Caterpillar 938G
Caterpillarwheel-type loaderwheel loader

Caterpillar 938G

Maintenance schedule, common problems & OEM parts breakdown

The Caterpillar 938G is a mid-size, four-wheel-drive articulated wheel loader in Cat's 938 lineup, built from 1998 to 2003 and carried forward as the 938G Series II from 2003 to 2008. The original 938G runs a turbocharged, aftercooled Cat 3126 DITA diesel with mechanical unit injection, rated about 118-119 kW (158-160 hp) at the flywheel. The Series II switched to the electronically controlled Cat 3126B HEUI diesel with ATAAC, rated near 119 kW (160 hp) standard and up to 134 kW (180 hp) with power management engaged. Operating weight runs roughly 13.1 to 14.0 t (28,900-30,800 lb) depending on series and configuration. Cat offered the platform as a standard wheel loader and as the IT38G integrated toolcarrier, sharing the same engine and driveline but built around a quick-coupler front end for multi-tool work. In the model line, the 938G followed the 938F and was eventually succeeded by the 938H.

The main change inside the G generation came with the 2003 Series II update: the mechanical 3126 gave way to the electronically controlled 3126B HEUI engine, ATAAC turbocharging was added, and the third-function coupler valve moved to an electro-hydraulic switch in the cab instead of a mechanical lever. The frame, axles, and electronic-planetary powershift transmission carried over largely unchanged across both builds. In the used and parts market, the 938G still turns up in aggregate, waste, and general yard fleets because the platform is mechanically straightforward, and parts for the engine, transmission, axles, and loader linkage remain widely available through Cat and aftermarket rebuild channels. Running costs sit below the 938H, 938K, and 938M models that followed, which keeps the 938G in demand as a lower-cost entry point into Cat wheel loader capability. The mechanical-versus-electronic engine split between the 938G and 938G Series II is the detail that matters most for diagnostics and parts sourcing when buying used.

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 938G specifications

Engine

Engine model (938G, 1998-2003)Cat 3126 diesel, six-cylinder, turbocharged, water-jacket aftercooled (DITA)
Rated (gross) flywheel power (938G) @ 2200 rpm108 kW (145 hp)
Peak flywheel power (938G) @ 1900 rpm115 kW (158 hp), from torque-rise over the working range
Net power (938G, ISO 9249 / SAE J1349 / EEC 80/1269)108 kW (145 hp); 151 PS per DIN 70020
Displacement7.2 L (439 cu in), unchanged across 938G and 938G Series II
Bore x stroke110 mm x 127 mm (4.3 in x 5.0 in)
Peak net torque @ 1400 rpm (938G)765 Nm (564 lb-ft), total torque rise 54%
Emissions (938G)Meets EU Oct 1998, US EPA Jan 1997, and Japan MOC April 1997 requirements (Tier 1-equivalent era)
Engine model (938G Series II, 2003-2008)Cat 3126B with HEUI fuel injection, ADEM III electronic control, and air-to-air aftercooling (ATAAC)
Flywheel power (938G Series II) @ rated speed119 kW (160 hp)
Maximum flywheel power (938G Series II)134 kW (180 hp); some equipment databases round this to 179.7 hp gross
Emissions (938G Series II)Meets EPA Tier 2 emission requirements
Altitude derating (938G)No derating required up to 2300 m (7500 ft) altitude

Weights

Operating weight, 938G standard machine13,030 kg (28,731 lb) with 2.1-2.8 m3 (2.75-3.65 yd3) general-purpose bucket and standard 20.5-25 tires, per factory base spec
Operating weight, 938G as commonly configuredvaries by bucket/tire/options, roughly 13,030-13,181 kg (28,731-29,059 lb) across published configurations
Operating weight, 938G Series IIvaries by configuration, roughly 13,452-13,979 kg (29,657-30,819 lb) depending on tire and bucket selection
Operating weight, 938G/IT38G waste-handler arrangement14,325 kg (31,515 lb) standard-lift, 14,717 kg (32,377 lb) high-lift; special-application configuration with 4.2 m3 (5.5 yd3) waste bucket, not the general loader configuration
Static tipping load, full turn (938G standard config)approximately 10,390-10,517 kg (22,859-23,186 lb); varies with bucket and tire choice
Static tipping load straight, waste-handler config12,153 kg (26,736 lb) standard-lift, 9,908 kg (21,798 lb) high-lift, with 4.2 m3 waste bucket
Shipping weightnot separately published in factory literature; operating weight above reflects the machine with standard bucket, full fluids, and operator

Dimensions

Overall length with bucket on ground (938G)approximately 7.33-7.35 m (24.0-24.1 ft), depending on bucket fitted
Overall length with bucket on ground (938G Series II)approximately 7.19-7.22 m (23.6-23.7 ft)
Width over tires2.594-2.607 m (102.1-102.6 in), depending on tire selection; tread width is fixed at 2020 mm (80 in) for all tire options
Height to top of cabapproximately 3.31-3.32 m (10.86-10.9 ft)
Ground clearance400-427 mm (15.7-16.8 in), depending on tire selection
Wheelbaseapproximately 3.05 m (10.0 ft)
Minimum turning radius, over tire5.48 m (18 ft)
Steering angle, each direction40 degrees
Maximum single-wheel rise/fall (oscillating rear axle)420 mm (16.5 in)

Performance

Travel speed forward, gears 1-4 (938G, standard tires)7.0 / 12.7 / 21.9 / 35.9 km/h (4.3 / 7.9 / 13.6 / 22.3 mph)
Travel speed reverse, gears 1-3 (938G, standard tires)7.0 / 12.7 / 21.9 km/h (4.3 / 7.9 / 13.6 mph)
Travel speed, 938G Series IItop forward speed reported near 38.9-39.0 km/h (24.2 mph), reverse near 23.3 km/h (14.5 mph); tire and gearing dependent
Transmissioncountershaft power shift, four speeds forward and three reverse, automatic shift capability with quick gear kickdown
Breakout force, general-purpose bucket (938G)approximately 11,235 kg (24,770 lb); bucket-dependent
Breakout force, 938G Series IIapproximately 12,848 kg (28,326 lb); bucket-dependent
Hydraulic cycle time (938G)raise 6.0 s, dump 1.4 s, lower empty with float down 2.8 s, total cycle 10.2 s
Implement pump output (938G)163 L/min (43 gpm) at 2597 rpm, relief valve setting 24,800 kPa (3600 psi)
Steering pump output and relief (938G)102 L/min (27 gpm) at 2597 rpm; relief valve setting 22,800 kPa (3306 psi)

Service capacities (summary)

Fuel tank254 L (67 gal)
Cooling system52.5 L (13.8 gal)
Engine oil (crankcase, with filter)20 L (5.3 gal)
Transmission30 L (7.9 gal)
Differentials and final drives, front24 L (6.3 gal)
Differentials and final drives, rear27 L (7.1 gal)
Hydraulic system, including tank90 L (23.8 gal); hydraulic tank alone holds 55 L (14.5 gal)

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

938G fluids & capacities

SystemCapacityRecommended fluid
Engine crankcase (with filter)approx. 20.0 L (5.3 US gal) on early 938G (Cat 3126 DITA engine); approx. 31.0 L (8.2 US gal) reported for 938G Series II (Cat 3126B ATAAC engine) — varies by series/configurationCat DEO (Diesel Engine Oil) SAE 15W-40 multigrade; ambient range about -9.5°C to 50°C (15°F to 122°F). Cat DEO 10W-30 or DEO-ULS as alternate grades; for cold-climate starts Cat Arctic DEO SYN (synthetic, wider low-temp range) is the cold-weather pick
Cooling systemapprox. 48.1 L (12.7 US gal) to 52.5 L (13.9 US gal) — varies by series/configurationCat ELC (Extended Life Coolant), premixed or concentrate blended to a 50/50 ratio with water for standard service; higher concentrate ratio used where extreme low-ambient protection is required. ELC is the long-life, no-SCA-top-up option; conventional Cat DEAC coolant with supplemental coolant additive is the alternate if ELC is not in service
Fuel tank254 L (67.1 US gal)No. 2-D diesel fuel per Cat fuel specification; low-sulfur/low-temperature blends as ambient conditions require
Transmission (powershift, powertrain compartment)approx. 30.0-30.3 L (7.9-8.0 US gal)Cat TDTO (Transmission/Drive Train Oil); grade selected by ambient temperature per Cat's viscosity chart — SAE 10W for cold conditions, SAE 30 for temperate range (about 0°C to 35°C), SAE 50 for hot climates. Cat TDTO-TMS (synthetic, wide-range) is the option where one fill must cover a broad seasonal temperature swing (down to roughly -40°C)
Front axle / differential and final driveapprox. 24.0 L (6.3 US gal) on early 938G; approx. 30.3 L (8.0 US gal) reported for 938G Series II — varies by series/configurationCat TDTO, SAE 50 typical fill grade, adjusted colder/lighter per ambient temperature the same as transmission/final drive guidance
Rear axle / differential and final driveapprox. 27.0 L (7.1 US gal) on early 938G; approx. 32.2 L (8.5 US gal) reported for 938G Series II — varies by series/configurationCat TDTO, SAE 50 typical fill grade, adjusted colder/lighter per ambient temperature the same as transmission/final drive guidance
Hydraulic tank (reservoir only)approx. 55.0 L (14.5 US gal) on early 938G; approx. 76.0 L (20.1 US gal) reported for 938G Series II — varies by series/configurationCat HYDO Advanced 10 (SAE 10W hydraulic oil), formulated for a wide operating-temperature range; Cat TDTO is the accepted alternate on machines where the implement hydraulic and drive-train circuits share fluid
Hydraulic system total (tank plus lines, cylinders, cooler)approx. 90.0-90.1 L (23.8 US gal) — consistent across 938G and 938G Series IICat HYDO Advanced 10; select viscosity grade for ambient temperature per Cat's hydraulic oil chart, same product family as the tank-only fill
Grease (chassis lubrication points, spec only)not a refill volume — service-interval item, quantity per grease point not specified in OMM capacity chartCat Multipurpose Grease (MPGM) NLGI 2 for normal service, roughly -20°C to 40°C (-4°F to 104°F); NLGI 1 or 0 grades, or Cat's arctic-rated grease, for sustained sub-zero climates

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

Caterpillar 938G maintenance schedule

Service intervalTasks
Every 10 h
  • Check engine oil and coolant level before the first start of the day (10h).
  • Walk around the machine daily and check for fuel, oil, coolant, and hydraulic leaks (10h).
  • Drain the fuel water separator and check the air filter service indicator daily (10h).
  • Grease the loader linkage, bucket pins, and center articulation joint weekly (50h).
  • Check tire condition, inflation pressure, and wheel nut torque weekly (50h).
  • Clear debris from the radiator and hydraulic oil cooler fins weekly (50h).
Every 250 h
  • Change engine oil and the engine oil filter.
  • Replace the primary and secondary fuel filters.
  • Check transmission oil level and transmission charge pressure.
  • Inspect the alternator drive belt for wear and correct tension.
  • Check coolant level and condition.
  • Check service brake accumulator pressure and pedal travel.
Every 500 h
  • Change the transmission oil filter and pull a transmission oil sample.
  • Change the hydraulic system oil filter(s).
  • Check front and rear axle/differential oil level.
  • Inspect king pins and bucket linkage pins and bushings for play.
  • Pull S·O·S samples on engine oil, coolant, hydraulic oil, and axle oils.
  • Check battery, starter, and alternator connections for corrosion and tightness.
Every 1,000 h
  • Change front and rear axle/differential oil.
  • Change transmission oil (full drain and refill).
  • Check engine valve lash and adjust as needed.
  • Review oil-analysis trends on the transmission clutch packs and torque converter circuit.
  • Inspect the turbocharger for shaft play and check for boost leaks.
  • Inspect articulation joint and center-hinge bearings for wear.
Every 2,000 h
  • Change hydraulic system oil.
  • Replace the hydraulic tank breather.
  • Inspect the quick-coupler hydraulic circuit and pins (IT38G configuration) for wear.
  • Check engine, radiator, and cab mounts for cracking or bushing wear.
  • Inspect ROPS/FOPS structure, mounting bolts, and seat belt condition.
  • Inspect final drive and axle planetary housings for leaks or gear wear.
Every 4,000 h
  • Change hydraulic oil filter housings and inspect hydraulic pump case-drain flow.
  • Inspect torque converter and powershift clutch packs based on oil-analysis wear trend.
  • Reassess loader-linkage pin bores for elongation and plan reboring or sleeving if worn.
  • Check axle planetary carrier bearings and differential lock (limited-slip) condition.
Every 6,000 h
  • Replace extended-life coolant (ELC) and flush the cooling system.
  • Perform a major inspection of the engine top end (liners, pistons, injectors) and schedule overhaul work indicated by oil-analysis trends.
  • Rebuild or replace the torque converter and powershift clutch packs if wear trend supports it.
  • Inspect and rebuild axle differential carriers and planetary gear sets as needed.

Servicing the 938G beyond the schedule

Predictive Maintenance & Fluid Analysis

Run S·O·S fluid sampling on the Cat 3126/3126B engine oil, the electronic-planetary powershift transmission oil, and front/rear axle oil at every scheduled interval to catch wear trends before failure. Watch transmission charge pressure - a reading drifting toward the low end of the normal range signals valve-body or solenoid wear before shifting problems show up. On 938G Series II machines, track HEUI-system oil condition for fuel dilution and soot loading. Sample hydraulic oil and extended-life coolant on the same rotation to plan filter and fluid changes around real wear data, not just elapsed hours.

Corrective & Common Repairs

Most 938G downtime traces to the transmission and hydraulics. Delayed or single-gear engagement usually points to worn control solenoids or valve-body wear inside the electronic powershift; check charge pressure before swapping parts. Hydraulic vane pumps run hot and lose output under sustained high-load digging, so confirm case-drain flow before assuming a cylinder fault. Rear limited-slip differential noise on turns calls for an oil sample before teardown. On IT38G toolcarrier units, inspect coupler pins and hydraulic lines often - they cycle more than a standard bucket linkage.

Overhaul & Rebuild Points

Plan major work around the 3126/3126B top end (liners, pistons, turbocharger), the powershift clutch packs, and the front/rear axle planetaries and differential carriers - all wear with hours and duty cycle rather than a fixed schedule. Loader-linkage and bucket pin bores elongate under repeated cycling; welding, reboring, and sleeving the housings restores fit better than replacing pins and bushings alone. During any driveline rebuild, check the rear axle trunnion oscillation bearings, since they carry the articulation load and are easy to miss during a routine axle service.

Seasonal & Environment Servicing

In cold climates, use the block heater ahead of starts near or below freezing, verify extended-life coolant protects to about -37°C (-38°F), and confirm glow plug or air-inlet heater function before winter. In quarry or aggregate dust, shorten air filter and radiator/hydraulic-cooler cleaning intervals and keep the cab pressurizer filter serviced to protect Series II electronics. On wet or muddy sites, grease king pins, the center hinge, and bucket linkage more often than standard, and check axle breathers for mud intrusion that traps pressure and pushes seals.

938G fault codes & troubleshooting

CodeMeaningLikely causeWhat to do
CID 0041 FMI 03/04 ("41-3"/"41-4")Sensor supply voltage circuit reads above normal (03) or below normal (04). This is the shared reference supply that feeds several Power Train ECM sensors.A shorted or grounded signal wire on one of the sensors sharing this supply drags the whole circuit down; corroded pins or a failing Power Train ECM supply stage are secondary causes.Check the reference supply voltage at the ECM connector first. Because this circuit is shared, isolate sensors one at a time on the harness rather than replacing parts, since a single short can post several unrelated-looking codes at once.
CID 0070 FMI 03/04Parking brake switch circuit voltage is out of the expected range.Misadjusted or worn parking brake switch, chafed harness near the brake linkage, or a corroded connector.Check switch adjustment and continuity in both brake positions, then inspect the harness routing at the brake assembly before condemning the switch.
CID 0177 FMI 03/04Transmission oil temperature sensor signal is above or below the valid voltage range.Failed sensor element, open or shorted sensor wiring, or a corroded connector at the sensor.Compare sensor resistance to spec at a known oil temperature, inspect the wiring and connector, and replace the sensor if it reads out of range.
CID 0190 FMI 02Engine speed signal received by the Power Train ECM is erratic, intermittent, or incorrect.Damaged or loose wiring in the data link run between the engine ECM and the Power Train ECM, a marginal data link connector, or an engine-side speed/timing sensor problem feeding bad data across the link.Inspect the data link wiring and connectors between the engine and powertrain ECMs first, confirm the engine ECM itself is reporting a stable rpm signal, then check the engine speed sensor air gap.
CID 0248 FMI 12The Cat Data Link (the communication bus tying the engine ECM, Power Train ECM, and other modules together) reports a bad device or component.Corroded or damaged data link wiring, a loose splice connector, or a failed module holding the bus down.Inspect the data link harness and connectors for corrosion or chafe, confirm every module on the bus powers up normally, and check for proper wiring continuity before swapping ECMs.
CID 0368 FMI 03/04Transmission auto/manual rocker switch circuit voltage is out of the valid range.Worn or failed rocker switch contacts, chafed wiring near the steering column/console, or a corroded connector.Test switch continuity in both positions, inspect harness routing at the switch, and replace the switch if it fails the continuity check.
CID 0672 FMI 01Torque converter output speed sensor signal reads below the normal operating range.Incorrect sensor air gap, a damaged tone wheel/reluctor, or an open/shorted sensor circuit.Check sensor mounting and air gap first, inspect wiring continuity end to end, and replace the sensor if the signal stays out of range with the engine running.
CID 0793/0794 FMI 03/04Pressure switch monitoring the primary (0793) or secondary/backup (0794) steering oil supply reads outside the valid range; this can trip the secondary steering alarm or disable normal steering assist logic.Failed pressure switch, low steering pump output pressure, or a wiring fault at the switch.Verify primary steering pump pressure against spec, check switch operation and wiring, and treat this as a safety-critical fault: confirm the backup steering circuit is functional before returning the machine to service.
CID 1401 FMI 03/05/06/13 (Modulating Valve No. 1, Transmission)Transmission clutch modulating valve solenoid circuit is out of the expected voltage/current range, or the valve is out of calibration (FMI 13).Failed solenoid coil, damaged harness or connector at the valve, or a transmission calibration that was never redone after an ECM or valve replacement.Check solenoid coil resistance and wiring first, run the transmission calibration procedure with the Cat electronic service tool, and replace the valve if coil resistance is out of spec.

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

938G attachments & work tools

General-purpose buckets

Rated capacity runs roughly 2.1-2.8 m3 (2.75-3.7 yd3) heaped, with widths near 2.7-2.8 m (8'9"-9'1"), varies by configuration/series. Long-floor sand-and-gravel buckets are also offered, built with curved side bars, corner guards and replaceable wear plates for abrasive bank and stockpile work.

Side-dump / high-dump buckets

Side-dump buckets let the loader clear material to the side in tight yards while still dumping forward like a standard bucket. High-dump buckets add extra dump clearance for loading over truck sideboards or hoppers.

Pallet forks

Carriage-mounted pallet forks are offered in several tine lengths for this loader class; listings for 938G-fit fork carriages commonly show tines around 1.2 m (48 in). Rated capacity must be checked against the specific carriage and coupler combination used.

Log and lumber forks

Log forks with a top clamp are offered for handling tree-length or cut logs, alongside lumber-handling fork variants, for forestry and mill-yard use with this size of loader.

Ground engaging tools (GET)

Bucket edges and tooth systems are offered in standard and heavy-duty retention designs, letting the same bucket body be tuned for abrasive digging versus lighter loading duty.

Coupler / mounting system

Base machine ships with pin-on (bolt-on) work tool mounting. A factory quick coupler option is available, described as a horizontal pin-lock design; the 938G shares its coupler group with the 928G and IT28G lines. Later in the model's life Cat offered the Fusion coupler, a design that pulls the tool close to the lift arm to keep near pin-on breakout and lift performance while retaining quick-change flexibility; Fusion couplers are cross-listed for both 938G and 938H.

IT38G integrated toolcarrier variant

Cat offered the 938G chassis as the IT38G Integrated Toolcarrier, using a parallel-lift linkage instead of the standard loader Z-bar arm. This geometry favors fork and material-handling work, keeping the load level through the lift cycle, and is documented alongside the standard 938G in shared electrical and hydraulic schematics.

Third (auxiliary) valve / hydraulic kit

An optional third hydraulic valve section is available for actuating a quick coupler locking pin or for running powered work tools. Cat notes the added valve body, extra hydraulic lines and an added in-cab control handle as the practical difference versus the standard two-valve loader circuit.

Ride control

Optional automatic ride control uses a nitrogen-over-oil accumulator in the lift circuit to damp bucket/tool bounce during travel, selectable between Off, On and Auto modes. Recommended when running forks or buckets over rough haul roads.

Waste handling factory arrangement

Cat offered an ex-factory 938G / IT38G Waste Handler arrangement for transfer stations, recycling yards and waste-to-energy sites, adding guarding and screening to limit debris intrusion into machine components. Cat documentation notes guards and modifications differ by arrangement and are not interchangeable between packages, and duty-cycle performance shifts once the extra guarding is fitted.

All 938G assemblies by section

Every catalogued assembly group for the Caterpillar 938G. Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.

Hydraulic System
124-9439 Accumulator Gp-Ride Control
06***35Valve-Gas1
10***06Film-Warning; (High Pressure Cylinder)1
12***39Accumulator Group-Ride Control; -Charged1
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4q-1755 Kit-Ride Control -Custom
10***04Kit-Receptacle; (4-Pin)(Start Switch)1
10***06Film-Warning; (High Pressure Cylinder)1
10***20Harness Assembly1
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2q-7821 Kit-Ride Control -Custom
10***04Housing1
10***04Kit-Receptacle; (4-Pin)(Start Switch)1
10***06Film-Warning; (High Pressure Cylinder)1
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4t-2764 Valve Gp-Relief
3K***60Seal Pilot Manifold On; Seal To Boom Check Valve Drain2
4T***41Spring1
4T***64Valve Group-Relief; (Line, Tilt Cylinder Head End)1
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124-8206 Valve Gp-Ride Control
11***32Valve Group1
12***06Valve Group-Ride Control1
13***88Plug-Straight Thread1
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149-2658 Valve Gp-Solenoid
11***43Locknut; (5/16-18-Thd)2
14***05Coil Assem.1
14***11Cartridge Assem.1
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938G serial number reference

The PIN plate on a 938G/938G II sits on the front frame, low on the left (highway) side, behind the front tire near the articulation joint - check the operator's manual diagram if it's hard to spot under paint or grime. On pre-2001 machines the plate shows an 8-character PIN (3-letter prefix plus 5-digit sequence, e.g. 9HS00234); on 2001-and-later machines it's stamped as part of a full 17-character PIN, with the same 3-letter prefix and 5-digit sequence embedded near the end. The prefix identifies the specific model/build series - cross-check it against the machine's build plate data and engine tag rather than assuming from the model name alone.

PrefixIdentifies
4YS938G (first generation) wheel loader
6WS938G (first generation) wheel loader
8RS938G (first generation) wheel loader
9HS938G (first generation) wheel loader
B9Y938G Series II (938G II) wheel loader
CRD938G Series II (938G II) wheel loader
PHN938G Series II (938G II) wheel loader
RTB938G Series II (938G II) wheel loader
MSC938G Series II (938G II) wheel loader

Frequently asked questions

What engine does the Caterpillar 938G use?

It depends on series. The original 938G (1998-2003) uses the Cat 3126 DITA, a turbocharged and aftercooled mechanical unit-injection diesel rated about 118-119 kW (158-160 hp) at the flywheel. The 938G Series II (2003-2008) switched to the electronically controlled Cat 3126B HEUI diesel with ATAAC, rated about 119 kW (160 hp) standard and up to 134 kW (180 hp) with power management engaged.

What is the operating weight of the Caterpillar 938G?

Operating weight runs about 13.1-13.2 t (28,900-29,100 lb) for the standard 938G and closer to 14.0 t (30,800 lb) for the 938G Series II. Exact weight varies by configuration - standard loader versus IT38G integrated toolcarrier, counterweight, tire choice, and attachment fitted.

What replaced the Caterpillar 938G?

Within the same generation, the 938G was updated to the 938G Series II in 2003 with an electronic engine and electro-hydraulic coupler controls. As a full model-line replacement, Caterpillar moved this size class to the 938H next, then later to the 938K and 938M.

What 938G owners discuss

Why does the transmission on a 938G shift smoothly cold but get rough or hesitate once it warms up?
This is a widely reported pattern on the countershaft powershift transmission, not a one-off. Typical description: shifts are clean while oil is cold, then get rough between gears (often every gear except one) as the oil heats up, sometimes with a jerk-forward-then-reverse when changing direction, or a pause before engaging if the shift lever moves quickly. Root causes owners have traced it to: worn or glazed clutch discs and plates, a broken or weak spring in a clutch pack, aluminum control-valve spools sticking as clearances change with heat, and aerated transmission oil. Repair path that has worked for owners: rebuild the affected clutch pack (discs, plates, seals), clean the magnets and screen in the suction filter (fine metal shed from worn friction material collects there), and check the solenoid shift valves - each clutch has its own solenoid, so an intermittent one is usually found by swapping it with a known-good unit. Because a direction change that hangs or jerks under load can catch an operator off guard, have your dealer verify clutch pressures at each solenoid before the machine goes back to work.
What's the story with the 938G's diesel engine, and does it differ by series?
The original 938G (built roughly 1998-2003) runs the Cat 3126 DITA (direct-injection, turbocharged, aftercooled). The 938G Series II (roughly 2003-2008) moved to the 3126B, built around HEUI (hydraulic electronic unit injection) with ATAAC cooling and a higher rated output to meet Tier 2 emissions; it also added an on-demand cooling fan and stretched the oil-change interval to 500 hours on CH-4 oil. Owners of 3126-family HEUI engines consistently flag the same weak points regardless of chassis: hard-start or no-start traced to a weak high-pressure oil pump not building enough pressure to fire the injectors, injector O-rings failing and letting fuel migrate into the crankcase oil, and rough idle or misfire from worn or out-of-time injectors, which after replacement need to be resynchronized with a dial-gauge procedure or the engine can knock or run away. None of this is unique to the loader - it's the same HEUI behavior reported on 3126-powered trucks - but it shows up on 938G reports just as often. A well-maintained 3126 is widely reported to run into the 15,000-20,000 hour range before a major inframe, though that number tracks oil-change discipline and duty cycle more than raw hours.
What do owners say about the hydraulic/implement system on the 938G?
Consensus is that sluggish or lazy lift-arm and bucket response is usually fluid level, a clogged suction screen, or air in the circuit before it's a pump problem. A whining pump is most often linked to cavitation from low fluid or a restricted suction side rather than internal pump failure. On the vane-type implement pump used on the 938G, owners report the vanes are vulnerable to heat damage under sustained high-load work if the system runs hot or low on fluid. A recurring troubleshooting note: a suspect pump can check out fine on a light or no-load bench test and then reproduce the exact same fault once it's back under real working load, so a clean bench test doesn't clear it. When a pump is replaced after a failure, the circuit needs a thorough flush first - leftover metal or debris from the failed pump is a commonly cited cause of a brand-new pump failing the same way almost immediately.
Why do 938G brakes get described as spongy or soft, and is that dangerous?
The service brakes run off a twin oil-charged accumulator circuit, one accumulator per axle circuit, charged by the hydraulic system while the engine runs. A soft or spongy pedal is most often traced to a worn dump-valve seal inside the accumulator letting fluid bypass, or to the nitrogen precharge drifting low over time. The standard field check: run the engine a couple of minutes to let the accumulators fully charge, shut it down, then pump the brake pedal repeatedly and count how many strokes it takes before the low-brake-pressure warning lights - the O&M manual specifies a minimum number of pumps before that warning should trigger. Fewer pumps than spec points to a weak accumulator charge or an internal leak. Because this is a nitrogen-precharged, pressure-accumulator brake circuit feeding the only service brakes on the machine, treat any accumulator recharge or seal work as safety-critical and have your dealer verify precharge pressure and warning-light timing before the machine returns to service.
What electrical or sensor problems come up most on the 938G?
Community experience points less at sensor failure and more at wiring harness condition. A recurring theme is an intermittent transmission fault or gear-warning light traced back to harness chafing, corrosion, or a loose connector - especially in the steering-column area, where the harness flexes every time the machine articulates. A simple wiggle test on the harness while watching for the fault to flash is the usual first diagnostic step. Since each transmission clutch runs off its own solenoid valve, a no-engage or stuck-gear complaint is commonly narrowed down by cross-swapping solenoids or touching a screwdriver tip to an energized solenoid to confirm the coil is pulling. When a diagnostic tool flags a sensor circuit as reading voltage above or below normal, owners note that's an electrical-circuit fault, not proof the sensor itself is bad - a corroded connector or a lost ground will throw the identical code.
How much wear should I expect at the center articulation joint and bucket linkage, and what drives it?
The articulation hitch and Z-bar bucket linkage are grease-fed pin-and-bushing joints, and the consensus is blunt: missed greasing is the number-one cause of premature pin wear, where the pin and bushing gall and effectively friction-weld together. Recommended interval is roughly every 8-10 hours of work, tightened to about every 4 hours in wet or sandy ground. A squeal, grind, or felt looseness at a pin joint under load is treated as a wear signal to inspect immediately, not something to grease away. On the center hitch bearing specifically, owners chasing play have shimmed the upper and lower hitch bearing caps to take up clearance rather than replacing the full bearing assembly. Because this joint carries the entire articulated frame and affects steering control, have your dealer verify remaining play and shim thickness before putting a reshimmed hitch back to work.
What should I check before buying a used 938G?
In rough priority order, based on what experienced buyers and mechanics look at: pull whatever service or oil-sample history is available - engines with disciplined oil-change intervals in dusty conditions are reported to run well beyond what the hour meter alone would suggest, so paperwork matters as much as hours; run the accumulator brake test cold with the engine off and count pump strokes to the warning light; cycle the transmission through the gears cold, then again once the oil is hot, checking for the warm-shift jerk or hesitation pattern that's common on this transmission; check the articulation hitch and bucket linkage pins for play and look at whether the center hitch bearing caps have ever been shimmed; note engine starting behavior both hot and cold, since a hard or delayed start points at a tired HEUI high-pressure pump; look for oil-in-coolant or fuel-in-oil signs, which on 3126-family engines usually trace to failed injector O-rings; and confirm which engine and series the machine actually has (3126 DITA versus 3126B), since oil-change intervals, power rating, and available parts differ between them. Have your dealer pull a full fault-code and service history from the ECM before you finalize any purchase.

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

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