Fuel isn’t just a line item—it’s one of the biggest costs in fleet operations. And while there’s no controlling pump prices, there is something fleet managers can control: how efficiently their vehicles use every gallon.

That’s where lubricant selection comes in. Many fleets overlook the role of engine oil, grease, and transmission fluid in fuel consumption. But the right premium lubricants can help reduce internal friction, improve engine performance, and minimize the energy lost to heat and resistance.

Small percentage gains in fuel economy add up quickly across a large fleet. Let’s take a closer look at how—and where—those savings show up.

The Hidden Cost of Conventional Lubricants

For years, 15W-40 mineral oils were the industry standard for heavy-duty diesel engines. They got the job done—but at a cost most fleets didn’t fully recognize. Conventional lubricants generate more internal friction, resist flow in colder conditions, and break down more quickly under heat and load. All of that forces the engine to work harder—and burn more fuel in the process.

This isn’t just theory. Field tests and fleet trials consistently show that conventional engine oils lead to higher fuel consumption, particularly in long-haul or high-load conditions. The difference between a conventional 15W-40 and a synthetic 10W-30 FA-4 oil may seem small on paper, but in real-world operation, that viscosity shift alone can translate to measurable gains in efficiency.

Conventional oils also tend to require more frequent changes. That not only adds maintenance labor and downtime—it also means the engine spends more of its life running on degraded oil, further cutting into fuel economy and performance.

In the end, sticking with conventional lubricants could be quietly costing your fleet thousands of dollars a year in wasted fuel and avoidable wear. Making the move to full synthetic is no longer about early adoption—it’s about staying competitive.

Why Full Synthetic Pays Off at the Pump

Synthetic lubricants don’t just last longer—they help your engines run leaner. By reducing internal friction and resisting breakdown under stress, full synthetics like Mobil Delvac™ 1 and Extreme FE allow more of the fuel’s energy to go toward moving the vehicle, not overcoming resistance inside the engine.

This efficiency is built into the chemistry. Synthetics are formulated with uniformly sized base oil molecules that flow more easily, maintain stability at higher temperatures, and reduce drag in moving parts. That translates directly into improved combustion efficiency and less wasted energy.

Fleets running Mobil Delvac™ synthetics have reported fuel economy gains of up to 2%. That figure isn’t a lab projection—it’s been measured in real-world operations. According to Mobil, one Chicago-based fleet documented $125,000 in annual savings after switching to Mobil Delvac™ Extreme 10W-30. Another saw a 1% improvement in fuel economy across their fleet, cutting fuel usage while extending drain intervals to 90,000 miles.

Even modest fuel savings add up quickly when multiplied across dozens—or hundreds—of vehicles. For most fleets, synthetic oil starts paying for itself long before the next scheduled oil change.

Beyond the Engine: Fuel-Saving Lubricants Across the Powertrain

Engine oil may get most of the attention, but it’s not the only lubricant that affects fuel efficiency. Every part of the drivetrain—from the transmission to the axles to the wheel ends—creates drag. The more efficiently those components move, the less fuel your fleet burns.

Mobil Delvac’s bumper-to-bumper synthetic solutions are designed to reduce parasitic losses across the entire powertrain. That means lower rolling resistance, smoother shifting, and better thermal stability under load—all of which contribute to real-world fuel savings.

Here’s how it adds up:

Transmission Fluids: Mobil Delvac 1™ ATF and TES 668 fluids reduce internal friction, support faster shift response, and maintain viscosity under high heat—ideal for modern automatic and automated manual transmissions.
Gear Oils: Mobil Delvac 1™ Gear Oil 75W-90 lowers churning losses in differentials and axles, helping reduce power loss while protecting against wear under heavy loads.
Greases: Low-friction greases like Mobil Delvac™ Xtreme Grease minimize drag in wheel-end applications and chassis components. They also resist water washout, which helps maintain consistent lubrication and extend service intervals.

When these systems are all optimized together, the impact on fuel economy is no longer marginal—it becomes a measurable advantage across every mile.

Choosing the Right Synthetic for Your Fleet

Not all synthetic oils are the same—and not every fleet has the same needs. Mobil Delvac™ offers a range of premium synthetic lubricants designed to meet different operating conditions, budgets, and fuel economy goals.

Here’s how the most widely used options compare:

Mobil Delvac 1™ Advanced Fuel Economy (5W-30 FA-4)
This full synthetic is engineered for the latest fuel-efficient diesel engines requiring FA-4 oils. It offers excellent cold-start performance, high-temperature stability, and industry-leading fuel economy potential.
Best for: Fleets running newer engines that support FA-4 specifications and are looking to maximize MPG gains.

Mobil Delvac™ Extreme FE (10W-30 FA-4)
A full synthetic that balances wear protection with improved fuel economy. It’s optimized for extended drain intervals and high-load applications.
Best for: Fleets looking to upgrade from 15W-40 to a more efficient option without compromising protection.

Mobil Delvac™ Super FE (10W-30 FA-4)
A synthetic blend that delivers solid performance and improved fuel economy over conventional oils, while being more budget-friendly than full synthetics.
Best for: Fleets seeking a cost-effective entry point into fuel-efficient lubricants—particularly in regional or mixed-duty operations.

Each of these oils is backward-compatible with specific OEM engine models, but it's essential to check compatibility—especially when moving to FA-4 oils. GPI can help you evaluate your fleet, your current service intervals, and your fuel goals to match you with the right product for your equipment mix.

Transitioning to Full Synthetic: What Fleet Managers Need to Know

Making the move to synthetic lubricants isn’t complicated—but it does require a plan. For many fleets, the biggest gains come when the transition is part of a broader maintenance strategy, not just a one-off change at the next oil service.

Here’s what to keep in mind:

Check OEM compatibility. Most newer engines support FA-4 oils like Mobil Delvac™ 1 and Extreme FE—but always confirm before switching.
Start with your highest-mileage or most fuel-hungry assets. These vehicles offer the quickest return on investment. Early wins can help justify a fleet-wide shift.
Use oil analysis to optimize drain intervals. Regular sampling ensures you’re getting the full value from your synthetic investment without sacrificing protection.
Consider full powertrain integration. Transmission fluids, gear oils, and greases all contribute to efficiency. The biggest savings come when everything’s working together.
Work with a trusted partner. Choosing the right lubricant isn’t just about the spec sheet—it’s about how it performs in your specific operation. GPI can help you make the transition with confidence.

Even partial upgrades can yield measurable results. But when a fleet commits to high-efficiency synthetics across the board, the long-term savings are hard to ignore.

The Bottom Line: Fuel Savings That Add Up

Fuel efficiency isn’t just about the engine—it’s about the strategy behind the oil you choose. Full synthetic lubricants like Mobil Delvac™ 1 Advanced Fuel Economy, Extreme FE, and Super FE reduce internal friction, extend drain intervals, and deliver measurable savings across the life of your fleet.

Now’s a great time to make the switch. With the Mobil Fleet Uptime Program, qualifying fleets can receive up to $2,000 in free oil analysis services through Mobil Serv℠—giving you data-backed insights that help extend oil life, reduce unplanned downtime, and maximize performance.

Want to learn more? Contact GPI today to find the right Mobil Delvac™ products for your fleet—and take advantage of this promotion while it lasts.