Overview#
The Kohler 45REOZT4 is a 40-kilowatt standby (36 kW prime) EPA Tier 4 Final diesel mobile trailer generator powered by a Kohler KDI 2504 TCR engine at 1800 RPM. The 4-cylinder, 2.5-liter KDI engine achieves Tier 4 Final compliance via cooled EGR and Diesel Oxidation Catalyst without requiring a DPF, keeping maintenance simple and eliminating forced-regen events during critical deployments.
The 45REOZT4 features a brushless wound-field alternator with Kohler's PowerBoost excitation system and the Decision-Maker 3500 paralleling controller, allowing multiple units to be synchronized for larger temporary power installations. A 293-liter (77-gallon) subbase fuel tank provides a minimum 24-hour run time at prime rating. The standard single-axle DOT/TC-compliant trailer with electric brakes and battery-backup breakaway makes the unit towable by a standard pickup truck. Sound level is rated at 68 dB(A) at 7 meters, one decibel above the smaller 35REOZT4.
The unit ships with 125% oil/coolant containment and 110% secondary fuel containment, satisfying most environmental permitting requirements for temporary generator installations without additional secondary containment measures.
Specifications#
| Spec | Value |
|---|---|
| Standby Power | 40 kW |
| Prime Power | 36 kW |
| Voltage | 120/208V, 120/240V, 277/480V, 347/600V |
| Frequency | 60 Hz |
| Engine | Kohler KDI 2504 TCR |
| Cylinders | 4 inline |
| Displacement | 2.5 L (152.5 cu. in.) |
| Aspiration | Turbocharged |
| Emissions | EPA Tier 4 Final (nonroad) |
| RPM | 1800 |
| Fuel | Ultra Low Sulfur Diesel / HVO / RD |
| Cooling | Liquid (unit-mounted radiator) |
| Fuel consumption — 100% load | 3.3 gph (standby) |
| Fuel consumption — 75% load | 2.5 gph (standby) |
| Fuel tank | 77 gal (293 L) — 24 hr minimum runtime |
| Sound level | 68 dB(A) @ 7 m (prime, full load) |
| Dimensions (L x W x H) | 86" x 40" x 63.9" |
| Controller | Decision-Maker 3500 |
Service & Maintenance#
Kohler's published maintenance schedule for the 45REOZT4 / KDI 2504 TCR engine:
| Service | Interval |
|---|---|
| Oil and filter change | Every 250 hours or 12 months |
| Fuel filter replacement | Every 250 hours |
| Air filter inspection/replacement | Every 500 hours |
| Coolant flush | Every 2,000 hours or 3 years |
| Load bank test | Every 12 months (NFPA 110 requirement) |
| Major overhaul | Every 8,000 hours |
Kohler recommends Genuine oil (API CJ-4 or ACEA E6–E9) and genuine filters. For units deployed at construction sites or events where fuel quality is variable, we recommend a fuel sample test at each scheduled service to catch microbial growth or water contamination early.
Common Failure Modes#
The 45REOZT4's Tier 4 aftertreatment system is the leading source of fault codes in this series. Back-pressure and oxidation catalyst monitoring can trigger derate warnings if the aftertreatment system is not kept clean — particularly on units operated at very light loads for extended periods. Running the unit at 50% or higher load whenever possible significantly extends aftertreatment service life.
Fuel quality degradation is the second most common issue. Injector fouling from stale or contaminated diesel presents as hard starting, rough running, and elevated smoke. The KDI 2504 TCR common-rail system is sensitive to fuel cleanliness; primary 5-micron filtration is standard but fuel polish is recommended for tanks stored over 90 days.
Battery failures are common on standby units: a single 12V 925 CCA battery powers starting, and battery charger function should be verified at each service visit.
Our service experience#
OnPoint Generators provides installation, maintenance, load bank testing, and emergency service for Kohler industrial generators throughout Northern California and the Central Valley. The 45REOZT4 is a step up from the 35REOZT4 for applications needing 40 kW of reliable mobile power. The KDI 2504 TCR engine shares tooling and service procedures with the smaller 3-cylinder KDI 1903 TCR, which means our technicians carry compatible parts for both models on every service truck serving the REOZT4 fleet.
FAQ#
What is the standby rating of the Kohler 45REOZT4?#
The 45REOZT4 is rated at 40 kW standby (50 kVA at 0.8 PF three-phase) at 120/208V. Prime power is 36 kW. The "45" in the model name follows Kohler's older naming convention. All ratings are per Kohler spec sheet G5-413.
Is the 45REOZT4 a mobile or stationary generator?#
The 45REOZT4 is a trailer-mounted mobile generator, EPA Tier 4 Final certified for nonroad applications. A single-axle DOT/TC-compliant trailer with electric brakes is available as an option, making it towable by a standard pickup truck.
Does the 45REOZT4 require a DPF?#
No. The 45REOZT4 meets EPA Tier 4 Final without a Diesel Particulate Filter using cooled EGR and a Diesel Oxidation Catalyst. This eliminates forced-regen downtime and simplifies maintenance compared to systems that require active DPF regeneration.
What is the sound level of the Kohler 45REOZT4?#
Per Kohler published specifications, the 45REOZT4 is rated at 68 dB(A) log average at 7 meters (23 feet) with full load at the prime rating.
