Fuel efficiency issues can be some of the most aggravating (and costly) problems you’ll ever experience with your diesel truck.
Wasted diesel? It’s money right out of your pocket. Fuel represents such a large portion of most trucking business’ operating expenses that even slight improvements to your diesel mileage can make a big impact on your bottom line.
Fortunately, most common causes of poor diesel fuel economy are completely preventable. Whether it’s worn out truck components like a failing high pressure fuel pump or poor driving habits that sneak up on you… there are solutions to help fix them.
Let’s dive into the most common causes of diesel fuel economy issues and how to fix them!
What You’ll Learn:
- The Top Reasons Diesel Trucks Lose Mileage
- Driving Habits That Kill Diesel Fuel Economy
- High Pressure Fuel Pump & Fuel System Problems
- Simple Fixes to Improve Your Diesel Mileage
Fuel Economy is More Important Than Ever
Fuel really is the largest expense for most diesel trucks.
Not even close either. According to this recent article, fuel was 28% of overall carrier operating costs in 2022. That’s almost one third of every dollar going towards something other than actually running your business.
When fuel efficiency starts to slip, those costs quickly grow. What’s worse is truck owners often don’t realise their trucks are performing poorly until the damage is done.
Where it all Begins: The Fuel System
Your trucks diesel fuel system is where the power comes from. If your fuel system is compromised in any way, it’ll dramatically reduce your fuel efficiency.
Let’s take a look at a few of the big ones…
High Pressure Fuel Pump & Fuel System Weak Links
The high pressure fuel pump is a critical component of any diesel engine. Fuel pumps are responsible for delivering fuel at the correct pressure required for combustion. When your fuel pump goes into failure, fuel delivery becomes inconsistent and your engine has to work harder to try and maintain that level of power.
More fuel burned. For the same amount of power.
Some of the most common problems that lead to a failing high pressure fuel pump include:
- Worn out internal components
- Contaminated fuel
- Fuel pump wear from excessive mileage
These things happen gradually so sometimes your truck won’t show signs of decreased fuel economy until the problem has gone too far.
Outside of your high pressure fuel pump there are other fuel system components that can cause big losses in fuel economy. Dirty or clogged fuel filters limit the flow of fuel to your engine. Dirty or worn injectors spray an uneven mist which leads to uneven combustion. If you drive trucks with Volvo diesel engines, making sure you’re working with a reputable supplier for injection pumps for Volvo engines is always the best place to start.
The bottom line is this: Your fuel system has to be in good shape if you want to maintain good fuel economy. If your fuel system is dirty or failing… nothing else you do will matter.
Driving Habits That Slash Fuel Economy
Some of these statistics are hard to believe at first.
How you operate your truck has a HUGE impact on your fuel economy.
According to the American Trucking Associations, trucks traveling at 75 mph use 27% more fuel than the exact same truck traveling 65 mph. They’re running the same route. Carrying the same load. Everything is identical except speed.
That’s a staggering difference.
But speed is just the tip of the iceberg when it comes to bad driving habits. A few others that you might not know are:
- Idling too much: Did you know that an idling heavy duty diesel engine burns through about 0.8 gallons of fuel PER HOUR? That adds up when you stop at those long rest stops.
- Accelerating too quickly: Smoother acceleration means less fuel burned. Quick throttle inputs cause your engine to burn more fuel than necessary.
- Poor route planning: Running inefficient routes or through congested areas will burn more fuel than needed.
Solution? Be aware of how you drive. Keep a consistent speed when possible and utilize cruise control. If you can eliminate extra idling you’ll see a big difference at the pump.
Neglecting Maintenance
Another area that truck owners often neglect is maintenance. Regular maintenance is your best defense against falling fuel economy.
How does skipping maintenance affect your fuel economy? Simple. Your engine has to work harder.
A dirty air filter limits the amount of air flowing into the engine. The engine compensates by burning more fuel. A worn turbo won’t provide enough boost pressure. The engine compensates by burning more fuel.
It’s a cycle that repeats itself with each maintenance item that gets neglected.
Here are the maintenance related items that affect diesel mileage the most:
Air filters. These should be replaced every 15,000 to 30,000 miles. A dirty air filter will decrease your fuel efficiency.
Fuel filters. Fuel filters get replaced every 10,000 to 25,000 miles. When they get clogged up it restricts the flow of clean fuel to your high pressure fuel pump and injectors.
Tyre pressure. Rolling resistance is increased with under inflated tyres. Your engine has to work harder which reduces your fuel efficiency. Check your tyre pressure frequently.
Engine oil. Using the proper grade of engine oil and changing it at regular intervals reduces friction inside the engine and allows it to run smoothly.
Weight and Aerodynamics
People often overlook just how much weight and aerodynamics can affect fuel efficiency.
For every extra 100lbs on your truck you lose fuel efficiency. It doesn’t sound like much either but when you start adding that weight up over hundreds (or thousands) of miles it all adds up. Make sure you’re taking any unnecessary weight off your truck.
Aerodynamics play a big role too. As your speed increases, air resistance increases exponentially. Adding roof fairings, side skirts and trailer tails can all help reduce drag and improve your fuel efficiency.
Emissions System Malfunctions
Diesel trucks these days are equipped with all kinds of emissions equipment. Computers, sensors and emissions traps like the DPF and EGR are all meant to help reduce emissions. But when they go into failure, fuel economy takes a hit.
A plugged DPF causes your engine to go into regeneration much more frequently than it needs to. Regen burns fuel. A faulty EGR valve will cause incomplete combustion and your engine to burn more fuel.
Simple Fixes to Improve Fuel Economy
As you can see, there are a lot of reasons that fuel economy can go south in a diesel truck. Some of the most common issues are:
- A worn or failing high pressure fuel pump
- Bad driving habits (speeding, too much idling)
- Neglected Maintenance (air filters, fuel filters, tyre pressure, oil)
- Being overweight and/or poor aerodynamics
- Malfunctioning emissions equipment
The biggest take away from all of this? Problems with fuel economy can be prevented!
As mentioned above, start with the fuel system. Make sure your high pressure fuel pump, fuel injectors and filters are in good working condition.
Then tackle the driving habits and maintenance schedules.
Small improvements in each of these categories will equal BIG gains on your fuel bill.