The Caterpillar G3406 is a 300 kW standby natural gas generator built on the turbocharged 14.6L G3406 TA inline-6. No diesel fuel storage required — ideal for hospitals, campuses, and commercial facilities.
The Caterpillar G3406 is a 300 kW standby natural gas generator built on the 14.6-liter G3406 TA — the spark-ignited, gaseous-fuel version of Cat's iconic 3406 diesel block. As a natural gas unit, the G3406 eliminates on-site diesel fuel storage concerns, making it an attractive choice for hospitals, campuses, and commercial facilities in areas where diesel storage permitting is challenging or where uninterrupted gas supply is assured.
The G3406 complies with EPA 40 CFR 60 Subpart JJJJ for stationary spark ignition engines and holds NFPA 110 Level 1 certification. Though now a legacy product, its shared architecture with the diesel 3406 means the parts ecosystem is broad and technicians familiar with the diesel variant can readily transition to the gas platform.
We have maintained G3406 units at hospital and campus facilities across the Bay Area. The gas engine's spark ignition system requires additional attention during annual PM — distributor, plugs, and ignition timing — beyond what a diesel technician would perform on the 3406 diesel. We advise clients to engage technicians with specific Cat gaseous engine experience and to keep a set of ignition components on-site given the legacy parts cadence.
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Adjust load percent and tank size to estimate runtime. Pre-filled with this model's spec where available.
Estimate runtime on this tank
Fuel demand at 75% load
3,150,000 BTU/hr≈ 3150.0 cf/min @ 1,000 BTU/cf
On utility natural gas the runtime is generally unlimited provided the supply line and meter can deliver this BTU/hr at the engine's required inlet pressure (typically 5–14" WC residential, up to 5 psi commercial). Confirm against the OEM's published fuel-pressure spec.
Service intervals
Manufacturer-recommended intervals for the Caterpillar G3406 under standby duty. Field intervals may differ based on load profile, ambient conditions, and fuel quality.
Oil & filter
Every 250 hours or 12 months
Coolant change
Every 4000 hours
Air filter
Every 1000 hours
Spark plugs
Every 1500 hours
Major overhaul
≈ 15,000 hours
Load bank test
Every 12 months
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
Turbocharger
Loss of power, excessive smoke under load
12,000+
moderate
Spark plugs / ignition
Misfire at load, rough running
1,500+
minor
Charge air cooler
Reduced power output, elevated intake temps
10,000+
moderate
Battery
Failed to start during outage
8,760+
minor
Frequently Asked Questions
What fuel does the Caterpillar G3406 use?
The G3406 runs on natural gas, using the turbocharged-aftercooled G3406 TA spark-ignited engine — the gaseous-fuel variant of Cat's well-known 3406 diesel block.
What compliance standards does the G3406 meet?
The G3406 meets EPA 40 CFR 60 Subpart JJJJ (stationary spark ignition engines), is UL 2200 listed, and is NFPA 110 Level 1 compliant for life-safety standby applications.
Is the G3406 still supported by Cat?
The G3406 is a legacy platform. Factory engineering support is limited, but parts are available through Cat dealers and aftermarket suppliers. Facilities with existing G3406 installations should plan for a long-term transition strategy while maintaining current units under a structured PM program.
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