The Cummins QSK23 (C800 D5) is an 800-kilowatt standby diesel generator built on a 23-liter inline-6 QSK engine — a purpose-built high-output platform that occupies the upper end of the single inline-6 power range. At 800 kW standby and 725 kW prime, the QSK23 covers large hospitals, industrial facilities, major campus standby, and serves as a cost-effective building block for multi-unit paralleling arrays below the 1250 kW threshold.
The 23L inline-6 configuration offers high power density in a physically manageable package compared to V12 and V16 alternatives at higher power levels, with the same QSK platform reliability and Cummins MCRS fuel injection system.
The QSK23 is the right choice for single-unit hospital and large campus standby in the 800 kW range. Our service program for these units emphasizes fuel quality management, turbocharger inspection, and load bank testing — at 800 kW, a marginal turbo or degraded fuel will show up under full-load test conditions before it causes a problem during an actual outage.
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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
Estimated runtime
4.6 hours(0.2 days)
Fuel consumption ≈ 43.20 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 Cummins QSK23 under standby duty. Field intervals may differ based on load profile, ambient conditions, and fuel quality.
Oil & filter
Every 500 hours or 12 months
Coolant change
Every 6000 hours
Air filter
Every 1000 hours
Fuel filter
Every 500 hours
Major overhaul
≈ 24,000 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
Fuel quality (standby degradation)
Injector fouling, filter clogging, hard starting
4,380+
moderate
Turbocharger(s)
Reduced power, excessive smoke, turbo noise
18,000+
moderate
Starting system (24V battery banks)
Slow crank, failed start requirement
8,760+
minor
Frequently Asked Questions
Where does the QSK23 fit in the QSK lineup?
The QSK23 is an inline-6 platform (vs. the V12/V16 of the QSK38/50/60) occupying the 700–800 kW class. It bridges the gap between the QSK19 (700 kW) and QSK38 (1250 kW), providing a cost-effective single-engine solution for facilities in the 750–800 kW standby range before stepping up to the more complex and expensive V12 platforms.
What is the 4160V option used for?
The 4160V medium-voltage alternator option allows the QSK23 to connect directly to a 4.16 kV distribution system without a step-up transformer. This is common in large hospitals, industrial facilities, and campuses with established 4160V distribution infrastructure — eliminating transformer losses and a maintenance item.
Is the QSK23 suitable for NFPA 110 Level 1 applications?
Yes. The QSK23 with its UL 2200 listing and compliance with NFPA 110 Level 1 requirements is appropriate for healthcare and other life-safety applications when properly installed with compliant ATS, fuel systems, and transfer time verification.
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