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Kohler 30REZG Generator Set

The Kohler 30REZG is a 30 kW (38 kVA) Natural Gas / LP standby generator set powered by a General Motors 3.0L engine. It is available at 480 V, 3-phase and 60 Hz. It holds about 4.7 L (1.2 gal) of oil and 14.9 L (3.9 gal) of coolant, with a maximum ambient rating of 50 °C. The set produces 74 dBA at 23 m. The same 3.0L engine also powers generator sets from Genie.

30 kW
Standby
3.0 L
Displacement
4.7 L
Oil capacity
5
Document types

How to read your Kohler serial & model number →

Typical fuel consumption for 30–35 kW Bi-Fuel (NG/LP) generators →

Compare with other 30–35 kW Bi-Fuel (NG/LP) generators →

Service parts for the 30REZG

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

Air intake

1 required

Oil system

1 required

Belts

1 required

Ignition

1 required

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

Specifications

FuelNatural Gas / LP
Frequency60.0 Hz
Standby power30 kW
Standby kVA38
Prime power27 kW
ControllerDecision-Maker 3000, Decision-Maker 3500
Oil capacity4.7 L
AlternatorPMG
Voltage options480 V
Phase3
Max ambient50 °C
Sound level74.0 dBA @ 23 m

Engine

General Motors 3.0L
Oil capacity4.7 L
Coolant capacity14.9 L
Displacement3.0 L
AspirationNatural Aspiration
Rated speed1 rpm

Maintenance & consumables

for the General Motors 3.0L
ItemSpecCapacityPart #Interval
Air filterElement, air cleaner253107 Amazon $43.25 eBay $69.00
Fuel filter
Oil filterGM16703 Amazon $9.06 eBay $58.00
Battery
BeltBelt, alternatorGM39428 Amazon eBay $15.00
Coolant
Oil
Spark plugSpark plugGM38998 Amazon eBay

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

36
TypeItemValueUnitCondition
Other10 in. weld flange bolt circle diameter B361.95mm (14.25 in.)
Other10 in. weld flange outside diameter C406.4mm (16.0 in.)
Other10 in. weld flange quantity of bolts / bolt hole diameter D12, 25.40mm (1.00 in.)
Other12 in. weld flange bolt circle diameter B431.80mm (17.00 in.)
Other12 in. weld flange outside diameter C482.6mm (19.0 in.)
Other12 in. weld flange quantity of bolts / bolt hole diameter D12, 25.40mm (1.00 in.)
Other14 in. weld flange bolt circle diameter B476.25mm (18.75 in.)
Other14 in. weld flange outside diameter C533.4mm (21.0 in.)
Other14 in. weld flange quantity of bolts / bolt hole diameter D12, 28.58mm (1.13 in.)
Other16 in. weld flange bolt circle diameter B539.75mm (21.25 in.)
Other16 in. weld flange outside diameter C596.9mm (23.5 in.)
Other16 in. weld flange quantity of bolts / bolt hole diameter D16, 28.58mm (1.13 in.)
Other18 in. weld flange bolt circle diameter B577.85mm (22.75 in.)
Other18 in. weld flange outside diameter C635.0mm (25.0 in.)
Other18 in. weld flange quantity of bolts / bolt hole diameter D16, 31.75mm (1.25 in.)
Other20 in. weld flange bolt circle diameter B635.00mm (25.00 in.)
Other20 in. weld flange outside diameter C698.5mm (27.5 in.)
Other20 in. weld flange quantity of bolts / bolt hole diameter D20, 31.75mm (1.25 in.)
Other5 in. weld flange bolt circle diameter B215.90mm (8.50 in.)
Other5 in. weld flange outside diameter C241.30mm (9.50 in.)
Other5 in. weld flange quantity of bolts / bolt hole diameter D8, 22.23mm (0.88 in.)
Other6 in. weld flange bolt circle diameter B254.0mm (10.0 in.)
Other6 in. weld flange outside diameter C279.4mm (11.0 in.)
Other6 in. weld flange quantity of bolts / bolt hole diameter D8, 22.23mm (0.88 in.)
Other8 in. weld flange bolt circle diameter B298.45mm (11.75 in.)
Other8 in. weld flange outside diameter C342.9mm (13.5 in.)
Other8 in. weld flange quantity of bolts / bolt hole diameter D8, 22.23mm (0.88 in.)
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%
OtherWeld flange angle A (10, 12, 14 in. nominal pipe size)30deg.
OtherWeld flange angle A (16, 18, 20 in. nominal pipe size)22.5deg.
OtherWeld flange angle A (5, 6, 8 in. nominal pipe size)45deg.
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.

Voltage reconnection

VoltagePhaseConnectionLeadsNotes
12-LeadAlternator Reconnections diagram ADV-5875B-M (page 16)
4-LeadAlternator Reconnections diagram ADV-5875A-M (page 15)

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 30REZG?

The Kohler 30REZG is rated 30 kW standby (38.0 kVA).

What engine is in the Kohler 30REZG?

The Kohler 30REZG is powered by the General Motors 3.0L engine.

What fuel does the Kohler 30REZG use?

The Kohler 30REZG runs on Natural Gas / LP.

How much oil does the Kohler 30REZG take?

The General Motors 3.0L engine in the Kohler 30REZG has an oil capacity of 4.7 liters.

What alternator comes on the Kohler 30REZG?

The Kohler 30REZG uses a PMG alternator.

Which oil filter part number does the Kohler 30REZG take?

The Kohler 30REZG uses oil filter part number GM16703.

Which air filter part number does the Kohler 30REZG take?

The Kohler 30REZG uses air filter part number 253107.

Troubleshooting

2

Symptoms & remedies

SymptomCauseRemedy
Low Coolant Temperature (LCT) fault alarms occur even when a block heater is installed and properly functioning.The LCT sender was installed in the incorrect location on the unit. In this case, the sender was installed in a tee fitting on the return line from the engine block to the block heater. The correct LCT location is in the thermostat housing.
The LCT sender/switch at the tee of the return line between the engine block and block heater has two terminals, indicating it is an incorrect sender/switch.Order LCT sender GM39458. Go to step 1.3.

Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.

Parts

18
Part #DescriptionQtySystem
1259369GTManifoldsManifold Amazon eBay
253107Element, Air Cleaner1Air filter Amazon $43.25 eBay $69.00
4024TF281Fan Belt1Belt Amazon eBay
GM16132Belt, fan standard1Belt Amazon eBay $86.00
GM16531Spark plug1Oil filter Amazon eBay $8.08
GM16703Filter, oil1Oil filter Amazon $9.06 eBay $58.00
GM19726Thermostat1Spark plug Amazon eBay
GM22171Spark plug8Oil filter Amazon eBay
GM34935Fuel Filter1Fuel filter Amazon eBay $37.99
GM38998Spark plug1Oil filter Amazon eBay
GM39428Belt, alternator1Oil filter Amazon eBay $15.00
GM39458LCT Sender1Sensor Amazon eBay
GM62309Element, air cleaner1Oil filter Amazon eBay $91.00
GM63750Oil Filter1Oil filter Amazon eBay
GM63809Fuel Filter (primary)1Fuel filter Amazon eBay
GM65427Belt, alternator1Oil filter Amazon eBay $79.00
GM74021-CPipe sealantFluid Amazon eBay
GM79585--SThermostat1Thermostat Amazon eBay 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
Prime25%138.036.46
Prime50%192.050.72
Prime75%251.066.31
Prime100%314.082.95
Prime110%345.091.14
Standby25%144.038.04
Standby50%204.053.89
Standby75%271.071.59
Standby100%345.091.14

Available documents

Spec sheet (Kohler)Spec sheet — Towable Mobile Generators Brochure (Kohler)Reference (Kohler)Reference — G6-39 0918AZ (Kohler)Reference — Reinstated Enclosures (Kohler)Owner's manual — tp6935 (Kohler)Parts manual — tp6801 (Kohler)Parts manual — tp6937 (Kohler)Service manual — sb710 (Kohler)Service manual — tp6712 (Kohler)Service manual — tp6799 (Kohler)Service manual — tp6936 (Kohler)Service manual — tt1672 (Kohler)
A real unit
Kohler 30REZG generator

Photo of a real Kohler 30REZG — from a surplusrecord.com listing, 2026.

Real-unit nameplate
Kohler 30REZG generator nameplate / data tag

Nameplate from a real Kohler 30REZG — from a surplusrecord.com listing, 2026. How to read one →

Full service, cheapest listings

Priced items from this model's own parts manual.

Air filter 253107$43.25
Oil filter GM16703$9.06
Belt GM39428$15.00
3 priced items$67.31