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Home›Engines›Cummins/Onan QSB5-G1 NR3

Cummins/Onan QSB5-G1 NR3 Engine

The Cummins/Onan QSB5-G1 NR3 is a 4.5 L turbocharged and charge air cooled engine rated at 1800 rpm. It powers generator sets from Terex, including the T70C. It holds 9 L (2.4 gal) of coolant.

Also known as: Cummins QSB5-G1 NR3

4.5 L
Displacement
1800 rpm
Rated speed
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Engine specifications

Coolant capacity9.0 L
Displacement4.5 L
Aspirationturbocharged and charge air cooled
Rated speed1800 rpm

Common problems

14
  • Voltage does not come up to the rated voltage
    Cause: Internal problem with the generator end
    Fix: Check for even reading across the lines, if they are not this would mean you probably have a problem with the wiring of the switch or generator. If the generator voltage reads correctly, contact the TEREX service department.
  • Uneven reading between the legs when applying 24 volts to the field wires
    Fix: Recheck your wiring connections. After you have the field wire connected start the unit again and check your output voltage. It may still be necessary to flash the fields to restore residual voltage.
  • TROUBLE LIGHT on CONTROL PANEL is illuminated
    Cause: Broken fan belt
    Fix: Inspect fan belt and replace as needed
  • No generator output voltage
    Cause: Circuit breaker tripped
    Fix: Reset circuit breaker
  • Malfunction discovered
    Fix: Identify symptoms, troubleshoot, perform repair, return to service
  • Low generator output voltage
    Cause: Voltage adjustment set too low
    Fix: Adjust voltage potentiometer
  • Low engine speed
    Fix: Call TEREX Service
  • High generator output voltage
    Cause: Voltage adjustment potentiometer set too high
    Fix: Adjust potentiometer
  • High engine speed
    Fix: Call TEREX Service
  • Fluctuating or surging generator output voltage
    Fix: Check engine fuel, oil, and air filters
  • Fluctuating generator output voltage stability
    Cause: Load may be the cause
    Fix: Redistribute load if possible
  • Engine won't crank
    Cause: Loose battery cable
    Fix: Check cables and battery electrolyte level. Recharge as necessary
  • Engine shuts down
    Cause: Oil Pressure Switch not opening automatically and TROUBLE LIGHT on
    Fix: Improper coolant use a 50/50 on
  • Engine runs, but loses power under load
    Cause: Clogged fuel system
    Fix: Check fuel system

Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan QSB5-G1 NR3.

Maintenance schedule

ItemSpecCapacityPart #Interval
Air filterClean/replace engine air cleaner element—250 hr
Oil filterChange engine oil and filter—1500 hr

Pooled from every document that names this exact engine — confirm the interval and part number against your unit's serial number.

Common questions

What is the displacement of the Cummins/Onan QSB5-G1 NR3?

The Cummins/Onan QSB5-G1 NR3 has a displacement of 4.5 liters.

Which generators use the Cummins/Onan QSB5-G1 NR3 engine?

The Cummins/Onan QSB5-G1 NR3 powers 1 generator set(s), including Terex T70C.

What is a common problem with the Cummins/Onan QSB5-G1 NR3 engine?

A commonly reported issue on generators using the Cummins/Onan QSB5-G1 NR3 is: Voltage does not come up to the rated voltage. Cause: Internal problem with the generator end. Fix: Check for even reading across the lines, if they are not this would mean you probably have a problem with the wiring of the switch or generator. If the generator voltage reads correctly, contact the TEREX service department..