Generator Service Intervals and Maintenance Plan

Two counters determine when a generator is due for service: running hours and the calendar. Whichever comes first, that is when the service is carried out. This simple rule is applied wrongly at many sites. On a standby set that runs 30 hours a year, the service is postponed because “500 hours have not been reached”; on a construction site set that runs continuously, the calendar is watched and the hour meter is overlooked. In this article we explain how to plan service intervals and what a service plan consists of. For the full list of daily, weekly and monthly checks, see our generator maintenance checklist.

The type of use determines the service plan

Two generators of the same model can have completely different service plans depending on how they are used:

Use	Annual running time	What sets the service interval	Main risk
Standby	Low; a limited number of hours a year	Calendar	Battery, stale fuel, low-load running
Continuous / prime power	High; regular, long running periods	Running hours	Oil and filter life, wear
Construction site and rental	Variable	Both hours and calendar	Dust, fuel contamination, transport knocks

The most common faults on standby sets come from not being used. On continuously running sets, keeping to the change intervals for oil and filters directly determines engine life.

Typical service intervals

The table below summarises intervals commonly applied to diesel generators. The binding reference is always the maintenance manual of the engine and alternator manufacturers; the table is a framework to start planning from.

Interval	Main tasks
Every run / weekly	Oil and coolant levels, leaks, battery charge indicator, alarm logs
Monthly	Test run on or off load, battery terminals, air filter indicator
250–500 hours or annually	Engine oil and oil filter, fuel filters, air filter check or replacement, belts
1,000 hours or every 2 years	Coolant analysis or replacement, thermostat and hose check, injector check (per manual)
Longer intervals	Valve clearance adjustment, turbocharger check, alternator insulation measurement, engine overhaul assessment

Dusty sites, high ambient temperatures and fuel of uncertain quality call for shorter intervals. For the air filter and fuel filter in particular, the decision to replace should be based on the indicator and inspection.

Why the calendar matters: what deteriorates on sets that rarely run?

On a set that does not run for long periods, time itself causes wear:

• Engine oil retains moisture from the air and combustion residues; it becomes acidic even if the hours have not been reached.
• Diesel fuel standing in the tank can form water and microbial sediment, which clogs the filters.
• Coolant additives lose their effect over time, and the risk of corrosion increases.
• The battery loses capacity even when unused; it is usually the weakest link in the system.

For this reason, at least one comprehensive service a year and regular test runs are recommended for standby sets. Carrying out the test run under real load where possible prevents the combustion residues caused by low-load running (wet stacking). If a real load cannot be applied, a load bank test is an option.

Elements of a good service plan

Knowing the service intervals is not enough; they have to be followed up. An effective service plan includes:

1. Set inventory: model, serial number, engine and alternator type and commissioning date of each set.
2. Service schedule: the next service date based on hours and calendar, whichever falls first.
3. Service record: work carried out, parts replaced, values measured and the hour meter reading. This record is needed for fault analysis and warranty processes.
4. Critical parts stock: frequently replaced parts such as filters, belts and batteries kept on site or nearby. For which parts to keep in stock, see our article on generator spare parts.
5. Test programme: who carries out the monthly test run, at what load and for how long.
6. Fault communication: who is to be called in the event of a fault and how long the service team takes to reach the site.

At sites with several sets, handing this plan over to a service company under a maintenance contract ensures that follow-up is handled from a single point.

Our service

Our own service teams work in Türkiye, in İstanbul, Kocaeli, Tekirdağ, Yalova, Ankara and Kırıkkale. Outside these provinces we work with contracted service partners in Türkiye. In the İstanbul and Ankara regions (Türkiye), we respond to breakdowns within 2–4 hours. With our mobile service vehicle we work on site, and we service and repair generators of all makes.

For generator sets installed outside Türkiye, maintenance should be carried out by a qualified local technician following the manufacturer’s manual. We supply filters and spare parts from Türkiye; see our spare parts supply page. You can send a maintenance or breakdown request through the service request form; stating the model of the set and the hour meter reading helps us prepare the right parts.

Summary

• Service is carried out at running hours or calendar, whichever comes first.
• The calendar is decisive for standby sets, running hours for continuously running sets.
• The intervals in the tables are a framework; the manufacturer’s maintenance manual is what counts.
• Maintenance that is not recorded is treated as maintenance that was not done.