The CAT D6 sits in the mid-size dozer class, and it's arguably the most versatile crawler on a general contractor's lot — big enough for real production in site development, land clearing and road work, small enough to transport without a specialist permit every time. That popularity cuts both ways on the used market: good machines sell quickly, and hard-used ones get dressed up and sold quickly too.
Know which D6 you're looking at
"D6" covers several generations, and they are not interchangeable in price or capability. You'll see machines carrying suffixes from earlier eras — R, N, T and similar — as well as the current-generation D6 and the high-efficiency D6 XE. Broadly:
- Older lettered generations are mechanically simpler, cheaper to buy, and often easier to service independently. If you don't need integrated grade control, they can be excellent value.
- Later and current-generation machines bring updated powertrains, better cabs, improved emissions systems and factory grade-control integration. They cost more up front and can require dealer-level diagnostics.
- XE machines use a high-efficiency drivetrain aimed at reducing fuel burn, which matters most on high-hour production work.
Also check whether the machine is a standard, LGP (low ground pressure) or XL configuration. LGP machines run wider tracks and spread weight over more area — essential on soft ground, but they trade some stability and durability on rock. Buying the wrong configuration is a costly mistake that specs alone won't warn you about.
Confirm the exact generation and build year from the machine's serial number rather than trusting the listing text — our serial number guide shows you how.
The undercarriage is the whole ballgame
If you check one thing on a used dozer, check this. Undercarriage is the single largest wear expense on a crawler, and a full rebuild is a major cost that can rival a meaningful share of the machine's purchase price. A cheap dozer with a worn-out undercarriage is not cheap.
What to look at:
- Track shoes and grousers — measure remaining grouser height; heavily rounded grousers mean lost traction and a looming replacement.
- Sprockets — sharpened, hooked teeth are a clear wear indicator.
- Idlers and rollers — look for flat spots, wobble and oil weeping from seals. A leaking roller is already failing.
- Track tension and pin/bushing wear — excessive slack and turned or re-turned bushings tell you how much life is left.
- Ask for a formal undercarriage measurement. Dealers and service shops do this routinely and it converts guesswork into a percentage-remaining figure. Any serious seller should be willing to provide or allow one.
Powertrain and hydraulics
- Cold start it. Insist on it. A cold start exposes hard starting and smoke that a pre-warmed machine hides. Blue smoke suggests oil burning; heavy black smoke points to fuel or air issues.
- Check transmission and final drive behavior. Test forward and reverse in every range. Listen for whine and feel for harsh or delayed engagement. Inspect final drives for leaks — they're expensive.
- Test steering under load. Push a pile and steer both ways. Uneven pulling or slow response can indicate steering clutch or brake wear.
- Pull the fluids. Milky oil means coolant intrusion. Burnt or gritty hydraulic fluid means neglect. Compare against the service records.
- Cycle every hydraulic function. Raise, lower, tilt and angle the blade; run the ripper if fitted. Watch for drift, hesitation and weeping cylinders.
Blade, ripper and grade control
The attachment package changes the value materially, so price it separately:
- Blade type. Straight (S), semi-universal (SU) and universal (U) blades suit different work — SU is the common all-rounder on a D6-class machine. Check the moldboard for cracks, heavy weld repair and straightness, and look at cutting edge and end bit wear.
- Ripper. A multi-shank or single-shank ripper adds real value if you need it. Inspect the shanks, pockets and mounting for cracks.
- Grade control. Factory-integrated grade control is worth a significant premium if you'll use it — and worth verifying that it actually works and that any subscription or licensing is transferable. Confirm this in writing before purchase, not after.
Hours, records and the honest math
Judge hours against the roughly 1,000–1,200 hours per year benchmark, but weight documentation just as heavily — a high-hour D6 with complete records and a recently rebuilt undercarriage is frequently the better buy over a low-hour machine with no history. Our guide to operating hours covers how buyers price this.
Before you negotiate, total up every deferred cost you found — undercarriage percentage remaining, cutting edges, leaking cylinders, pending services — and bring that number to the table. That's your leverage, and it's the difference between a good buy and an expensive lesson.
Next steps
Run the full 10-point inspection checklist on any candidate, get a pricing baseline from the free Equipment Value Estimator, then browse dozers and other heavy equipment on EquipMarket. Buyer financing is available for qualified purchasers, so a strong machine at a fair price doesn't have to tie up your cash.
