The Ultimate Buyer’s Checklist: Inspecting a Pre-Owned Cat 320D

In the world of heavy construction equipment, few machines hold a reputation as solid as the Caterpillar 320D. Known for its durability, fuel efficiency, and versatility in the 20-ton class, it is a staple on job sites ranging from road construction to mining. However, the difference between a profitable investment and a money pit often lies in the condition of the specific unit you choose to purchase.

Acquiring heavy equipment is a significant capital expenditure. While a brand-new machine offers peace of mind, it comes with a premium price tag. Consequently, many contractors turn to the secondary market. When searching for a Pre-Owned Cat 320D, the potential for high value is immense, provided you know exactly what to look for. This guide serves as your professional roadmap to evaluating the condition of a used excavator, ensuring that your next purchase is ready to work from day one.

1. The Paperwork and History Check

Before you even kick a tire or check the oil, the inspection begins with documentation. A well-maintained machine leaves a paper trail. Ask the seller for the full service history. You want to see proof of regular maintenance intervals, particularly for oil changes and hydraulic filter replacements.

Verify the serial number plate on the machine and match it with the paperwork. Check if the Serial Number implies where the machine was manufactured, as this can sometimes affect parts availability or specifications. Additionally, validate the hour meter reading against the wear and tear visible on the pedals and joysticks. If the pedals are worn through but the meter says 2,000 hours, the meter has likely been tampered with or replaced.

2. Undercarriage: The High-Cost Component

The undercarriage of a tracked excavator represents approximately 50% of the machine’s total repair and maintenance costs over its lifespan. Therefore, this should be the first area of your physical inspection.

Start by looking at the tracks. Are they sitting squarely on the rollers? Inspect the track shoes (grouser plates) for wear. If the grousers are rounded or worn down significantly, traction will be compromised.

Move on to the links and pins. Check for “snake” wear on the chains, which indicates the internal pins are worn out. Inspect the sprockets; the teeth should not be sharp or pointed. Pointed teeth indicate the sprocket has reached the end of its life. Similarly, check the idlers and bottom rollers for leaks or flat spots. A quick tip is to touch the rollers after a test run (carefully)—excessive heat can indicate bearing failure.

3. Structural Integrity: Boom, Stick, and Bucket

The heavy lifting takes a toll on the steel structure. Inspect the boom and stick for any cracks, particularly near the welding points. Cracks here are major red flags that suggest the machine was abused or used for tasks beyond its capacity, such as hammering rock without proper technique.

Examine the bucket teeth and side cutters. While these are wear parts and easily replaceable, a bucket in poor condition might indicate a lack of general care. More importantly, check the play in the bucket pins and bushings. There should be minimal movement. If the bucket wobbles significantly when lifted and shaken, you are looking at an immediate repair bill for line boring and pin replacement.

The process of buying used machinery requires a keen eye for these structural details, as welding repairs on high-stress areas like the boom root are expensive and can devalue the machine if done poorly.

4. The Heart of the Beast: Engine Inspection

The Cat 320D is typically powered by the robust Cat C6.4 ACERT engine. When inspecting the engine, start with a cold check. Ensure the engine has not been pre-warmed by the seller, as a warm engine can hide starting issues.

Check the oil levels and the condition of the oil. It should not be milky (indicating water/coolant mixing) or smell burnt. Look for blow-by, which is pressure escaping past the piston rings. You can check this by removing the oil filler cap while the engine is running; a steady stream of smoke indicates worn rings or liners.

Pay attention to exhaust smoke:
Blue smoke typically indicates burning oil.
White smoke can indicate coolant burning or fuel injection issues.
Black smoke usually points to air-to-fuel ratio problems, often a dirty air filter or failing injectors.

Inspect the radiator and cooling system hoses. Brittle or cracking hoses are a sign of age and heat exposure. Also, look for any signs of fuel leaks around the injectors, a critical check for the 320D model.

5. Hydraulics: Power and Precision

The hydraulic system is the lifeblood of an excavator. A weak pump means a weak machine. Inspect all cylinders (boom, stick, bucket) for chrome pitting or scoring on the rods. Even small scratches can damage the seals and cause leaks.

Check the hydraulic pump compartment. It should be relatively clean and dry. Any signs of hydraulic fluid spraying or dripping are concerns.

Perform a load test if possible. Listen to the hydraulic pump as you operate the machine. It should not whine excessively or make grinding noises. A critical test is to maximize the cylinders (bottom them out) and listen to the relief valves. The engine should load down slightly but should not stall. If the engine dies when you engage the hydraulics, there is a mismatch between the engine power and hydraulic demand, often pointing to pump issues.

6. The Swing Bearing (Slewing Ring)

The swing bearing is one of the most expensive single components to replace. To check this, position the upper structure 90 degrees to the tracks. Lower the bucket to the ground and use the boom to lift the tracks slightly off the ground. Then, try to gently rock the machine.

You are looking for play or movement between the upper structure (house) and the undercarriage. Excessive play indicates the swing bearing is worn. Also, rotate the cab a full 360 degrees. The movement should be smooth without any “notches,” grinding noises, or hesitation.

7. Cab and Controls

Finally, climb into the operator’s seat. The condition of the cab often reflects how the operator treated the machine. Is the seat torn? Are the windows cracked?

Start the machine and check the monitor panel. Ensure there are no error codes displayed. Test the air conditioning and heating—essential for operator comfort and productivity. Check the travel levers and joystick controls. They should return to neutral automatically and move smoothly.

8. Putting It All Together

After the physical walkthrough, it is vital to operate the machine. Dig a hole, lift a load, and travel up a slope. Does the machine track straight? Does it have the power to lift the boom while tracking?

Follow this comprehensive excavator inspection checklist to ensure you aren’t missing any critical systems. If you are not mechanically inclined, it is highly recommended to hire a third-party heavy equipment mechanic to perform this inspection for you. They can perform fluid analysis (SOS) which gives an X-ray view of the internal wear of the engine and transmission.

Summary

Investing in a used Caterpillar 320D is a smart business move that balances performance with cost-efficiency. However, the reliability of the machine depends entirely on its maintenance history and current condition. By systematically inspecting the undercarriage, structural welds, engine health, and hydraulic performance, you can mitigate the risks associated with second-hand equipment. A thorough inspection today prevents costly downtime tomorrow, ensuring your excavator remains a profitable asset for years to come.