Caterpillartrack-type tractor

Caterpillar D6H XL

Maintenance schedule, common problems & OEM parts breakdown

The Caterpillar D6H XL is a medium crawler dozer featuring an elevated drive sprocket undercarriage and a Cat 3306 engine. Production spanned 1986 to 1996, succeeding the D6D and preceding the D6R. The XL configuration offered 175 hp and a weight range of 16 to 20 tons, varying by configuration and series.

The D6H XL introduced a modular powertrain for easier repair and a robust undercarriage design. It remains significant in the used market due to its durable Cat 3306 engine and widespread parts availability. The machine serves as a reliable workhorse for earthmoving, with many units still operating in forestry and construction sectors.

Below: full specifications, fluids & capacities, the factory service schedule, common service parts, verified fault codes, what owners discuss, attachment guidance, the complete assembly directory, and a serial-number reference. Complete parts lists with full OEM part numbers, exploded diagrams, quantities, and fitment data are available free in Heavy Parts AI.

Caterpillar D6H XL specifications

Engine

Model	Cat 3306 (6-cylinder diesel)
Gross Power	179 hp (133.5 kW)
Net Power	165 hp (123.0 kW)
Displacement	10.5 L (640.7 cu in)

Weights

Operating Weight

30,359 to 37,377 lb (13,770 to 16,954 kg); standard approx. 40,000 lb (18,144 kg) varies by configuration/series

Dimensions

Transport Length (w/ Blade)	5.0 m (16.4 ft)
Transport Width (Over Tracks)	2.35 m (7.7 ft)
Transport Height	0.08 m (10 ft 3 in)
Track Gauge	Not documented for this exact serial range — verify with your dealer
Track Shoe Width	457 mm (18 in)
Ground Clearance	Not documented for this exact serial range — verify with your dealer

Performance

Travel Speeds	Not documented for this exact serial range — verify with your dealer
Drawbar Pull	Not documented for this exact serial range — verify with your dealer
Gradeability	Not documented for this exact serial range — verify with your dealer
Ground Pressure	Not documented for this exact serial range — verify with your dealer

Blades

Blade Types Offered	Straight (S), Universal (U), S-U Combination, Power Angle Tilt (PAT)
Blade Capacities	Not documented for this exact serial range — verify with your dealer

Service Capacities

Fuel Capacity	321.7 L (85 gal)
Hydraulic System Capacity	72.7 L (19.2 gal)
Engine Oil Capacity	Not documented for this exact serial range — verify with your dealer
Cooling System Capacity	Not documented for this exact serial range — verify with your dealer

Values vary by configuration, region, and serial range — confirm against your machine before planning transport or lifts.

D6H XL fluids & capacities

System	Capacity	Recommended fluid
Engine Crankcase (with filter)	27.5 l (7.3 gal)	Cat DEO or DEO-ULC (API CF-4/SF or higher); viscosity varies by ambient temperature per SEBU6250-15
Cooling System	Not documented in source text	Caterpillar Extended Life Coolant (ELC); use Cat extender solution at 3000 hours to double coolant life
Fuel Tank	Not documented in source text	Not documented in source text
Transmission/Powertrain: Powershift Transmission	Not documented in source text	Cat TDTO (Transmission and Torque Converter Oil)
Transmission/Powertrain: Bevel Gear/Steering Compartments	Not documented in source text	Cat TDTO
Final Drives (each)	Not documented in source text	Cat TDTO
Hydraulic System/Tank	Not documented in source text	Cat HYDO Advanced; biodegradable hydraulic oils available; limit cross-contamination to less than 10% when switching oils
Pivot Shaft	Not documented in source text	Not documented in source text
Grease Specs	Not documented in source text	Not documented in source text

Capacities are refill values from factory literature — always fill to the dipstick/sight gauge, not the number.

Caterpillar D6H XL maintenance schedule

Service interval	Tasks
Every 10 h	Check engine oil level. Check hydraulic fluid level. Check coolant level. Drain water from fuel separator. Check air filter restriction indicator. Inspect for fluid leaks.
Every 250 h	Change engine oil and filter. Grease blade, push arms, ripper, and pivot points. Check final drive oil level. Check transmission oil level. Inspect undercarriage wear visually. Inspect belts and hoses.
Every 500 h	Replace fuel filter. Drain water from fuel separator. Replace hydraulic return filter. Test coolant SCA concentration. Check battery terminals and load. Inspect hydraulic hoses for abrasion.
Every 1,000 h	Change final drive oil. Clean or replace air filter primary element. Take hydraulic oil sample (S.O.S). Inspect turbocharger. Torque ROPS bolts. Measure undercarriage wear.
Every 2,000 h	Change hydraulic oil. Flush and replace coolant. Change transmission oil. Comprehensive structural inspection. Evaluate major components. Replace worn belts and hoses.

Servicing the D6H XL beyond the schedule

Predictive Maintenance & Fluid Analysis

Monitor S.O.S fluid samples at 1000-hour intervals to detect wear metals in the Cat 3306 engine and hydraulic system. Check coolant SCA concentration at 500 hours to prevent liner pitting. Analyze transmission oil for gear wear indicators. Use Cat DEO engine oil and HYDO Advanced hydraulic fluid to maintain system integrity. Early detection of coolant leaks or fuel dilution prevents catastrophic engine failure.

Corrective & Common Repairs

Address D6H XL overheating by cleaning radiator and oil cooler fins daily. Replace hydraulic return filters at 500 hours to protect the main pump. Inspect equalizer bars for stress cracks, as they are difficult to remove on this model. Check turbocharger condition at 1000 hours. Replace worn track shoes and side cutters to maintain undercarriage life and traction.

Overhaul & Rebuild Points

Plan engine overhaul around 10,000 to 15,000 hours based on S.O.S trends. Rebuild final drives when oil samples show high copper or iron content. Inspect transmission clutches and torque converter at 20,000 hours. Replace hydraulic pump seals if pressure drops occur. Evaluate undercarriage rollers and idlers for replacement when wear exceeds limits.

Seasonal & Environment Servicing

In dusty conditions, check air filters daily and replace at 500 hours. Use lower viscosity engine oil in cold climates for easier starting. Drain fuel water separator frequently in humid environments. Inspect hydraulic hoses for brittleness in extreme cold. Adjust track tension to prevent slippage in muddy conditions. Clean cooling system fins weekly in high-debris areas.

D6H XL fault codes & troubleshooting

Code	Meaning	Likely cause	What to do
CID 110 FMI 0	Engine Coolant Temperature — Above Normal	Low coolant level, failed thermostat, or blocked radiator core.	Check coolant level and inspect for leaks; do not operate until resolved.
CID 110 FMI 3	Engine Coolant Temperature Sensor — Voltage Above Normal	Open circuit or short to power in the sensor wiring.	Inspect harness for damage; replace sensor if confirmed faulty.
CID 190 FMI 8	Engine Speed — Abnormal Frequency	Speed sensor air gap error, sensor failure, or tone ring damage.	Check sensor gap and test speed sensor and tone ring.
CID 41 FMI 3	8-Volt DC Supply — Voltage Above Normal	Short to power on the 8V reference circuit.	Inspect sensors sharing the 8V supply and isolate the fault.
CID 41 FMI 4	8-Volt DC Supply — Voltage Below Normal	Short to ground on the 8V reference circuit.	Disconnect sensors one at a time to locate the short.
CID 164 FMI 2	Injection Actuation Pressure — Erratic Signal	Faulty sensor or intermittent wiring connection.	Check wiring connections and test sensor output.
CID 168 FMI 2	ECM Supply Voltage — Intermittent	Loose battery cables, poor ground, or failing alternator.	Check battery terminals, ground straps, and charging system.
CID 248 FMI 9	CAT Data Link — Abnormal Update Rate	CAN bus wiring damage or termination fault.	Check CAN wiring and measure termination resistance.

Codes and remedies are general guidance for this model family — always confirm with diagnostic tooling and your dealer before major repairs.

D6H XL attachments & work tools

Blades

The D6H XL supports S, SU, and U blade types; PAT (Power Angle Tilt) availability varies by configuration/series. Typical widths range from 3.05 m (10 ft) for the S-blade to 3.66 m (12 ft) for the U-blade, with capacities varying by configuration/series.

Rippers

Multi-shank and single-shank ripper options are available for this class, with weights varying by configuration/series. The XL undercarriage provides the necessary weight and stability for heavier variable pitch rippers often used in forestry applications.

Winches

A hydraulic winch class fits the D6H XL for towing or pulling tasks, particularly in forestry configurations. This option is typically paired with a lighter front blade to balance the machine when pushing brush and trees.

Drawbars/Counterweights

The rear of the machine can be outfitted with large steel slabs to add weight for heavy dozing applications. A drawbar and CCU (Cable control unit) are available for pulling towed scrapers, with later models using hydraulics in place of the CCU.

Cab/ROPS guarding

Forestry and waste configurations utilize four-post ROPS with an optional enclosed cab featuring air-conditioning. Guarding options include heavy-duty protection for the radiator and hydraulic lines to prevent damage from debris.

Hydraulic arrangement

The D6H XL Series II features an improved hydraulic system with a pump flow of 166.5 lpm (44 gpm) and a system capacity of 72.7 L (19.2 gal). Front and rear tool hydraulics are managed through this system, with fluid specifications including Cat DEO, TDTO, and HYDO Advanced.

All D6H XL assemblies by section

Every catalogued assembly group for the Caterpillar D6H XL. Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.

Basic Engine

268-3748 Kit-Engine Parts

11***18	Tube As-Fuel Ratio	1
11***28	Elbow; (90-Deg)	1
12***94	Bolt-Tamperproof; (28.58mm)	1
12***96	Bolt-Tamperproof; (95.25mm)	1

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284-7808 Kit-Hardware

0L***43	Bolt 63.5 mm (3/8" X 2 1/2" -Cover Assembly To Fender	1
0S***71	Screw,Cap,Hexagon; Tube Assembly To Turbocharger And Elbow Mounting	3
0S***91	Screw,Cap,Hexagon Bearing Retainer; Part Of Kit P/N 1w***82	1
0S***94	Bolt (1 In. Long 3/8 In. Dia.); Plate Assembly To Support Assembly	2

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Engine Arrangement

267-5717 Conversion Ar-Engine

0R***14	Rod As-Connecting	1
0R***24	Nozzle As-Fuel Injection	6
0R***88	Cylinder Pack Group	6
10***21	Turbocharger Group	1

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Fuel System

7c-8993 Fastener Gp-Fuel Inj Pump

0S***14	Bolt (.25" Diameter-.50" Long)	3
2S***83	Bolt (3.25" Long-Drilled Head)	1
4F***57	Screw,Cap,Hexagon H Shock Mount To Bracket	8
4N***61	Bolt 165.1 mm(6.5 In.) Long	4

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1w-8668 Torque Control Gp

1P***52	Insulator,Bushing Governor	1
1W***68	Torque Control Group	1
2P***85	Spacer (.635 mm Thk); (0.635-mm Thk)	1
2W***34	Bar-Load Stop; (4.0mm Thk)	1

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111-5162 Control Gp-Fuel Ratio

10***93	Washer	1
11***62	Control Group-Fuel Ratio (Basic)	1
11***58	Washer; (12.7x6.65x0.79-mm Thk)	1
2A***46	Bolt,Machine Governor Linkage Bracket	2

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2w-2410 Governor Gp

03***16	Bolt-Self Locking; (1/4unc X 3/4)	3
0S***16	Screw,Cap,Hexagon H Receptacle Mtg; Bolt Brackets To Firewall Assembly	6
13***07	Seal-Lip Type; (6.39mm)	1
15***28	Gasket-Governor	1

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4p-9827 Pump Gp-Fuel Injection

1W***87	Valve As-Check; (Fuel Injection Pump)	1
4P***27	Pump Group-Fuel Injection	1
4P***30	Plunger & Barrel Assem.	1
6I***27	Bonnet-Valve	1

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111-3769 Pump Gp-Fuel Injection

0S***15	Bolt 19 mm (.75 In.) Long Return Air Console To Enclosed Rops	4
11***69	Pump Group-Fuel Injection	1
11***70	Camshaft Group	1
11***71	Camshaft-Fuel Pump	1

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7c-8992 Seal Gp-Pump

03***79	Seal-O-Ring (Id=10.82mm)	1
14***77	Gasket	1
15***26	Gasket	1
15***27	Gasket-Fuel	1

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D6H XL serial number reference

The PIN plate is located on the right side of the machine frame, near the operator's station or on the rear counterweight. The prefix consists of the first three characters of the serial number, which identify the model series, generation, and configuration. Read the prefix from left to right at the start of the serial number string.

Prefix	Identifies	Notes
8KK	D6H XL Series II	Power shift transmission; powered by 3306 engine. Serial range 8KK00001-UP. Source: Parts manual listings and service repair manuals. Confirm with dealer for specific configuration details.
9LK	D6H XL	Serial range 9LK00001-UP. Source: Parts catalogue manual. Confirm with dealer for specific configuration details.
9KJ	D6H	Serial range 9KJ00001-UP. Source: Hydraulic pump application notes. Confirm with dealer for specific configuration details.
4GG	D6H	Serial range 4GG00001-UP. Source: Hydraulic pump application notes. Confirm with dealer for specific configuration details.
5HF	D6H	Serial range 5HF00001-UP. Source: Hydraulic pump application notes. Confirm with dealer for specific configuration details.
3YG	D6H	Serial range 3YG00001-UP. Source: Hydraulic pump application notes. Confirm with dealer for specific configuration details.
2TL	D6H XR	Serial range 2TL00001-UP. Source: Hydraulic pump application notes. Confirm with dealer for specific configuration details.
9KJ	D6H XL	Serial range 9KJ1-UP. Source: Undercarriage parts listing. Confirm with dealer for specific configuration details.
9LK	D6H XL	Serial range 9LK1-UP. Source: Undercarriage parts listing. Confirm with dealer for specific configuration details.

Frequently asked questions

What engine does the D6H XL use?

The D6H XL uses the Cat 3306 engine, producing 175 hp.

What is the operating weight of the D6H XL?

The operating weight ranges from 16 to 20 tons (18 to 23 short tons), varying by configuration and series.

What replaced the D6H XL?

The D6R replaced the D6H XL in 1996.

What D6H XL owners discuss

What are the primary powertrain and hydraulic differences between the D6H XL Series I and Series II?

The Series II variant features an improved hydraulic system that provides better performance than the Series I. The XL configuration includes seven track rollers compared to six on the standard tractor. The XL variant delivers 175 hp, whereas the standard tractor produces 165 hp. Series II tractors are noted for working much better due to these hydraulic improvements. Varies by configuration/series

How does the D6H XL perform in earthmoving compared to the D7E, and what are the limitations?

In good to reasonable materials, a D6H XL in good order will push more than an older D7E tractor. However, the D7E has extra weight that makes it superior in hard and difficult materials. The standard D6H struggles to match the D7E, but the XL variant is competitive in favorable conditions. The D6H XL is considered a great trimming dozer; it is well-balanced and nippy on its feet. Varies by configuration/series

What are the typical undercarriage wear patterns and structural failure points for the D6H XL?

Track frames are prone to cracking and subsequent welding, with a risk of recracking. Equalizer bars are difficult to remove for repair and may develop play. Idler wheels can become thin and require welding. Track pads may wear down to approximately 20 percent of their original thickness. The XL undercarriage is preferred over the standard configuration for durability. Varies by configuration/series

What engine specifications and quirks are associated with the D6H XL?

The D6H XL is powered by a 3306 Caterpillar engine displacing 640.7 cubic inches. It produces 165 hp in the standard configuration and 175 hp in the XL variant. Operators have reported issues with serious black smoke and loss of power, which may indicate injector pump, injector, or timing problems. The engine is described as reliable when maintained, but fuel consumption and power delivery depend heavily on the specific series and configuration. Varies by configuration/series

What are the common cooling system and radiator issues for the D6H XL?

The radiator features a 12-core V-shaped design that includes a hydraulic cooler and dual condensers. The radiator cores are notably thin, which leads to clogging and inadequate cooling performance. Clogging restricts airflow and causes the engine to overheat. Cooling system construction is a primary source of heat management issues in this machine type. Varies by configuration/series

What electrical or sensor issues are commonly reported by operators?

Operators report transmission overheating and slow cooling, often accompanied by a plugged transmission filter alarm. The forward-to-reverse handle can become stiff to turn, potentially requiring lubrication or hydraulic adjustment. While specific sensor failure rates are not quantified, the transmission control system is a known point of concern requiring regular monitoring of fluid condition and filter status. Varies by configuration/series

What should be checked when buying a used D6H XL?

Inspect track frames for cracks and previous welds, as recracking is common. Check equalizer bars for excessive play (up to 1 inch reported). Verify the condition of idler wheels, which are often thin and welded. Assess undercarriage life, noting that pads may be worn to 20 percent. Check transmission fluid for condition and the filter for debris. Verify the serial number prefix to determine the exact series and configuration, as specs vary significantly between Series I and II. Have your dealer verify the structural integrity of the track frames and the condition of the differential steer components. Varies by configuration/series

Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.

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