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Kohler 2.5L Engine

The Kohler 2.5L is a 2.5 L engine. It powers generator sets from Kohler, including the 125REZGT and 45 REOZT4.

Also known as: KOHLER® 2.5L

2.5 L

Displacement

On this pageSpecs Generator sets FAQ Service intervals Torque & specs Fluids Fault codes Procedures Wiring

Engine specifications

Displacement	2.5 L

Generator sets powered by this engine

Kohler 125REZGT Kohler 45 REOZT4

How to read your Kohler engine serial & model number →

Common problems

Voltage reconnection
Fix: Affix a notice to the generator set after reconnecting the set to a voltage different from the voltage on the nameplate. Order voltage reconnection decal 246242 from an authorized service distributor/dealer.
Unbalanced weight
Fix: Do not use lifting eyes. Lift the generator set using lifting bars inserted through the lifting holes on the skid.
Servicing the exhaust system. Hot parts
Fix: Do not touch hot engine parts.
Parallel Operation
Fix: This product includes features intended to support operation in parallel with the utility grid, but these features have not been evaluated for compliance with specific utility interconnection protection standards or requirements.
Osed moving parts
Fix: Keep hands, feet, hair, clothing, and test leads away from the belts and pulleys when the generator set is running. Replace guards, screens, and covers before operating the generator set.
Hot engine and exhaust system
Fix: Do not work on the generator set until it cools.
Hot coolant and steam
Fix: Before removing the pressure cap, stop the generator set and allow it to cool. Then loosen the pressure cap to relieve pressure.
Canadian installations only
Fix: For standby service connect the output of the generator set to a suitably rated transfer switch in accordance with Canadian Electrical Code, Part 1.

Compiled from service & troubleshooting documentation across every generator set that uses the Kohler 2.5L.

Service intervals

Item	Action	Hours	Months	Notes
Filter(s)	Replace	150 hr	3 mo	Service more frequently if operated in dusty areas
Oil	Change	150 hr	3 mo	Every 150 Hours or 3 Months
Blow dust out of alternator	Clean	300 hr		2 Yrs or 300 Hrs; service more frequently in dusty areas
Valve clearance	Adjust	500 hr		3 Yrs or 500 Hrs
Wire-cable insulation breakdown	Test	500 hr		3 Yrs or 500 Hrs
Coolant	Change	1500 hr		1500 Hours
Alternator end bracket bearing	Replace	10000 hr		20--300 kW models; prime power applications
Coolant temperature protection level	Check		6 mo	Six Months
Paralleling box	Inspect		12 mo	Annually by a Kohler authorized distributor/dealer, or when wear, damage, deterioration, or malfunction is evident or suspected.
Paralleling box internal components	Inspect		1 mo	Monthly or when a condition noticed during external inspection may have affected internal components; enclosure cover must be removed by trained personnel.
Safety and alarm operation	Check		6 mo	Six Months
Safety and alarm operation	Test		6 mo	Six Months
Tighten DC electrical connections	Check		6 mo	Six Months
Wheel lug nut torque	Check			First service — First 80/160 km (50/100 miles); then Quarterly or 3000 Miles

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

Type	Item	Value	Unit	Condition
Other	Alternator protection current/time limits	200%: 40 seconds; 300%: 10 seconds; 425%: 5 seconds; 950%: 1 second		rated current percentage
Other	Battery specific gravity (charge threshold)	1.215	specific gravity	at 26.7 C (80 F); charge if below
Other	Battery specific gravity (fully charged)	1.260	specific gravity	at 26.7 C (80 F) electrolyte temperature
Other	Controller operating temperature range	--40 to 70 C (--40 to 158 F)
Other	Controller power drain	400 milliamps at 12V; 200 milliamps at 24V
Other	Engine speed adjustment	50		default setting; settings between 40 and 60 acceptable; 52 increases speed by 2 RPM, 49 decreases by 1 RPM
Other	Gaseous fuel tank maximum safe fill level	80	% of total fuel tank volume
Other	Generator to bus phase angle	-10 to 10	degrees	verify with contactor closed
Other	LP gas fuel system leak test pressure	6--8 ounces per square inch (10--14 inches water column)	oz/in2 (in. water column)	test pressurized
Other	Reactive droop	1	%	default setting; range 0.5 - 2%
Other	Wheel stud size	1/2-20
Pressure	Fuel tank pressure relief valve (close)	1937--2130	kPa (281--309 psi)
Pressure	Fuel tank pressure relief valve (open)	2151	kPa (312 psi) min
Pressure	Tire inflation pressure @ rated load	552 (80 psi)	kPa (psi)
Speed	Overfrequency default setting	110% of nominal	%
Speed	Overfrequency setting range	102%--140% of nominal	%
Speed	Overfrequency time delay	10	sec
Speed	Underfrequency default setting	90% of nominal	%
Speed	Underfrequency setting range	80%--95% of nominal	%
Speed	Underfrequency time delay	10 (short term), 60 (long term)	sec
Torque	PGEN terminal block connections	0.5	Nm
Torque	PGEN terminal block connections	4.4	in. lbs.
Torque	Wheel lug nut torque	122 (90)	Nm (ft. lb.)
Voltage	Controller measurement accuracy	2	%	without calibration; requires a calibrated multimeter for calibration
Voltage	High battery voltage default setting	15	V	12-volt engine electrical system
Voltage	High battery voltage default setting	30	V	24-volt engine electrical system
Voltage	High battery voltage range	13.2--16.2	V	12-volt engine electrical system
Voltage	High battery voltage range	26.4--32.4	V	24-volt engine electrical system
Voltage	Low battery voltage default setting	12	V	12-volt engine electrical system
Voltage	Low battery voltage default setting	24	V	24-volt engine electrical system
Voltage	Low battery voltage range	19.2--25.2	V	24-volt engine electrical system
Voltage	Low battery voltage range	9.6--12.6	V	12-volt engine electrical system
Voltage	Overvoltage default setting	120% at 2 sec	%
Voltage	Overvoltage setting range	105%--135% of nominal	%
Voltage	Overvoltage time delay range	2--10	sec
Voltage	Undervoltage default setting	80% of nominal at 10 sec	%
Voltage	Undervoltage setting range	70%--95% of nominal	%
Voltage	Undervoltage time delay range	5--30	sec

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

Recommended fluids

Fluid	Grade	Notes
Grease	Lithium complex	Axle bearing grease type
Grease	Multipurpose grease	Lubricate trailer hitch/coupler contact points
Grease	Petroleum jelly, silicon grease, or other nonconductive grease	Coat battery terminals after reconnecting
Grease	White lithium grease	Apply a small amount behind the brake shoe where it rubs against the backing plate

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

Fault codes

Code	Name	Severity
AC Sensing Lost		Warning
Alternator Protection		Shutdown
Auxiliary Input		Warning
Avg Current	High	Warning
Avg Gen Voltage L-L	Low	Warning
Battery Charger Fault		Warning
Cabinet Intrusion Alarm		Warning
Coolant Pressure	Low	Warning
Cranking Voltage	Low	Warning
ECM Communication Loss		Shutdown
ECM Model Mismatch		Shutdown
Electrical Metering Communication Loss		Shutdown
Emergency Stop		Shutdown
Engine Coolant Level	Low	Shutdown
Engine Coolant Temperature	Low	Warning
Engine Derate Active		Warning
Engine Fuel Level	Low	Warning
Engine Oil Level	Low	Warning
Engine Oil Pressure	Shorted High	Warning
Failure To Synchronize		Warning
Fuel Pressure	Low	Warning
Fuel Tank Leak		Warning
Fuel Temperature	High	Warning
Gen Battery Voltage	Low	Warning
Generator Frequency	Low	Warning
Generator Voltage L1-L2	Low	Shutdown
Ground Fault Input		Warning
Injector Wiring Fault		Warning
Intake Air Temperature	High	Warning
Locked Rotor		Shutdown
Maximum Alternator Current	Low	Shutdown
Not In Auto		Warning
Over Crank		Shutdown
Reserve Oil Empty		Warning
Run Relay Coil Overload		Shutdown
Speed Sensor Fault		Warning
Starter Relay Coil Overload		Shutdown
System Frequency	High	Warning
System Voltage	High	Warning
Total Power (Generator Total Real Power)	Low	Warning
Total Reactive Power	Low	Warning
Water In Fuel		Warning

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

Procedures

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

Use a calibrated multimeter to measure the generator voltage and enter the correct value in the CONTROLLER CONFIG -> CALIBRATION screen.
Use a calibrated multimeter to measure the bus voltage and enter the correct value in the CONTROLLER CONFIG -> CALIBRATION screen.

Electric Brake Adjustment adjustment

⚠ Never use compressed air to clean brake components; some components may contain asbestos.

Tools: Adjustment tool or large slotted screwdriver, Jack stands

Raise the trailer with wheels off the ground and block safely with jack stands; remove the wheel.
Remove the rubber plug from the backing plate slot.
Insert an adjustment tool or large slotted screwdriver in the slot and rotate the star wheel to expand the shoe against the drum.
Expand the shoe until the drum can't be turned by hand to center each shoe.
Back off the adjustment in the other direction until the drum turns freely with slight resistance.
Replace the rubber plug in the backing plate slot.
Repeat procedure for remaining wheels.

Verify Generator Operation diagnostic

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

Tools: SiteTech software

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

Verify Paralleling and Load Sharing diagnostic

Tools: Load bank (optional)

Place all generators in automatic mode by pressing the Auto button; verify the red shutdown indicator is not illuminated.
Provide a local start request by holding AUTO, pressing RUN, releasing RUN, then releasing AUTO.
Verify all generators start, one generator closes its contactor, and the others synchronize and close their contactors.
Verify that the % of rated power of the generators matches, showing the generators are sharing load equally.
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.

Connect the control harness from the generator set connected to the GEN 1 camlock connectors to GEN 1 CONTROL.
Connect the control harness from the generator set connected to the GEN 2 camlock connectors to GEN 2 CONTROL.
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.

Connect the ground lug on the paralleling box to earth ground according to applicable state and local codes.
Follow NEC guidelines for grounding electrical equipment.
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.

Remove the camlock security guard from one row of connectors for each generator and store the guard.
Connect the load side ground (green) camlock cables to the distribution bus and then to the paralleling box.
Connect the load side neutral (white) camlock cables to the distribution bus and then to the paralleling box.
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

Connect one or two generators to each paralleling box.
Use Belden cable #9841 (or equivalent) shielded twisted-pair communication cable to connect the PGEN terminal blocks on the paralleling boxes.
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

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

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

Voltage Reconnection Procedure (with Selector Switch) installation

⚠ Do not move the voltage selector switch while the generator set is running.

⚠ Affix voltage reconnection decal 246242 after reconnecting to a different voltage.

Tools: User-supplied load lug wrench

Press the generator set master control OFF/RESET button.
Open the main line circuit breaker.
Navigate to Generator Info then Voltage Selector Switch menu; press the selector dial.
Select Present Position and change to the desired selection (Three Phase Wye 480 V, Three Phase Wye 208 V, or Single Phase Dogleg).
Rotate the voltage selector switch on the junction box to match the desired voltage shown on the controller.
Disconnect the engine starting battery, negative lead first; disconnect battery charger power.
Make lead connections between load devices and the load lugs or camlocks.
Make a ground connection to earth ground per NEC guidelines.
Replace all electrical guards, barriers, and covers.
Reconnect the battery, negative lead last; reconnect battery charger power.
Press RUN to start and check voltages on the display.
Press OFF/RESET to stop.
Close the main line circuit breaker and any downstream circuit breakers.

Voltage Reconnection Procedure (without Selector Switch) installation

⚠ Hazardous voltage. Disconnect all power sources before opening the enclosure.

Tools: User-supplied load lug wrench

Press the generator set master control OFF/RESET button.
Open the main line circuit breaker.
Navigate to Generator Info, then Configuration, then Generator Config menu.
Set System Voltage L--L to the desired voltage (208 V, 240 V, or 480 V).
Set System Phase to Three Phase or Single Phase.
Verify settings match the desired voltage/frequency/phase.
Disconnect the engine starting battery, negative lead first; disconnect battery charger power.
Use the reconnection diagram to route leads through current transformers and reconnect.
Make load connections and a ground connection per NEC guidelines.
Replace all electrical guards, barriers, and covers.
Reconnect the battery, negative lead last; reconnect battery charger power.
Press RUN to start and check voltages.
Press OFF/RESET to stop.
Close the main line circuit breaker and any downstream circuit breakers.

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

Voltage	Phase	Connection	Leads	Notes
	1	Camlocks (left to right)	Green=GND; White=L0; Black=L1; Red=L2	Single-phase uses four camlocks
	3	Camlocks (left to right)	Green=GND; White=L0; Black=L1; Red=L2; Blue=L3	Three-phase uses all five camlocks
120/208	3	Low wye	L0-L1: 120; L1-L2: 208; L1-L3: 208; L2-L3: 208	Voltage selector switch position Low wye; selector switch factory set Pos. 2 Volts 120/208, 60 Hz, Three Phase Wye
120/240	1	Single-phase	L0-L1: 120; L1-L2: 240	Voltage selector switch position Single-phase; selector switch factory set Pos. 3 Volts 120/240, 60 Hz, Single Phase Dogleg (3-position switch only)
277/480	3	High wye	L0-L1: 277; L1-L2: 480; L1-L3: 480; L2-L3: 480	Voltage selector switch position High wye; selector switch factory set Pos. 1 Volts 277/480, 60 Hz, Three Phase Wye

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 displacement of the Kohler 2.5L?

The Kohler 2.5L has a displacement of 2.5 liters.

Which generators use the Kohler 2.5L engine?

The Kohler 2.5L powers 2 generator set(s), including Kohler 125REZGT, Kohler 45 REOZT4.

What is a common problem with the Kohler 2.5L engine?

A commonly reported issue on generators using the Kohler 2.5L is: Voltage reconnection. Fix: Affix a notice to the generator set after reconnecting the set to a voltage different from the voltage on the nameplate. Order voltage reconnection decal 246242 from an authorized service distributor/dealer..