Kohler · REOZ Series (Diesel Commercial Standby)

Kohler 40REOZK4

40 kW standby / 36 kW prime · Diesel · Liquid-cooled

40 kW Tier 4 Final diesel commercial standby generator. Kohler-powered diesel with EPA Tier 4 Final emissions compliance for commercial and institutional applications.

Kohler Kohler 40REOZK4 generator — specifications and details
Standby power
40 kW / 36 kW prime
Voltage options
120/208V, 277/480V, 120/240V
Frequency / Phase
60 Hz · 1/3-phase
Engine
Kohler KDI 2504 TCR · 2.5L
EPA / Emissions
Tier 4 Final
CommercialHealthcareGovernment
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Overview#

The Kohler 40REOZK4 is a 40-kilowatt EPA Tier 4 Final diesel commercial standby generator powered by a Kohler diesel engine at 1800 RPM. It achieves Tier 4 Final compliance through cooled exhaust gas recirculation (EGR) and a diesel oxidation catalyst (DOC). The unit is certified for both stationary emergency and non-emergency applications and features a sound-attenuating housing rated at 67 dB(A) at 7 meters, integrated environmental containment, and an electronic isochronous governor.

Our service experience#

OnPoint services Tier 4 Final diesel generators across Northern California, where Bay Area air quality rules frequently require Tier 4 certification. The 40REOZK4 adds cooled EGR and DOC components that require periodic inspection during annual maintenance.

Engineering specifications

Physical

Length
86 in
Width
40 in
Height
63.9 in
Wet weight
3,180 lb

Acoustic

Sound @ 7m, full load
68 dBA
Enclosure
Sound-attenuated

Fuel system & runtime

Integral fuel tank
77 gal
Fuel use @ full load
3.3 GPH
Fuel use @ 75% load
2.5 GPH
Fuel use @ 50% load
1.7 GPH

Photos

Kohler 40REOZK4 — product photo

Documents & downloads

Spec sheets & manuals

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Estimate runtime for the Kohler 40REOZK4

Adjust load percent and tank size to estimate runtime. Pre-filled with this model's spec where available.

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Estimated runtime

30.2 hours(1.3 days)

Fuel consumption ≈ 2.55 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 Kohler 40REOZK4 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 2000 hours
Air filter
Every 500 hours
Fuel filter
Every 250 hours
Major overhaul
≈ 8,000 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.

ComponentSymptomTypical hoursSeverity
DPF (Diesel Particulate Filter)Regen warning, back-pressure fault, power derate4,380+moderate
Fuel quality / degradationInjector fouling, hard starting, reduced power output4,380+moderate
Battery (starting)Slow crank, failed exercise, low voltage alarm8,760+minor

Frequently Asked Questions

What makes the 40REOZK4 different from the 40REOZK?
The 40REOZK4 is the EPA Tier 4 Final variant with cooled EGR and diesel oxidation catalyst for stricter emissions compliance. It is certified for both stationary emergency and non-emergency applications.
What is the sound level of the 40REOZK4?
Per Kohler specifications, the 40REOZK4 is rated at 67 dB(A) at 7 meters at full load with the sound-attenuating housing.
Does the 40REOZK4 include fuel containment?
Yes. The unit includes a 125% environmental containment basin for oil/coolant and a 110% secondary fuel containment tank with UL 142 listed subbase fuel tank for 24-hour minimum runtime at prime rating.

Compatible equipment

Transfer switches

More in the REOZ Series (Diesel Commercial Standby)

Kohler's diesel commercial standby series — 10 to 510 kW, John Deere and Kohler engines, built for life-safety loads.

View all 33models in this series →

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