The Doosan G400 delivers 340 kW of prime power from a Cummins QSG12 11.8-liter engine — a Tier 4 Final unit that effectively replaces the legacy Tier 2 G450 in the current lineup. The 470-gallon integral fuel tank and variable-speed cooling fan support extended runtime on demanding construction and temporary power applications.
At 15,450 lbs, the G400 fills the large-frame portable class between the G325 (267 kW) and G570 (456 kW). Also sold as the Bobcat PG400.
The G400 is powered by the Cummins QSG12, an 11.8-liter turbocharged-aftercooled inline-6 that represents a significant step up in displacement from the QSL9 in the G325. The QSG12 is a proven platform used across multiple generator brands at the 300-400 kVA class, ensuring wide parts availability and standardized service procedures.
The variable-speed cooling fan adjusts fan speed based on coolant temperature rather than running at full speed continuously. This reduces parasitic power loss, lowers fuel consumption at partial loads, and decreases noise levels when the engine is not under full thermal load — a noticeable advantage on extended operations where the generator may cycle between partial and full load.
OnPoint services Cummins QSG12-powered generators across Northern California. At this power level, the Cummins engine is the dominant service consideration — and the QSG12 is well-supported through multiple Bay Area Cummins distributors. The 500-hour oil change interval and standard Cummins filtration make the G400 straightforward to maintain. For operators transitioning from the legacy Tier 2 G450 to the Tier 4 Final G400, the main service difference is the addition of aftertreatment components (DOC, DPF, SCR) that require periodic attention. We recommend maintaining load above 30% to ensure proper DPF regeneration on extended operations.
Engineering specifications
Physical
Length
241 in
Width
83 in
Height
115 in
Wet weight
15,450 lb
Fuel system & runtime
Integral fuel tank
470 gal
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Tell us about the application — kW, voltage, application, install timeline — and we'll respond within one business day with budgetary pricing, lead time, and any sizing notes.
Adjust load percent and tank size to estimate runtime. Pre-filled with this model's spec where available.
Estimate runtime on this tank
Estimated runtime
23.3 hours(1.0 days)
Fuel consumption ≈ 20.20 GPH at 75% load. Estimate based on industry-typical 1800 RPM standby curves (≈0.07 GPH/kW at full load). Actual consumption varies by engine, ambient temperature, fuel quality, and tuning.
Service intervals
Manufacturer-recommended intervals for the Doosan G400 under standby duty. Field intervals may differ based on load profile, ambient conditions, and fuel quality.
Oil & filter
Every 500 hours or 12 months
Air filter
Every 500 hours
Fuel filter
Every 500 hours
Major overhaul
≈ 20,000 hours
Common failure modes
What we've seen fail on this platform. Use as a service-planning reference, not a diagnostic — actual failure modes depend heavily on duty cycle and maintenance history.
Component
Symptom
Typical hours
Severity
Fuel filter
Restricted flow, hard starting, power loss under load
500+
minor
Battery
Failed to start or slow cranking after extended storage
4,380+
minor
Coolant hoses
Weeping at clamp connections, slow coolant loss
5,000+
minor
DPF regeneration
Incomplete regen at sustained light loads, power derate warning
2,000+
moderate
Frequently Asked Questions
What is the standby power rating of the Doosan G400?
The Doosan G400 delivers 374 kW standby and 340 kW prime power. It is powered by the Cummins QSG12 11.8-liter engine and features a variable-speed cooling fan for improved fuel efficiency at partial loads. Also sold as the Bobcat PG400.
What engine does the Doosan G400 use?
The G400 is powered by a Cummins QSG12 11.8-liter inline-6 turbocharged-aftercooled diesel engine running at 1,800 RPM. The QSG12 is a proven platform used across multiple generator brands at the 300-400 kVA class, ensuring wide parts availability and standardized service procedures.
What are the service intervals for the Doosan G400?
Oil changes are due every 500 hours or 12 months, whichever comes first. Air filter and fuel filter replacement intervals are 500 hours. Major engine overhaul is specified at 20,000 hours. The G400 includes a full Tier 4 Final aftertreatment system (DOC, DPF, SCR) requiring periodic inspection.
Is the Doosan G400 EPA compliant?
Yes. The G400 is EPA Tier 4 Final compliant. The Cummins QSG12 meets current U.S. emissions requirements with a full aftertreatment system. Operators should maintain load above 30% to support proper DPF regeneration and prevent derating.
How does Doosan compare to CAT at the 400 kVA class?
Both operate in the 400 kVA class with large-displacement Cummins engines. The G400 typically prices 15-30% below CAT while using the proven Cummins QSG12 platform. CAT has broader dealer infrastructure, but the Cummins QSG12 ensures wide independent distributor parts availability.
What control panel does the Doosan G400 use?
The G400 is equipped with Doosan's digital control panel providing auto-start, fault monitoring, voltage/frequency display, runtime tracking, and full aftertreatment status monitoring including DPF soot load, SCR, and DEF level.
Who services Doosan generators in Northern California?
OnPoint Generators services Cummins QSG12-powered generators across Northern California. The QSG12 is well-supported through multiple Bay Area Cummins distributors. For operators transitioning from the legacy Tier 2 G450, we are experienced with Tier 4 Final aftertreatment servicing on the G400.
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