Generator Maintenance Checklist

Generator maintenance consists of daily and weekly visual checks, a monthly test run under load, oil and filter changes at set running hours, and a comprehensive annual service. Because backup generators run little, maintenance must be planned by both running hours and calendar. The list below is a general framework; for exact intervals and materials, the engine and alternator manufacturers’ maintenance manuals should be followed.

Why scheduled maintenance?

A backup generator is only valuable if it runs when needed. The common reasons generators fail to start during an outage are simple: a flat battery, fuel problems, low coolant, loose connections. Most of these can be caught in advance with regular checks.

Daily checks (for continuously running sets)

On sets running at prime power, on construction sites or as the primary source, before each start:

• Engine oil level
• Coolant level (with the engine cold)
• Fuel level and visible leaks
• Alarm and warning logs on the control panel
• Air filter restriction indicator (if fitted)

Weekly checks

• General visual check for oil, fuel and coolant leaks
• Check that the battery charger is working and battery voltage is normal
• Check that the block heater (jacket water heater) is working
• Confirm that the control panel is in automatic mode
• Clean inside the canopy and keep air inlets and outlets clear

Monthly checks

• Test run under load: Run the set not at no load but, where possible, under the real load or a meaningful load. Testing together with the transfer (ATS) panel shows that the system works end to end.
• Cleanliness and tightness of battery terminals; battery electrolyte level (on types that require maintenance)
• Belt tension and wear
• Cleanliness of the radiator fins and condition of the hoses
• Check the fuel tank for water and sediment, drain the water separator
• Check the exhaust system for leaks and connections

250–500 hour interval or annual service

On many industrial diesel engines, oil and filter changes are specified within this interval; however, the exact value varies with the engine model, oil type and operating conditions. On sets that run little, the calendar applies even if the hours have not been reached, and maintenance is usually carried out at least once a year.

• Engine oil and oil filter change
• Fuel filter and pre-filter (water separator) change
• Air filter check or replacement
• Check of the coolant’s antifreeze and additive concentration
• Check of belts, hoses and clamps
• Test of engine protection sensors and alarms
• Check of alternator connections, cable terminations and earthing

Annual and long-interval checks

• Load bank test: Running the set for a set period at a load close to its rated power; this verifies the engine, alternator and cooling system at real capacity.
• Battery capacity test and replacement according to age
• Coolant renewal according to the manufacturer’s recommendation
• Alternator winding insulation resistance measurement
• Verification of control and protection settings and ATS transfer times
• Fuel tank cleaning and fuel quality analysis
• Check of anti-vibration mounts, base frame and canopy fixings

Battery: the most common point of failure

A significant proportion of start failures in standby generators are caused by the battery. Keeping the charger running continuously, keeping the terminals clean and tight and replacing the battery according to its age directly affect starting reliability.

Wet stacking and low-load operation

When a diesel engine runs at very low load for a long time, the cylinders do not warm up sufficiently; unburnt fuel and soot build up in the exhaust system. This is called wet stacking. The symptoms are black, oily discharge from the exhaust, loss of power and increased oil consumption.

To prevent it:

• Carry out test runs under a meaningful load, not at no load. Many manufacturers recommend a load of at least approximately 30% of rated power for regular runs; the exact recommendation comes from the engine manufacturer.
• Carry out a load bank test annually or when necessary.
• Avoid sizing the generator well above the requirement.

Safety during maintenance

• Before starting maintenance, put the control panel in the off/manual position and prevent automatic starting; remember that on systems with an ATS the set can start by itself during maintenance.
• When disconnecting the battery, remove the negative terminal first.
• Do not open the radiator cap while the engine is hot; pressurised hot coolant can cause burns.
• Take care around hot surfaces such as the exhaust and turbocharger; dispose of waste oil and filters in accordance with regulations.

The importance of record keeping

At every service, the running hours, work carried out, parts replaced and measured values should be recorded. These records allow faults to be detected early and are also important for warranty conditions.

Next step

Terex Diesel provides service and scheduled maintenance for the sets it sells. See our scheduled maintenance page for maintenance scope and planning; for a fault or maintenance request, contact us. To verify transfer behaviour during on-load tests, you can also see the ATS transfer panel page.