500 kW standby / 435 kW prime · Natural Gas · Liquid-cooled
490-500 kW natural gas industrial standby generator with Siemens engine and Brushless Permanent-Magnet Pilot Exciter alternator. Large commercial and industrial backup power.
The Kohler 500REZK is a 490-500 kW natural gas industrial standby generator. Unlike most Kohler gaseous units, the 500REZK is powered by a Siemens engine rather than a Kohler engine, and it uses a Brushless Permanent-Magnet Pilot Exciter alternator. The unit is certified for both EPA stationary emergency and non-emergency operation, making it suitable for prime power applications as well as standby duty.
Rated 430-435 kW prime, the 500REZK is sized for large commercial facilities, healthcare campuses, and light industrial operations that require high-capacity natural gas backup without on-site diesel fuel storage.
The 500REZK is a less common unit in our territory due to its size class, but we service it at larger commercial and healthcare sites. The Siemens engine requires familiarity with a different service platform than the Kohler KG-series engines, so technicians should reference Siemens-specific documentation for engine maintenance intervals and procedures.
Lock the enclosure, fuel system, transfer switch, and add-ons — we'll confirm pricing, availability, and lead time within one business day. Prefer a free-form quote? That option is still here.
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
5,250,000 BTU/hr≈ 5250.0 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 Kohler 500REZK 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 4000 hours
Air filter
Every 1000 hours
Spark plugs
Every 1000 hours
Major overhaul
≈ 12,000 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
Spark plugs / ignition
Misfire, cylinder dropout, rough running under load
1,000+
minor
Gas train / pressure regulator
Hard starting, gas pressure fault, no-start condition
8,000+
moderate
Turbocharger seals
Oil carryover, blue smoke, boost pressure loss
12,000+
moderate
Battery (starting)
Slow crank, failed exercise
8,760+
minor
Frequently Asked Questions
What is the standby power rating of the Kohler 500REZK?
The 500REZK is rated 490-500 kW standby (430-435 kW prime) at 60 Hz depending on voltage configuration. It is a large-format natural gas industrial generator.
What engine is in the Kohler 500REZK?
The 500REZK uses a Siemens industrial gas engine, not a Kohler engine. This is one of the few Kohler generator sets that uses a third-party engine platform.
Does the 500REZK run on propane?
No. The 500REZK is natural gas only. Unlike the KG series which supports dual-fuel NG/LPG, the 500REZK is certified exclusively for natural gas operation.
