Diesel vs Gas Fleet Trucks: Honest 2025 Cost Comparison

For decades, diesel powered trucks dominated every fleet spec sheet. The torque, durability, and reliability were unmatched — the gold standard for heavy-duty applications.

Every Class 5 or 6 order? Diesel. No questions asked.

But in 2025, the conversation around diesel vs gas trucks looks different. Gasoline engines have closed the gap in torque and fuel efficiency, while offering lower maintenance costs and easier service.

So this isn’t a pro-gas or anti-diesel piece. It’s a practical breakdown of what the data says — the real trucks pros and cons fleets are seeing in the field.

Real Fleet Cost Breakdown: Diesel vs Gas Fleet Trucks

🔍 Quick Tip: Search “diesel prices near me” before ordering your next chassis — local differences in diesel fuel pricing can swing your total ownership cost fast.

The gap between gas and diesel engines has narrowed. Diesel still wins on torque and resale, while gas powered trucks now edge ahead in uptime and cost control.

DEF Systems: Still the Wildcard

Ask any fleet manager about DEF and you’ll see the same reaction — eye roll first, story second.

Modern diesel powered engines rely on complex DEF and SCR systems to meet emissions standards. While reliability has improved since 2021, even a $2 sensor can still disable a $90,000 truck.

A balanced fleet strategy budgets for at least one DEF-related repair per vehicle life cycle.
On the flip side, gasoline engines avoid DEF altogether and use simpler emission controls, which means less downtime and fewer electronic failures.

Power vs ROI: Comparing Gas and Diesel Engines

This is where fleets compare diesel vs gas directly.

Diesel still offers stronger powered engines for low-RPM torque, PTOs, and towing. Gasoline power, however, gives better acceleration and higher horsepower for local or municipal routes.

The fuel economy difference used to favor diesel heavily — now it’s often within 1–2 MPG. With gas prices holding lower per gallon, the operational cost advantage can tilt toward gas trucks pros on short routes or moderate loads.

And when it comes to routine service, spark plugs and filters on gas trucks are cheaper than injectors and turbos on diesel units.

When Diesel Still Makes Sense

Diesel remains the right choice for:

• High-idle or PTO-driven fleets that run hydraulics or cranes all day

• Off-road or remote fueling where diesel fuel storage is safer

• High-mileage routes (20,000+ miles annually) where fuel efficiency offsets upfront cost

• Continuous heavy-duty use in towing or hauling

For these operations, diesel powered trucks still dominate. The torque curve, long-term durability, and fuel economy under load remain unmatched.

If uptime depends on torque, diesel is still the king.

When Gas Works Better

That doesn’t mean diesel is always smarter.

Gas powered fleets now perform impressively in low to medium duty cycles. Gasoline engines have evolved — higher compression ratios, improved transmissions, and lighter materials mean they’re no longer limited to “light-duty” work.

Fleets prefer gas for:

• Short routes under 50 miles/day

• Lower maintenance costs and faster repairs

• Urban environments with stop-and-go cycles

• Technicians who already service spark plug engines

In many cases, the ROI flips: lower purchase price + faster turnaround = faster payback period.

And for mixed fleets, the simplicity of managing gas and diesel engines side-by-side — without DEF supply or training issues — can be a major advantage.

Choosing between gas and diesel isn’t just about the engine — it’s about the upfit. The right body and equipment can completely change your truck’s ROI. Learn how expert vehicle upfitters transform plain chassis into profit-driven assets.

Download the Diesel vs Gas Upfit Comparison Chart

Want to see which powertrain fits each body type?
Download the full Diesel vs Gas Upfit Comparison Chart (PDF) below:

This chart compares:

• Hooklift, dump, mechanic, landscape, and refuse builds

• Idle-hour tolerance, fuel efficiency, and ROI

• How each performs under real heavy-duty conditions

For a full breakdown of what an upfit actually includes — from bodies to hydraulics — read What Is an Upfit on a Work Truck?. It covers costs, common mistakes, and how to calculate ROI for every spec.

Key Questions Before You Spec

Before ordering your next unit, ask:

• What’s our average idle time per shift?

• Do our routes truly need diesel torque?

• Can our shop handle gasoline and diesel engines equally well?

• What are our real maintenance costs per mile?

• Does our downtime erase any fuel economy advantage?

The answers will guide you better than brand loyalty ever will.

Once you’ve nailed your spec strategy, the next question is reliability. See which 2025 work trucks fleets actually trust to keep moving — from full-size pickups to heavy-duty municipal rigs.

Real Data Beats Old Habits

This debate isn’t about emotion — it’s about math.
Both gas and diesel engines can be profitable if used in the right application.

Diesel gives you torque, longevity, and stronger resale. Gas gives you lower costs, faster service, and flexibility.
Neither is perfect — both can wreck your budget if mis-spec’d.

The fleets winning in 2025 aren’t arguing.
They’re tracking fuel, hours, and uptime — and letting the numbers choose the spec.

🧠 Join and become a Founding Member of The Upfit Insider to get:

• Field-tested spec breakdowns

• ROI checklists and fleet tools

• Real stories from operators running both diesel vs gas trucks

—
Leyhan
Founder, The Upfit Insider