Caterpillarexcavator

Caterpillar M325B

Maintenance schedule, common problems & OEM parts breakdown

The Caterpillar M325B MH is a wheeled material handler, not a bucket-digging crawler excavator. It runs on a fabricated chassis with four-wheel hydrostatic drive and two-wheel steer — a trunnion-mounted front drive/steer axle and a solid-mount rear drive axle — built on the 325B excavator platform for scrap, millyard, and waterfront handling work. Power comes from a Cat 3116 TA turbocharged inline-six diesel, 6.6 L displacement, rated 132 kW (177 hp) gross and 125 kW (168 hp) net, using mechanical sleeve-metering fuel injection with an electronically controlled governor rather than a full engine ECM. Operating weight runs around 37,200 kg (82,040 lb) and varies with the front attachment and counterweight fitted. Factory front-end options include grapples, an orange-peel bucket, an electromagnet with its own hydraulically driven generator, a heel-boom, and a butt-n-top configuration.

Caterpillar carried the wheeled material-handler concept forward through the M325C MH and later M325D MH, M325D L MH, and M325D LM generations, each adding updated hydraulics, cab, and, on later D-series machines, electronic engine controls the M325B never had. The M325B MH's mechanically injected 3116 and simple hydrostatic driveline make it a straightforward, field-serviceable machine with no engine ECM to fault-code, which keeps it attractive to scrap and demolition yards that run older iron hard and want fewer electronics to chase. Documented serial-number ranges for this exact model are thin, so build year and factory configuration should be confirmed with a dealer. In the parts market it survives mainly on 325B-platform commonality — engine, hydraulic pump, and axle components — plus salvage sourced from the wider MH family.

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 M325B specifications

Engine

Engine model	Cat 3116 TA — turbocharged and aftercooled, inline six-cylinder diesel
Gross power	132 kW (177 hp) at 2000 rpm
Net flywheel power	125 kW (168 hp) at 2000 rpm, per ISO 9249, SAE J1349 and EEC 80/1269
Displacement	6.6 L (403 in³)
Bore x stroke	105 mm x 127 mm (4.13 in x 5.00 in)
Cylinders	6, inline, turbocharged and aftercooled, two-piece pistons
Emissions	Rated to meet the worldwide emissions standards in effect at the time of manufacture for this engine family; no specific numbered emissions tier is published in factory literature for this model year

Weights

Operating weight (standard, 13.4 m two-piece front, 20 kW generator)	37 200 kg (82,040 lb)
Upper structure weight	9470 kg (20,880 lb)
Counterweight	7700 kg (16,980 lb) — roughly 50% heavier than a standard digging-configuration counterweight
Lower/carrier weight, including carbody	14 365 kg (31,675 lb)
Two-piece front weight, with cylinders	5665 kg (12,500 lb)
Ground pressure	Not published — this is a wheeled (tire-mounted) carrier, not a track undercarriage, so Cat does not issue a ground-pressure rating for it
Transport weight	Not listed as a separate figure; factory literature gives only the operating weight and component breakdown above

Dimensions

Operating height to top of cab (1.9 m cab riser)	5892 mm (19'4")
Cab height, optional 0.76 m low riser with Falling Object Guard	4.78 m (15'8")
Shipping height, cab tipped forward	3759 mm (12'4")
Operating width, outside of tires	3226 mm (10'7")
Width, outriggers up	3505 mm (11'6")
Width, outriggers down	5280 mm (17'3")
Shipping length, with 13.4 m front	10 508 mm (34'6")
Length of carrier	6147 mm (20'2")
Ground clearance, carrier	356 mm (1'2")
Ground clearance under outriggers	508 mm (1'8")
Wheelbase	3200 mm (10'6")
Swing center to tire centerline	1524 mm (5'0")
Tail swing radius	Not published for this configuration
Tires (wheeled carrier — no track shoes)	20.5-R25 XMineD2 or 23.5-R25 XHA L3 pneumatic tires, or 16-25 solid tires

Performance

Maximum reach, 15.5 m two-piece front	15.5 m (50'10")
Maximum reach, 13.4 m two-piece front	13.4 m (43'11")
Maximum reach below ground (dig-depth equivalent, 15.5 m front)	6.5 m (21.2 ft)
Maximum vertical pin height, 15.5 m front	17.0 m (55'7")
Maximum vertical pin height, 13.4 m front	15.3 m (50'4")
Maximum dump height / cutting height	Not applicable — machine is fitted with grapples, an orange-peel bucket, or an electromagnet rather than a digging bucket with a cutting edge
Swing speed	10 rpm
Travel speed, high range	19.8 km/h (12.3 mph)
Travel speed, low range	5.2 km/h (3.2 mph)
Gradeability	43%
Maximum drawbar pull	14 830 kg (32,700 lb)

Forces

Bucket/grapple digging (breakout) force	Not published — factory literature does not rate a bucket digging force for this material-handling configuration
Stick (arm) digging force	Not published for the same reason; this configuration is not sold with a digging bucket
Swing torque	76 kN·m (56,080 lb·ft)

Service capacities (summary)

Fuel tank	420 L (111 gal)
Hydraulic system, including tank	310 L (82 gal), of which the hydraulic tank alone holds 175 L (46 gal)
Engine oil	20 L (5.3 gal)
Cooling system	31.5 L (8.3 gal)

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

M325B fluids & capacities

System	Capacity	Recommended fluid
Engine crankcase (with filter)	20 L (5.3 US gal)	Cat DEO diesel engine oil. SAE 15W-40 for normal to warm ambient service; switch to SAE 10W-30 in cold climates for easier cold starting. A multigrade blend covering the local seasonal range is acceptable.
Cooling system	31.5 L (8.3 US gal)	Factory-fill coolant is a 50% concentration antifreeze mix rated to -34 C (-30 F). Use Cat conventional coolant (DEAC) or Cat Extended Life Coolant (ELC) per the machine's coolant specification; the two chemistries are not to be mixed in the same system.
Fuel tank	420 L (111 US gal)	No. 2-D diesel fuel for normal ambient operation; switch to No. 1-D diesel in cold ambient for better cold-flow and starting performance.
Hydraulic system (total, incl. tank) / Hydraulic tank	Total system 310 L (82 US gal); hydraulic tank 175 L (46 US gal)	Cat HYDO hydraulic oil. Use SAE 10W in cold ambient conditions and SAE 30 in normal-to-hot ambient; select grade seasonally for the operating climate.
Final drive (each)	8 L (2.1 US gal) per side	Cat TDTO transmission/drive train oil. SAE 30 for normal ambient temperatures; SAE 10W for cold-weather startup conditions.
Swing drive	10 L (2.6 US gal)	Cat TDTO transmission/drive train oil, same grade selection as the final drives - SAE 30 in normal ambient, SAE 10W in cold weather.
Pilot / other hydraulic circuits	No separate reservoir; pilot and auxiliary (rotate/generator) circuits draw off the main hydraulic tank	Same Cat HYDO fluid used in the main hydraulic system; no distinct fluid or fill point.
Grease (spec only)	Not a bulk-fill reservoir; applied at individual pin, bushing, and linkage grease points	Cat Multipurpose Grease (NLGI 2, lithium-complex EP) for boom, stick, linkage, and outrigger pin points. Use an arctic-grade multipurpose grease where ambient temperatures run below roughly -20 C.

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

Caterpillar M325B maintenance schedule

Service interval	Tasks
Every 10 h	Check engine oil, coolant, and hydraulic tank levels before starting the shift. Walk down both axles, the swing frame, and the front linkage looking for hydraulic leaks, loose fasteners, or damaged hose routing. Grease boom, stick, and front-tool pivot pins (grapple, orange-peel, magnet, or heel-boom linkage) on the weekly cycle. Drain water and sediment from the fuel/water separator. Check tire condition, wheel-nut torque, and the front oscillating-axle lock pin. On magnet-equipped fronts, confirm generator output and cable condition before starting magnet duty.
Every 250 h	Change engine oil and filter on the 3116 TA; bleed the fuel system fully before restart since the mechanical filter housing traps air easily. Clean the turbocharger compressor housing and aftercooler core of yard dust and fine metal debris. Check front and rear axle oil level and inspect the trunnion-mounted front axle oscillation bushings. Re-torque swing bearing and counterweight mounting bolts. Grease all upper-frame and front-linkage pivot pins, including the rotate-circuit bearing on grapple or orange-peel fronts. Pull an oil sample from the engine and the hydrostatic drive circuit for analysis.
Every 500 h	Replace the primary and secondary fuel filters and bleed the fuel system completely to purge trapped air. Change front and rear axle (differential/final-drive) oil. Inspect the hydrostatic travel motors and wheel-hub disc brakes for leakage and lining wear. Check the hydraulic tank breather and return-line filter; replace if restricted. Inspect quick-coupler and tool-interface wear plates, and check the rotate-circuit gear pump for cycle-speed loss. On magnet-equipped fronts, check generator brush wear and output voltage.
Every 1,000 h	Change the hydraulic system return filter element and check the tank for water or sediment. Inspect valve lash and injector setting on the 3116 TA; adjust if outside factory spec. Change swing drive gearbox oil. Inspect upper-frame welds near the swing bearing deck and boom-foot pin bosses for fatigue cracking — the heavier counterweight and longer fronts raise loading here. Check turbocharger shaft end play. Inspect wiring and connectors on the magnet generator system for chafing or corrosion.
Every 2,000 h	Change hydraulic system oil (extend to 3000 hours only if running Cat HYDO Advanced). Adjust valve lash and verify injection timing on the 3116 TA. Inspect and shim the swing bearing; re-torque mounting bolts to the factory sequence. Inspect front and rear axle bearings and seals for overhaul-level wear. Pressure-test the travel, swing, and rotate/grapple relief valves against factory spec.
Every 4,000 h	Flush and refill the cooling system with fresh coolant and pressure-test the radiator and aftercooler circuit. Inspect the hydrostatic drive pump and travel motors for internal wear; rebuild as needed. Check swing bearing bolt stretch and gear backlash; replace the bearing if beyond the wear limit. Inspect boom, stick, and front-tool linkage pins and bushings for oversize wear from repeated grapple, magnet, or orange-peel cycling.
Every 6,000 h	Perform a 3116 top-end overhaul covering injectors, the mechanical transfer pump, and the turbocharger. Rebuild or exchange the front and rear axle differentials and final drives. Run a structural crack inspection on the upper frame, counterweight mounts, and swing bearing deck. Rebuild the magnet generator and its drive circuit before returning the machine to heavy magnet duty.

Servicing the M325B beyond the schedule

Predictive Maintenance & Fluid Analysis

Run oil sampling on the 3116 TA's mechanical injection system — its upside-down fuel filter traps air easily, so watch for fuel dilution and moisture in engine oil before it reaches injectors and the transfer pump. Sample front and rear axle (differential/final-drive) oil and the hydrostatic drive circuit for wear metal that signals travel-motor or axle-bearing wear. Check swing bearing grease purge for water or fines. On magnet-equipped fronts, log generator output voltage and cable resistance trends to catch winding degradation before a dropped load.

Corrective & Common Repairs

Expect fuel-system air ingestion on the 3116 TA after filter changes — bleed thoroughly or injectors run rough and wear the cup bore. Watch the mechanical transfer pump's internal spring and check valves for pressure loss. On the chassis, trunnion front-axle oscillation bushings and wheel-hub disc brakes wear from constant yard maneuvering; hydrostatic travel motors leak at the shaft seal. On the upper end, the rotate-circuit gear pump loses output and slows grapple or orange-peel cycle speed, and quick-coupler wear plates need shimming or replacement.

Overhaul & Rebuild Points

The M325B MH's heavier counterweight and longer material-handling fronts load the swing bearing, gear, and upper-frame structure harder than a standard 325B digging machine. Inspect welds near the swing bearing deck and boom-foot pin bosses for fatigue cracking, and plan on swing bearing and gear replacement sooner than on a standard excavator. Rebuild points include the hydrostatic drive pump and travel motors, front and rear axle differentials and final drives, and a 3116 top-end overhaul covering injectors, the transfer pump, and the turbocharger at high hours.

Seasonal & Environment Servicing

Waterfront and scrap-yard duty exposes the chassis, axles, and hydraulic rams to salt, moisture, and abrasive fines — flush and re-grease exposed pivot pins more often and check ram-rod chrome for pitting. Clean the turbocharger and aftercooler of millyard dust that chokes airflow and raises exhaust temperatures. Before cold weather, switch to the correct viscosity engine and hydrostatic drive oil grades and top off coolant with fresh Cat coolant. Inspect magnet generator wiring and connectors for weatherproofing where the unit sits exposed on the front linkage.

M325B fault codes & troubleshooting

Code	Meaning	Likely cause	What to do
1302	Engine oil pressure below the normal operating range	Low oil level, worn oil pump, clogged oil filter, or a failed oil pressure sensor/switch	Shut the engine down immediately, check oil level and filter condition, and verify sensor wiring before restart
1303	Engine coolant temperature above the normal operating range	Low coolant level, a blocked radiator core, a failed thermostat, or a slipping/failed fan drive	Idle down and shut off the engine safely, check coolant level and radiator core for debris, and inspect the fan drive and thermostat
1304	Hydraulic oil temperature above the normal operating range	Low hydraulic oil level, a clogged oil cooler core, a faulty cooling fan, or a relief valve stuck open generating excess heat	Reduce load and idle the machine to cool down, check hydraulic oil level and cooler for blockage, and inspect the fan drive
1305	Return or inlet filter element restricted	Filter element loaded with contamination, or cold oil viscosity tripping the bypass indicator	Inspect and replace the flagged filter element and confirm the oil grade matches ambient temperature
2201	Charging system voltage outside the normal range	A failing alternator, loose or corroded battery connections, or a bad voltage regulator	Check alternator output and battery terminal condition, then test the charging circuit wiring
2301	Governor (throttle) actuator feedback sensor circuit shorted to ground	Chafed harness wiring near the governor motor, a corroded connector, or a failed feedback potentiometer	Inspect the governor actuator connector and harness for a short to frame ground, then test the feedback sensor resistance
2302	Governor actuator feedback signal unstable or deviating from the commanded position	A worn or dirty feedback potentiometer, loose linkage at the governor motor, or an intermittent connector	Clean and check the governor actuator linkage and connector, and verify the feedback signal with a service tool before replacing the actuator
4102	Controller/monitor supply voltage above normal	Charging system overvoltage, a faulty voltage regulator, or jump-start damage	Check charging voltage at the battery, inspect the regulator, and correct the overvoltage condition before further operation
4202	Engine speed signal abnormal or erratic	A faulty engine speed (magnetic pickup) sensor, a damaged timing ring, or an incorrect sensor air gap	Check the speed sensor air gap and wiring, and inspect for debris on the sensor tip

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

M325B attachments & work tools

Buckets

Factory literature covers this chassis only as the M325B MH Wheeled Material Handler, built for scrap, millyard, and waterfront handling rather than digging. No digging bucket capacity, width, or pin diameter is published for this nameplate — the closest factory-listed bucket-type tool is an orange-peel grapple, not a GD/HD digging bucket. If a digging front is built up outside the factory scrap-handling package, bucket fit is not covered by any published chart and must be confirmed with your dealer.

Hydraulic hammers

No hammer is factory-matched to the M325B. Cat's wheeled-excavator hammer-matching literature only extends up to M324 and does not list M325 at any letter suffix, and the M325B's hydraulic system is built around grapple open/close and rotate duty cycles rather than the sustained flow a breaker needs. Fitting a hammer to this carrier would require a dealer-engineered high-flow circuit sized to its actual operating weight rather than a catalog pairing.

Quick couplers

The M325B falls outside Cat's general-purpose pin-grabber and CW coupler matching guides for wheeled excavators, which stop at M322. Coupler fitment on this chassis is treated as a special/non-current-machine case in Cat's own literature, so pin spacing and linkage class should be confirmed directly with your dealer rather than assumed from a listed wheeled-excavator size class.

Thumbs / grapples

The documented factory work tool for the M325B MH is the Cat four-tine orange-peel grapple, offered in roughly 0.76 m³ and 1.15 m³ (1 and 1.5 yd³) sizes. Grapple open/close draws off the main high-pressure implement circuit, while grapple rotation runs on its own medium-pressure auxiliary circuit with a separate, fully adjustable control valve so flow can be tuned to different grapple-maker requirements. No excavator-style thumb attachment is documented for this model.

Rippers

No ripper attachment is documented for the M325B. Its factory front lineup is limited to two-piece MH linkages plus a heel-boom log-handling front and a butt-n-top log-sorting front for millyard work, none of which are set up to carry a ripper tooth.

Hydraulic-kit notes

The M325B MH runs two main pumps rated around 208 L/min (55 gal/min) each, with maximum implement pressure near 34 300 kPa (4,980 psi); that same high-pressure circuit feeds grapple open/close. A separate medium-pressure auxiliary circuit, about 30 L/min (8 gal/min) at roughly 17 200 kPa (2,500 psi), powers grapple rotation through its own adjustable control valve, and a third auxiliary pump — about 174 L/min (46 gal/min) at the same 17 200 kPa (2,500 psi) — drives a hydraulically powered 20 kW generator for electromagnet lifting work. Any added work-tool circuit should be sized against these existing pump ratings rather than a generic hammer or coupler flow chart.

All M325B assemblies by section

Every catalogued assembly group for the Caterpillar M325B. Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.

Frame And Body

2040650 Riser Arrangement

20***70	Riser Group	1
20***50	Riser Arrangement	1
20***51	Lines Group; Lines Gp - Pilot	1
20***52	Lines Group-Control; Lines Gp - Control	1

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Hydraulic System

2039734 Accumulator Gp

20***34

Accumulator Group

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2109149 Hose As

21***49

Hose As

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2040651 Lines Gp - Pilot

20***51

Lines Group; Lines Gp - Pilot

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2039733 Lines Group

20***33

Lines Group

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2040652 Lines Gp-Control

20***33	Lines Group	1
20***34	Accumulator Group	1
20***52	Lines Group-Control; Lines Gp - Control	1
8T***21	Washer-Hard; (11x21x2.5-mm Thk)(M10x1.50x30mm)	8

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Operator Station

2008870 Riser Gp

20***70

Riser Group

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Frequently asked questions

What engine does the Caterpillar M325B MH use?

A Cat 3116 TA turbocharged inline-six diesel, 6.6 L displacement, rated 132 kW (177 hp) gross and 125 kW (168 hp) net. Fuel delivery is mechanical sleeve-metering injection with an electronically controlled governor — this model has no full engine ECM.

What is the operating weight of the Caterpillar M325B MH?

Around 37,200 kg (82,040 lb) in factory configuration. Actual weight varies with the front attachment fitted — grapple, orange-peel bucket, magnet, heel-boom, or butt-n-top — and the counterweight used.

What replaced the Caterpillar M325B MH?

Caterpillar carried the wheeled material-handler concept forward with the M325C MH, then the M325D MH, M325D L MH, and M325D LM generations, each updating the hydraulics, cab, and, on later D-series machines, the engine controls.

What M325B owners discuss

What should I expect from the M325B MH's drive system as the machine racks up hours?

The M325B MH carrier runs four-wheel hydrostatic drive with two-wheel steer, so there is no torque converter or powershift gearbox to service. As the charge pump and drive motors wear, the earliest symptom is a soft loss of travel speed, most noticeable climbing a yard ramp or a ballast pile that used to be no trouble. Low charge pressure lets the low side of the loop cavitate, and once pitting starts on the piston faces it progresses fast, so a machine that traveled fine a month ago can drop off quickly. Check charge pressure and drive motor case-drain flow at scheduled service instead of waiting for an operator complaint. Any pressure reading below spec, have your dealer verify before running the drive under load again.

The engine never throws a fault code. Is something wrong with the sensors?

Not necessarily. The M325B MH is rated with the 3116 TA at 125 kW (168 hp) net flywheel power, and most 3116 engines of this era run mechanical unit injection with a mechanical governor and no engine ECM. There is simply no electronic fault log to read, which is normal for the vintage rather than a sign of failed sensors or neglected maintenance. Judge engine condition with oil analysis, a blowby check, and exhaust color instead of expecting a stored code to point you at a problem.

What engine problems come up most often on the 3116 in these machines?

Three issues recur across 3116-powered equipment generally, not just this application. Injector tip O-rings harden with age and start leaking combustion gas past the injector, showing up as a rough idle or gradual power loss. Aftercooler cores crack and let coolant migrate into the intake charge, which shows up as sweet-smelling exhaust or steady coolant loss with no visible external leak. Oil cooler O-rings seep over time and can look like a much bigger leak than they are. None of these are wear items unique to the M325B MH, they are known 3116 traits. A suspected aftercooler crack needs prompt attention since coolant pulled into a cylinder on startup can hydrolock it, have your dealer verify before the machine goes back to work.

What electrical problems are common on older M325B MH units?

Since the mechanical 3116 has no ECM, most electrical complaints trace back to the carrier's own wiring and starting aids rather than an engine sensor network. The intake air heater relay and its wiring are the most reported cold-start culprit, corrosion or a tired relay leaves the heater cycling erratically and shows up as hard starting in cool weather. Beyond that, expect the usual high-hour gremlins on a machine this age: corroded ground straps, worn battery cable terminals, and gauge or warning-light flicker traced to a loose bulkhead connector. Check the heater relay and grounds first before chasing anything more involved.

What wears fastest on the M325B MH's undercarriage compared to a tracked excavator?

There is no track chain or roller frame to wear on this carrier, tires and the front axle absorb the load a crawler would otherwise spread across a longer footprint. Tire life runs a few thousand hours on a wheeled carrier this size before replacement, less if the yard surface is rough or the machine works close to curbs and dock edges where sidewalls take repeated hits. The front axle oscillates and can be locked in place with a hydraulic stabilizer for load stability during grapple work, and that lock and its seals are worth a visual check since a sticking or leaking lock changes how the machine sits under a swung load. Rough yard surfaces put short, heavy load spikes on individual tires as the axle rocks, so look for wear concentrated on one corner instead of even wear all around.

What should I watch on the grapple and rotate hydraulics?

The rotate circuit runs its own gear pump separate from the main implement circuits, so slow, jerky, or one-direction-only rotation usually points to that pump or its control valve rather than the main hydraulic pump. At the grapple head, inspect the rotator swivel joint and hose routing for twisting or chafing, hoses that are not properly shielded through a full jaw open and close cycle tend to wear through at the same spot repeatedly. A grapple that rotates freely empty but binds once loaded usually means worn rotator bearings or a relief valve that has drifted low. Have your dealer verify relief pressure before adjusting it in the field, setting it wrong can overload the rotator seals.

What should I check before buying a used M325B MH?

First confirm it is actually the wheeled M325B MH and not the tracked 325B MH, listings and dealers sometimes shorten both to '325B MH' even though they are different carriers with different drivetrains. Match the data plate and engine serial against the machine in front of you, not the ad title. On the walkthrough: cycle the hydrostatic drive forward and reverse and up a grade to feel for soft travel or hunting, exercise the front axle stabilizer lock through a full cycle, run the grapple rotate circuit both directions under load, and if the machine has a cab riser, run it up and down checking for binding. Ask for oil analysis history rather than an engine diagnostic printout, since the mechanical 3116 keeps no electronic log. Walk the tires for wear concentrated on one corner, and check the counterweight mounting and welds for cracking, this configuration carries a notably heavier counterweight than a standard excavator of the same size to handle reach and swinging loads. Any hydraulic drift or drive irregularity found during the walkthrough, have your dealer verify before you finalize the purchase.

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

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