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Kohler 125REZGT Generator Set

The Kohler 125REZGT is a 105 kW (131 kVA) LP/NG standby generator set powered by a Power Solutions International 8.8L Industrial Powertrain engine. It is available at 110/127 V and 208/220 V, 3-phase, 60 Hz and rated 150 A. It holds about 7.6 L (2.0 gal) of oil and 13.7 L (3.6 gal) of coolant. The set measures 3993×1867×2206 mm (157.2×73.5×86.9 in), weighs about 3629 kg (8001 lb) and produces 69 dBA at 23 m. An integrated tank holds 977 L (258.1 gal), roughly 24 hours of runtime. The same 8.8L Industrial Powertrain engine also powers generator sets from Cummins/Onan.

105 kW
Standby
8.8 L
Displacement
7.6 L
Oil capacity
5
Document types

How to read your Kohler serial & model number →

Service parts for the 125REZGT

Grouped by system, with how many of each the parts manual calls for.

Air intake

1 required
GM62308Air filtersee priceAmazon

Prices captured from merchant listings; some links are affiliate links. Confirm against your serial number before ordering.

Specifications

FuelLP/NG
Frequency60.0 Hz
Standby power105 kW
Standby kVA131
Prime power95 kW
EmissionsEPA Certified Prime
ControllerDecision-Maker 3500
Oil capacity7.6 L
Voltage options110/127 V, 139/240 V, 254/277 V, 208/220 V, 240/415 V, 440/480 V
Phase3 Ph
Rated current150 A
Circuit breaker400 A
Dimensions (L×W×H)3993×1867×2206 mm
Dry weight3629 kg
Sound level69.0 dBA @ 23 m
Fuel tank977.0 L
Tank runtime24 hr

Engine

Power Solutions International 8.8L Industrial Powertrain
Oil capacity7.6 L
Coolant capacity13.7 L
Displacement8.8 L
AspirationTurbo Charge Air Cooled
Rated speed1800 rpm

Maintenance & consumables

for the Power Solutions International 8.8L Industrial Powertrain
ItemSpecCapacityPart #Interval
Air filterAir Cleaner AssyGM62308 Amazon eBay
Oil filter×1
CoolantClosed-Loop Radiator System49.2 L
Oil8.5 L

Service intervals

2
ItemActionHoursMonthsNotes
Paralleling boxInspect12 moAnnually by a Kohler authorized distributor/dealer, or when wear, damage, deterioration, or malfunction is evident or suspected.
Paralleling box internal componentsInspect1 moMonthly or when a condition noticed during external inspection may have affected internal components; enclosure cover must be removed by trained personnel.

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Service specifications

6
TypeItemValueUnitCondition
OtherEngine speed adjustment50default setting; settings between 40 and 60 acceptable; 52 increases speed by 2 RPM, 49 decreases by 1 RPM
OtherGenerator to bus phase angle-10 to 10degreesverify with contactor closed
OtherReactive droop1%default setting; range 0.5 - 2%
TorquePGEN terminal block connections0.5Nm
TorquePGEN terminal block connections4.4in. lbs.
VoltageController measurement accuracy2%without calibration; requires a calibrated multimeter for calibration

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Procedures

12
Calibration adjustment

⚠ Copying personality profiles from one controller to another can overwrite calibration coefficients and requires re-calibration.

Tools: Calibrated multimeter with recent calibration verification

  1. Use a calibrated multimeter to measure the generator voltage and enter the correct value in the CONTROLLER CONFIG -> CALIBRATION screen.
  2. Use a calibrated multimeter to measure the bus voltage and enter the correct value in the CONTROLLER CONFIG -> CALIBRATION screen.
Verify Generator Operation diagnostic

⚠ Generators must all operate at the same frequency, voltage, and phase connection in order to parallel.

Tools: SiteTech software

  1. Ensure the load is not connected or is drawing less power than a single generator can provide.
  2. Navigate to CONTROLLER CONFIG -> COMMUNICATION SETUP and verify PGEN Nodes Online indicates the correct number of nodes.
  3. Verify alternator connection (voltage selector switch position), system voltage, and voltage regulator target on each generator.
  4. Start a single generator by pressing the Run button; the paralleling box contactor should close and the Generator Connected to Bus indicator should light.
  5. Verify bus and generator voltages match and generator to bus phase angle is between -10 and 10 degrees.
  6. Verify the load bus is energized and available at the load.
  7. Stop the generator by pressing the OFF button; the contactor should open.
  8. Repeat for each generator in the paralleling system.
Verify Paralleling and Load Sharing diagnostic

Tools: Load bank (optional)

  1. Place all generators in automatic mode by pressing the Auto button; verify the red shutdown indicator is not illuminated.
  2. Provide a local start request by holding AUTO, pressing RUN, releasing RUN, then releasing AUTO.
  3. Verify all generators start, one generator closes its contactor, and the others synchronize and close their contactors.
  4. Verify that the % of rated power of the generators matches, showing the generators are sharing load equally.
  5. If a load bank is available, test the system under load.
Control Harness Connections installation

⚠ The control harness connections for GEN 1 and GEN 2 must correspond to the source camlock cable connections.

  1. Connect the control harness from the generator set connected to the GEN 1 camlock connectors to GEN 1 CONTROL.
  2. Connect the control harness from the generator set connected to the GEN 2 camlock connectors to GEN 2 CONTROL.
  3. When not used, store the control harnesses on the storage rack inside the enclosure.
Grounding installation

⚠ Grounding electrical equipment: hazardous voltage can cause severe injury or death. Turn off the main circuit breakers of all power sources before servicing.

  1. Connect the ground lug on the paralleling box to earth ground according to applicable state and local codes.
  2. Follow NEC guidelines for grounding electrical equipment.
  3. The neutral is bonded to ground inside the paralleling box; if required, remove the bonding bus to disconnect neutral from ground.
Load Connections installation

⚠ Multiple power sources can automatically energize the distribution bus. Disconnect all power sources before connecting to the distribution bus.

  1. Remove the camlock security guard from one row of connectors for each generator and store the guard.
  2. Connect the load side ground (green) camlock cables to the distribution bus and then to the paralleling box.
  3. Connect the load side neutral (white) camlock cables to the distribution bus and then to the paralleling box.
  4. Connect the load side L1 (black), L2 (red), and L3 (blue) camlock cables to the distribution bus and then to the paralleling box.
Multiple Paralleling Boxes (PGEN Connections) installation
  1. Connect one or two generators to each paralleling box.
  2. Use Belden cable #9841 (or equivalent) shielded twisted-pair communication cable to connect the PGEN terminal blocks on the paralleling boxes.
  3. Tighten the connections to 0.5 Nm (4.4 in. lbs.).
Paralleling System Setup installation

⚠ Generator management must be disabled manually at each generator set controller.

Tools: Personal computer with SiteTech software

  1. Check that the voltage selector switch and/or alternator wiring matches the building voltage configuration for all generator sets.
  2. Set the digital output to Contactor (SiteTech Programmable Digital Output 116).
  3. Set reactive droop to 0.5-2% (default 1%), using the same reactive droop setting on all generators.
  4. Set the target voltage on all paralleled generators to the same value.
  5. Set engine speed adjustment to 50 on all generators (default 50; range 40-60).
  6. Verify metering; if voltage is incorrect, use the calibration procedure.
  7. Set Sync Mode in AUTO to ACTIVE and Sync Mode in Run to CHECK on all generators.
  8. Set Generator Management Enabled to OFF at each generator unless generator management is requested.
  9. Set up load management (load shed priorities) for non-critical loads.
  10. Stop all generators by pressing the OFF button on each controller.
Source Connections installation

⚠ Hazardous voltage. This equipment must be installed and serviced by qualified electrical personnel. Do not connect or disconnect cables under load.

  1. Remove the camlock security guard from one row of connectors for each generator and store the guard.
  2. Generator 2 connects to the upper set of camlocks; generator 1 connects to the lower set.
  3. Connect the source side ground (green) camlock cables to the paralleling box first and then to each generator.
  4. Connect the source side neutral (white) camlock cables to the paralleling box first and then to each generator.
  5. Connect the source side L1 (black), L2 (red), and L3 (blue) camlock cables to the paralleling box first and then to each generator.
Storage Procedure maintenance

⚠ Do not open the electrical compartment on the opposite side of the enclosure; that compartment should be opened only by Kohler authorized distributors or dealers.

  1. Store control harnesses on the storage rack inside the box when not in use.
  2. Lock the cabinet door with the key provided and store the key in a secure location.
  3. Use the guards to cover the camlock connectors.
  4. Attach padlocks to the electrical panel cover and the camlock guards to prevent unauthorized access.
Disable the Generator Sets operation

⚠ Accidental starting can cause severe injury or death. Remove the negative (-) lead first when disconnecting the battery; reconnect it last.

  1. Press the generator set master control OFF/RESET button.
  2. Disconnect the power to the battery charger, if equipped.
  3. Disconnect the generator set engine starting battery(ies), negative (-) lead first.
Re-enable the Generator Sets operation

⚠ Reconnect the battery correctly, positive to positive and negative to negative, to avoid electrical shock and damage.

  1. Check that the generator set is OFF.
  2. Reconnect the generator set engine starting battery, negative (-) lead last.
  3. Reconnect power to the battery charger, if equipped.

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Common questions

What is the power rating of the Kohler 125REZGT?

The Kohler 125REZGT is rated 105 kW standby (131.0 kVA).

What engine does the Kohler 125REZGT use?

The Kohler 125REZGT is powered by the Power Solutions International 8.8L Industrial Powertrain engine.

What kind of fuel does the Kohler 125REZGT run on?

The Kohler 125REZGT runs on LP/NG.

What is the oil capacity of the Kohler 125REZGT?

The Power Solutions International 8.8L Industrial Powertrain engine in the Kohler 125REZGT has an oil capacity of 7.6 liters.

What air filter does the Kohler 125REZGT use?

The Kohler 125REZGT uses air filter part number GM62308.

Parts

16
Part #DescriptionQtySystem
125REZGTService Kit (Spares)Service kit Amazon eBay
273113Gasket–Intake1Air filter Amazon eBay
35/45REOZT4Service Kit (Spares)Service kit buy
DEC3500Generator set controller, all mobile, marine and stationary Tier 4 final generators, onboard paralleling: up to 8 gensets, protocols supported: Modbus® RTU1Controller Amazon eBay
GM19721Gasket, exhaust manifold2Gasket Amazon
GM62308Air Cleaner Assy1Air filter Amazon eBay
GM62309Element, air cleaner1Oil filter Amazon eBay $91.00
GM69285Hose, Air Intake1Hose Amazon eBay
GM87592Oil filter1Oil filter Amazon eBay $37.50
GM87608Spark plug8Oil filter Amazon eBay $60.00
GM91375Residential Service Truck KitService truck kit Amazon eBay
GM92062-SMaintenance KitMaintenance kit Amazon eBay
GM92063-SMaintenance KitMaintenance kit Amazon eBay
GM92098-SMaintenance KitMaintenance kit Amazon eBay
GM92099-SMaintenance KitMaintenance kit Amazon eBay
GM1018245.7L breather retrofit kit (not fully specified)1Service part / kit Amazon eBay

Service, wear & replacement parts referenced for this model and its engine — confirm the exact part for your serial number. See the full parts catalog to search and cross-reference.

Fuel consumption

RatingLoadL/hgal/h
Prime50%6.11.6
Prime75%8.82.3

Available documents

Spec sheet — Towable Mobile Generators Brochure (Kohler)Reference — Kohler-Gas Generators Brochure (Kohler)Reference — Mobile Rental Generators (Kohler)Owner's manual — tp6935 (Kohler)Parts manual — tp6846 (Kohler)Parts manual — tp6937 (Kohler)Service manual — tp6936 (Kohler)Service manual — tt1672 (Kohler)