleet owners and manufacturers alike are increasingly turning to engine oil as a way to enable and deliver fuel economy benefits. And we expect this trend to keep growing.”

1 According to the US Energy Information Administration.

2 Compared to a conventional SAE 15W-40 oil.

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