Top 5 Things to Inspect When Buying Used Kenworth Trucks
December 18, 2025 - 8:21:06 am

For independent owner-operators and fleet managers alike, a Kenworth truck represents more than just transportation; it represents a legacy of reliability, durability, and American craftsmanship. Buying a pre-owned model is often a brilliant financial strategy, allowing you to acquire a premium Class 8 vehicle without the premium price tag of a new unit. However, the difference between a profitable investment and a maintenance nightmare lies in the inspection.

When searching for used Kenworth trucks, you need to look beyond the shiny paint and the chrome bumper. You need to understand the mechanical history of the machine.

At Wallwork Truck Center, we inspect thousands of trucks. We know exactly where the wear points are and what separates a "road-ready" rig from a fixer-upper. To help you make the smartest purchase decision, we have compiled this expert checklist of the top five critical areas to inspect before you sign on the dotted line.

1. The Engine: Assessing the Heart of the Beast

Whether the truck is powered by the efficient PACCAR MX-13 or the legendary Cummins X15, the engine is the single most expensive component to repair. A visual inspection and a cold start are non-negotiable.

• The Cold Start: Ask the dealer not to warm up the truck before you arrive. You want to start the engine "cold." Watch the exhaust stack immediately upon ignition. A puff of black smoke is normal, but persistent blue smoke (burning oil) or white smoke (coolant leak or injector issue) after the engine warms up is a red flag.
• Check for "Blow-By": Once the engine is running and up to operating temperature, remove the oil filler cap. If there is a significant amount of pressure or "puffing" coming out, it indicates worn piston rings or cylinder liners. A healthy engine should have minimal blow-by.
• Fluid Analysis: Visual checks have limits. We highly recommend asking for an oil analysis. This scientific test can detect microscopic metal particles (indicating bearing wear), coolant in the oil (EGR cooler or head gasket failure), or fuel dilution. It is the only way to see inside the engine without taking it apart.
• Turbo and Manifold: Inspect the turbocharger for oil leaks on the compressor side. Look for soot trails around the exhaust manifold, which indicate gasket leaks that can rob you of boost and fuel economy.

2. The Transmission: Ensuring Smooth Power Delivery

Kenworth trucks are renowned for their drivability, but a worn transmission can ruin that experience. Whether you are looking at an Eaton Fuller manual or a PACCAR automated transmission, the inspection is critical.

• Manual Transmissions:
• Clutch Brake: Test the clutch brake by depressing the pedal all the way to the floor. It should stop the input shaft and allow you to shift into gear without grinding.
• Synchronizers: On a test drive, float the gears (if you are experienced) or double-clutch. If the transmission grinds or pops out of gear under load, you may be looking at a costly rebuild.
• Automated Transmissions:
• Shift Logic: During the test drive, pay attention to the shift points. Does it hesitate? Does it "hunt" for gears on a slight incline? Jerky engagement at low speeds can indicate issues with the clutch actuator or the xy-shifter.
• Air Leaks: Many automated manuals rely on air pressure to shift. Listen for air leaks around the transmission housing, as a drop in air pressure can leave you stranded in neutral.

3. The Frame and Suspension: The Backbone of the Truck

The structural integrity of used Kenworth trucks is paramount. You are buying this truck to haul heavy loads, and the frame rails must be up to the task.

• Frame Rails: Inspect the entire length of the frame rails. You are looking for cracks, specifically around the suspension hangers and crossmembers. Be very wary of "fish-plating" (welded metal patches) on the frame, as this indicates a previous structural failure. Also, check for severe rust "jacking" between the frame rail and the crossmembers, which can weaken the chassis.
• Suspension Bushings: On Kenworth’s AG400L or AG460 suspensions, check the torque rods and spring bushings. If the rubber is cracked or missing, the axle alignment will be off, leading to rapid tire wear.
• Air Bags: Look for dry rot or cracks in the rubber of the air bags. A blown air bag under a heavy load is a safety hazard and an immediate breakdown.

4. Tires, Wheels, and Brakes: Where the Rubber Meets the Road

Tires are one of your highest recurring operating costs. The condition of the rubber on a used truck tells a story about how the previous owner maintained the vehicle.

• Tread Wear Patterns: Don't just check the depth; check the pattern.
• Cupping: Often indicates worn shocks or suspension issues.
• Inner/Outer Wear: Usually points to an alignment problem or worn kingpins.
• Wheel Condition: Inspect the wheels for cracks, especially around the lug nut holes and the hand-holes. If the truck has aluminum wheels, check for oxidation that can hide cracks.
• Brake Life: Check the thickness of the brake shoes or pads. If they are under 25%, factor the cost of a brake job into your offer. Also, inspect the S-cams and slack adjusters for excessive play.

5. Maintenance Records and ECM History: The Paper Trail

The most honest part of any truck is its paperwork. A well-maintained Kenworth will have a history that documents its care.

• The Paper Trail: Ask to see the maintenance records. consistently hit oil change intervals? Have the DPF (Diesel Particulate Filter) and DEF system been serviced or cleaned recently? A truck with gaps in its service history is a gamble.
• ECM Data: The Engine Control Module (ECM) records everything. Ask the dealer to plug in and show you the lifetime fuel economy, idle time, and any "hard braking" events. High idle time (over 30-40%) suggests the engine has more wear than the odometer indicates.
• Major Repairs: verifying if major components like the turbo, DPF filter, or clutch have already been replaced can save you thousands. If these original parts are still on a high-mileage truck, be prepared to replace them soon.

Buy with Confidence at Wallwork Truck Center

Inspecting used Kenworth trucks requires a keen eye and attention to detail. While this checklist empowers you to spot red flags, the safest way to buy is to partner with a dealer who has already done the hard work for you.

At Wallwork Truck Center, we put our used inventory through a rigorous inspection process before it ever hits the lot. We check the engine, test the transmission, and verify the history so that you can drive away with confidence.

Ready to find your next rig?

Browse our certified inventory of used Kenworth trucks online or visit us today to speak with our sales experts. Let us show you the maintenance history and let you take a test drive to feel the Wallwork difference.