A generator that fails during a power outage or on a remote site is worse than no generator at all. Regular inspections catch the issues that cause failures, from flat batteries and contaminated fuel to coolant leaks and worn belts, before they leave you without power when it matters most.
This guide is for site supervisors, maintenance technicians and plant operators responsible for diesel generators from 10 kVA portables through to 2,000 kVA standby installations. It covers the full inspection sequence, common faults, the difference between daily checks and scheduled services, and how to digitise the process.
Before you start
Prepare your generator inspection checklist, the unit's service manual and the run-hour reading. You will need a torch, hearing protection, safety glasses, nitrile gloves and a multimeter. Review the generator's asset record so you know when it was last serviced and any outstanding defects. For standby units on automatic transfer switches, set the unit to manual mode before beginning hands-on inspection.
Step-by-step inspection
1. Check fuel level and fuel system
Verify the fuel tank level is adequate for the planned run time. Inspect fuel lines, fittings and filters for leaks or cracks. Drain the water separator bowl. Check the shut-off valve operates freely and look underneath for fuel pooling. Diesel stored for long periods degrades, so check for discolouration or a sour smell.
2. Inspect engine oil and coolant
With the engine off and cool, check the dipstick sits between the min and max marks. Black or gritty oil is due for a change, and milky oil in particular can point to coolant contamination from a failing head gasket or oil cooler. Check coolant in the overflow bottle and radiator (only when cold), and inspect hoses, clamps and the water pump for leaks.
3. Check battery and electrical connections
Inspect battery terminals for corrosion or loose connections. Measure open-circuit voltage: 12.6 V is fully charged, 12.4 V is the minimum acceptable. Confirm the charger is maintaining float voltage. If fitted, check the block heater is warm to the touch.
4. Inspect the alternator and output panel
Check the alternator for loose wiring, damaged insulation or overheating. Review the control panel for warning lights, tripped breakers or stored fault codes. Confirm all gauges read within normal ranges.
5. Test start and run under load
Start the generator and let it reach operating temperature. Listen for abnormal knocking or misfiring. Black exhaust indicates over-fuelling, blue points to oil burning, white may signal a coolant leak. Apply load and verify voltage and frequency are stable (nominally 230 V and 50 Hz in Australia).
6. Record the inspection
Document findings, meter readings and defects in your inspection form. Record run hours, fuel level, oil condition and battery voltage. Flag overdue services and schedule maintenance tasks. Attach timestamped photos to support the written record.
Common faults
| Finding | Action |
|---|---|
| Battery flat or will not hold charge | Load-test the battery; replace if it fails to hold 12.4 V under load |
| Fuel contamination (water, microbial growth) | Drain and flush tank, replace filters, refuel with clean diesel |
| Coolant leak (hose, clamp, radiator or pump) | Do not run; identify source, repair and pressure-test |
| Oil low or discoloured/contaminated | Change oil and filter; investigate if consumption is excessive |
| Control panel fault code or warning light | Record code, consult OEM manual, clear only after root cause resolved |
| Excessive exhaust smoke | Black: check air filter/injectors. Blue: oil and rings. White: coolant/head gasket |
| Output voltage or frequency unstable under load | Check the AVR (automatic voltage regulator), governor and wiring connections |
Daily vs scheduled inspections
| Aspect | Daily / pre-use | Weekly (standby) | 250 hrs | 500 hrs | 1,000 hrs |
|---|---|---|---|---|---|
| Scope | Walk-around, fluid levels, leaks | Start and run under load 30 min | Oil/filter change, air filter | Fuel filter, belts, coolant test | Valves, injectors, coolant flush |
| Who | Operator | Operator or technician | Technician | Technician | Diesel mechanic |
| Duration | 5 to 10 min | 45 min | 1 to 2 hrs | 2 to 3 hrs | 4 to 8 hrs |
| Record | Daily checklist | Weekly run log | Service record | Service record + fluid analysis | Full service report |
| Template | Inspection checklist | Weekly run log | Maintenance checklist | 500-hr service sheet | Annual service sheet |
Service intervals
Always follow the OEM service schedule for your specific model. The intervals above are typical for diesel generators and serve as a general guide only.
In Australia, AS/NZS 3010 sets the requirements for the electrical installation of generating sets, including changeover switching, earthing and neutral management. Where a generator backs up fire safety or emergency systems, its testing also forms part of the routine maintenance regime for those systems, so confirm what your building or site classification requires. Whatever the classification, keep documented evidence of every test and service. Operators working to US rules will know the standby-generator testing regime as NFPA 110.
