At the heart of any heavy-duty truck lies its diesel engine, a precision machine dependent on a carefully timed combustion process. If components like fuel injectors, glow plugs, or air filters are worn or malfunctioning, combustion becomes less efficient.
A diesel engine running rich (too much fuel) or lean (not enough fuel) burns more diesel than needed, which leads to excessive fuel consumption. Worse yet, improper combustion produces more soot, clogging the Diesel Particulate Filter (DPF) and initiating premature regenerations—a process that consumes even more fuel.
A faulty transmission doesn’t just affect drivability—it quietly saps fuel. Whether it's delayed shifting, slipping gears, or worn clutches, energy is lost during power transfer from the engine to the wheels. In automatic and Automated Manual Transmissions (AMTs), even minor electronic or hydraulic issues can increase resistance, forcing the engine to work harder.
Maintaining clean transmission fluid, ensuring proper torque converter function, and calibrating shift points through the ECM are all critical to preserving fuel economy.
Improper tire alignment and unbalanced wheels increase rolling resistance, forcing the engine to exert more torque to maintain speed. Misalignment not only increases fuel consumption by up to 10%, but it also causes uneven tire wear, shortening the lifespan of a costly asset.
Routine suspension inspections, including bushing wear and shock absorber effectiveness, are essential for keeping alignment in spec and improving fuel economy.
Brake drag is an often-overlooked factor in fleet fuel efficiency. Faulty slack adjusters, improperly adjusted S-cams, or stuck brake shoes can cause subtle, ongoing resistance during normal driving.
When brakes don’t fully disengage, the engine must overcome this resistance, reducing miles per gallon. Frequent inspections of air brake systems are necessary, including the:
The driveline connects the transmission to the wheels—and every inch of it matters. Worn U-joints, damaged differentials, or misaligned driveshafts cause power loss and unnecessary fuel burn.
Additionally, a misfunctioning locking differential or limited-slip differential can result in uneven power distribution, especially under load, which increases fuel consumption. Ensuring that differential gearing is properly lubricated and sealed prevents friction-related inefficiencies.
An engine that runs hot runs inefficiently. Blocked radiators, faulty fan clutches, or failing water pumps cause the engine to operate above ideal temperatures, which reduces combustion efficiency.
Additionally, transmission coolers and oil coolers that aren’t performing well lead to increased thermal load on the engine and gearbox, further taxing fuel consumption. Regular coolant flushes and inspections help avoid these costly inefficiencies.
If the DPF, SCR system, or EGR valve is malfunctioning or overdue for cleaning, your truck could enter a derate or regeneration cycle more frequently. Every regeneration burns extra diesel. Worse yet, DEF system issues may cause derates that limit speed and increase idle time.
Frequent forced regenerations and clogged filters are often symptoms of upstream engine problems—poor fuel spray patterns, inefficient combustion, or excessive soot production. Addressing root causes through thorough diagnostics is key.
Preventive maintenance is far more than a checklist—it’s the backbone of fleet fuel efficiency. By catching problems early, fleets avoid the compounding fuel waste caused by neglected systems.
Key preventive tasks include:
Many of these tasks can be handled through mobile fleet service, reducing downtime and increasing inspection frequency.
ECM tuning allows fleets to recalibrate engine performance parameters, including:
While performance tunes increase power at the cost of efficiency, economy-focused tuning reduces fuel use by optimizing combustion timing and reducing engine strain under partial load. However, improper tuning can void warranties and lead to compliance issues, so it should always be conducted by qualified professionals.
Fleet-wide fuel efficiency doesn’t happen by accident. It is the direct result of well-maintained systems, proactive repair practices, and a data-driven approach to equipment performance. From the engine bay to the axle shafts, every moving part has a role in determining how far your trucks go on a gallon of diesel.
For fleets operating in and around Phoenix, Onsite Truck & Equipment Repair offers the technical expertise to keep your systems dialed in and your fuel usage down.
