Overview#
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.
Cummins QSG12 engine and variable-speed cooling#
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.
Our service experience#
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.
