Hydraulic Excavator Inspection Guide: What to Check Before You Buy

This guide walks through every system to inspect, in order. Bring it with you and work through it item by item. If something does not pass, you have leverage to negotiate or a reason to walk away.

If you have not read our used hydraulic excavator buying guide yet, start there. This article goes deeper on the inspection step.

Before You Start

A few ground rules. Once this machine is yours, it has to meet the same equipment safety standards OSHA holds every jobsite to. Inspect it now with that bar in mind, under OSHA’s general duty to inspect equipment and pull unsafe machines from service (opens in a new tab):

System 1: Hydraulic System

Start here. Hydraulic repairs are the most common major expense on used excavators, and many problems show up before you start the engine. This guide to hydraulic safety (opens in a new tab) covers the risks these systems carry under pressure.

Machine off

• Look for oil on the ground, hoses, the pump compartment, and the cylinders.
• Check the dipstick or sight glass. Clean fluid is amber or light brown; dark, burnt, or milky fluid is a problem.
• Rub fluid between your fingers. Grit or metal particles mean internal wear.
• Inspect hoses for cracks, bulges, dry rot, or chafing against the frame.

Machine running

• Extend the boom and arm fully and hold under load for two to three minutes. Cylinders that drift down have failing seals.
• Cycle every function and listen for whining, knocking, or sluggishness under load.
• Watch for new leaks once pressurized.

System 2: Undercarriage

The undercarriage is one of the most expensive things to replace and one of the easiest to overlook, because it sits low to the ground. Do not rush this check.

What to inspect

• Walk both tracks for cracked links, worn pads, and uneven wear.
• Check rollers and idlers for oil leaks, flat spots, and rust. Leaking rollers need replacement.
• Inspect sprocket teeth. Sharp or hooked teeth mean the tracks ran loose or stretched.
• Check track tension. Sag of more than an inch or two mid-span needs adjustment at minimum.
• Ask what terrain the machine worked in. Rock and concrete wear undercarriage two to three times faster than dirt.

How to estimate wear: Dealers use a track measuring tool for exact percentages. At 70 to 80 percent wear, factor it into your offer. At 90 percent or more, plan for full replacement.

System 3: Engine

Cold inspection

• Pull the oil dipstick. Milky or frothy oil means coolant is mixing in, usually a head gasket or cracked block.
• Check the coolant reservoir for oil contamination and the air filter for neglect.
• Inspect hoses, belts, and radiator fins for damage or debris.

Starting the machine

• Start it cold and idle 5 to 10 minutes. Light grey or white smoke on startup is normal and clears within a minute.
• Black smoke means incomplete combustion. Blue smoke means oil is burning, from worn rings or valve seals.
• Listen for knocking. Light valve tick is normal; deep knocking is not.

Once warm: Drive forward and backward on flat ground. Pulling to one side suggests a weak pump or drive motor. Shut down and check underneath for new fluid.

System 4: Slewing Ring

The slewing ring, or swing bearing, connects the cab structure to the undercarriage and takes enormous load over time. Replacement is expensive and labor-intensive.

How to check it

• Rotate the cab slowly in both directions. Grinding, popping, or hesitation means wear.
• Swing at full speed, then stop suddenly. A worn ring coasts noticeably further than a tight one.
• Sit in the cab while someone pushes and pulls the boom from outside. There should be no vertical rocking.
• With a dial indicator, measure play at four quarter-turn positions and average the readings.

System 5: Boom, Arm, and Bucket

Structural inspection

• Walk the boom and arm for cracks in the welds, especially at joints and cylinder mounts. Weld cracks are the most severe defect because they propagate under stress.
• Dents on top of the arm usually mean hard use. Grab the bucket and shake it: any play means worn pins or bushings.
• Blunt or unevenly worn bucket teeth signal heavy use.

Cylinder inspection: Exposed chrome should be clean and shiny, with no pitting or scoring. A light oil film is normal. Heavy weeping past the wiper seal means the seal needs replacement.

System 6: Cab

The cab tells you a lot about how the machine was treated overall.

What to check

• Operate every control: joysticks, pedals, switches, and the horn.
• Compare the hour meter to wear on pedals, seat, and joystick grips. Worn controls with low hours is a red flag.
• Check the seat, windows for cracks, and the headliner and floor for water staining.
• Test heat and air conditioning, and confirm warning lights and gauges work at startup.

When to Bring a Professional

If you are not comfortable evaluating these systems, or the machine is high-value enough to justify it, hire a third-party inspector. A professional inspection runs $500 to $1,000 and can surface what is easy to miss without tools: cycle timing against spec, proper track measurement, dial-indicator slewing ring play, and oil sample analysis. The cost is almost always less than the first surprise repair.

Red Flags That Should Stop the Deal

Some findings are reasons to walk away unless the price reflects the problem clearly:

Once you are satisfied with what you found, you know what to look for. PayDirt lists used excavator inventory, with financing options available through Equify Financial. And if you still need it, our used hydraulic excavator buying guide covers machine history, sourcing, and financing in more depth.