Understanding the Kenworth W990 Engine Options
February 12, 2026 - 8:43:18 am

The Kenworth W990 is more than just a truck; it is a statement. With its commanding long hood, traditional styling, and luxury interior, it is the modern successor to the legendary W900. But while the chrome and the curves catch the eye, it is what’s under that long hood that pays the bills.

Choosing the right engine for your W990 is the most critical decision you will make during the ordering process. It determines your fuel economy, your pulling power, your maintenance costs, and ultimately, your profitability.

At Wallwork Truck Center, we help owner-operators and fleet managers spec the perfect truck for their specific routes every day. Whether you are hauling heavy equipment through the Rockies or running refrigerated freight across the Plains, there is a specific engine configuration designed for you.

This guide breaks down the primary engine options for the Kenworth W990: the PACCAR MX Series and the Cummins X15.

1. The PACCAR MX-13: The Efficient All-Rounder

For many W990 owners, the proprietary PACCAR MX-13 is the "Goldilocks" engine—it offers the perfect balance of weight, power, and efficiency.

The Specs

• Displacement: 12.9 Liters
• Horsepower: 405 – 510 HP
• Torque: 1,450 – 1,850 lb-ft
• Dry Weight: ~2,600 lbs

Why Choose the MX-13?

1. Weight Savings:

The MX-13 is significantly lighter than its 15-liter competitors. In an industry where every pound counts, saving 400-500 lbs on the engine means you can legally haul more freight. Over the course of a year, that extra payload capacity translates directly to revenue.

2. Integrated Powertrain:

When you pair the MX-13 with the PACCAR TX-12 or TX-18 automated transmission and PACCAR axles, you get a fully integrated powertrain. The engine and transmission communicate seamlessly, resulting in smoother shifting and optimized fuel maps that adapt to the road terrain.

3. B10 Design Life:

The MX-13 is built with a B10 design life of one million miles. This means that 90% of these engines are expected to reach the million-mile mark without requiring a major overhaul.

Ideal For:

• Regional Haul
• Linehaul (OTR)
• Weight-Sensitive Bulk Hauling (Grain, Fuel)

2. The Cummins X15: The Heavy Hitter

If your motto is "There is no replacement for displacement," then the Cummins X15 is likely on your radar. As the industry's premier 15-liter big-bore engine, the X15 gives the W990 the muscle to handle the heaviest jobs on the road.

The X15 is generally available in two distinct series for the W990, depending on your needs:

A. The Productivity Series

Designed for vocational and heavy-haul applications where throttle response and raw power are non-negotiable.

• Horsepower: Up to 605 HP
• Torque: Up to 2,050 lb-ft
• Best For: Heavy Haul, Logging, Oil Field, Dump Trucks.

B. The Efficiency Series

Tuned specifically for down-speeding and maximum fuel economy while still providing 15-liter durability.

• Horsepower: 400 – 500 HP
• Torque: 1,450 – 1,850 lb-ft
• Best For: Long-Haul Fleets who prefer Cummins hardware but want to minimize fuel costs.

Why Choose the Cummins X15?

1. Massive Engine Braking:

The X15 features the most powerful engine brake in the industry. If you frequently descend steep grades (like the Rockies or the Appalachians) with heavy loads, the braking power of the X15 provides a massive safety advantage and saves wear on your service brakes.

2. Resale Value:

Historically, long-hood trucks like the W990 spec'd with a big-bore Cummins engine hold their value incredibly well. The secondary market loves this engine.

3. High Gross Combination Weights (GCW):

If you are hauling over 80,000 lbs—double trailers, heavy machinery, or oversized loads—the 2,050 lb-ft of torque available in the Performance/Productivity series is essential to get the load moving and keep it moving.

3. The PACCAR MX-11: The Specialist

While less common in a long-hood truck like the W990, the 10.8-liter PACCAR MX-11 is an option for very specific applications.

The Specs

• Displacement: 10.8 Liters
• Horsepower: Up to 430 HP
• Torque: Up to 1,650 lb-ft

Why Choose the MX-11?

The MX-11 is all about weight reduction. It is approximately 400 lbs lighter than the MX-13. If you are configuring a W990 as a regional dump truck, concrete mixer, or bulk hauler where you are paid strictly by the ton, the MX-11 allows you to maximize your payload. It provides ample power for local work while sipping fuel.

Comparison Table: At a Glance

Which Engine is Right for You?

Choosing between these engines often comes down to your daily operation.

• Choose the PACCAR MX-13 if: You run standard 80,000 lb loads OTR and want to maximize fuel efficiency and driver comfort with a quiet, smooth integrated powertrain.
• Choose the Cummins X15 if: You haul heavy (100k+ lbs), run in mountainous terrain, or simply demand the highest horsepower available for prestige and performance.
• Choose the PACCAR MX-11 if: You run a local vocational W990 and need every available pound for payload.

Let Wallwork Truck Center Help You Decide

Reading the specs is a good start, but driving them is the proof. At Wallwork Truck Center, we are experts in the Kenworth W990. We can simulate your specific route and load requirements to show you exactly how each engine will perform in the real world.

Don't guess on your investment. Contact our sales team today to discuss which engine will power your business forward.