What is included in a generator 500-hour service?

A 500-hour generator service is an intermediate service that includes all 250-hour tasks plus replacing the fuel filter element, replacing the outer air filter element, testing coolant concentration with a refractometer, replacing or retensioning the fan belt, checking alternator brushes and slip rings, inspecting the voltage regulator, testing the automatic transfer switch (ATS) operation, load testing the battery under CCA, cleaning and inspecting air intake and exhaust louvres, inspecting wiring and connections for heat damage, checking the fuel tank for water and sediment, testing all protection relays (over-current, under-voltage, over-speed), and taking an engine oil sample for analysis. It takes approximately 2 to 3 hours.

Why is oil sampling important for generators?

Oil sampling detects engine wear, contamination and oil degradation before they cause failures. A laboratory analysis of the oil sample can identify metal particles (indicating bearing or piston wear), coolant contamination (indicating a head gasket issue), fuel dilution, soot levels and oil condition. Trending results over multiple samples gives early warning of developing problems. This is particularly important for standby generators that may not run regularly but must perform reliably when needed.

How often should a generator ATS be tested?

The automatic transfer switch (ATS) should be tested at every 500-hour service interval. ATS testing verifies that the switch correctly detects a mains power failure, sends a start signal to the generator, transfers the load once the generator reaches stable voltage and frequency, and retransfers to mains when power is restored. A faulty ATS can mean the generator fails to start during a real outage, defeating the purpose of having standby power.

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Yes. Download and use the generator 500-hour service procedure for free. Open the file and use your browser's Print, then Save as PDF. No MapTrack account required. If you later want digital service procedures linked to each generator with scheduling by hours, cost tracking and alerts, we would be happy to show you MapTrack.

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Free generator 500-hour service checklist

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A step-by-step 500-hour (intermediate) service procedure for diesel generators. Includes all 250-hour tasks plus fuel filter and outer air filter replacement, coolant concentration testing, fan belt replacement, alternator and voltage regulator checks, ATS testing, battery load testing, protection relay testing, wiring inspection and engine oil sampling. Includes fluid specifications, parts list and technician sign-off. This page explains what the service involves, how to perform it, and offers a free PDF-ready form you can download straight away.

Last updated: 2026-03-26 · MapTrack

Jarrod Milford

Commercial Director

Updated 26 March 2026

How to use: Complete the 250-hour service first, then work through these additional 500-hour tasks. Tick Done as each task is completed. Record fluid quantities and part numbers used. Set the next service due hours and sign off.

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What is a generator 500-hour service?

A 500-hour service is the second tier of scheduled preventive maintenance for a diesel generator. It is performed every 500 engine hours and is classified as an intermediate service. It includes all tasks from the 250-hour service plus additional fuel system, air intake, cooling, alternator, electrical protection and oil analysis tasks. The 500-hour service adds fuel filter and outer air filter replacement, coolant concentration testing, fan belt replacement, alternator brush and voltage regulator inspection, ATS testing, battery load testing, wiring inspection, protection relay testing and engine oil sampling. It is typically performed by a qualified generator technician or electrician.

Benefits of scheduled generator servicing

Reliable power when needed: fuel filter and air filter replacement ensures clean fuel and air supply, preventing starting failures and power loss under load.
Early fault detection: oil sampling, protection relay testing and wiring inspection identify developing problems before they cause unplanned outages.
ATS confidence: testing the automatic transfer switch verifies the generator will start and take load automatically during a real power outage.
Extended component life: fan belt replacement, alternator brush checks and coolant concentration testing prevent premature wear on critical components.
Compliance: documented service records demonstrate that generators are maintained to Australian Standards and WHS requirements.
Lower total cost: regular intermediate servicing is far cheaper than emergency callouts or major rebuilds caused by deferred maintenance.

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Service actions included in the 500-hour procedure

This service procedure covers 13 additional service actions across 7 system areas (in addition to all 250-hour tasks):

Fuel system: replace fuel filter element, check fuel tank for water and sediment.
Air intake: replace outer air filter element, clean and inspect air intake and exhaust louvres.
Cooling system: test coolant concentration with refractometer.
Drive / belts: replace fan belt (or inspect and retension).
Alternator / voltage regulation: check alternator brushes and slip rings, inspect voltage regulator.
Electrical / protection: test ATS operation, test battery under load (CCA), inspect wiring for heat damage, test all protection relays.
Oil analysis: take engine oil sample for laboratory analysis.

Fluid specifications

General fluid specifications for diesel generators (stationary and portable). Capacities vary by generator size and manufacturer.

System	Type / Grade	Approx. Capacity
Engine oil	15W-40 CI-4 / CK-4	8 - 20 L (depending on size)
Coolant	50/50 ethylene glycol	10 - 25 L (system)
Grease	EP2 lithium complex	As required

Specifications are general guidelines. Always refer to the manufacturer's service manual for your specific make and model.

Parts and consumables

Have the following parts and consumables ready before starting the 500-hour service (in addition to all 250-hour parts):

All 250-hour parts (engine oil, oil filter, air filter if replacing, fuel/water separator, EP2 grease, coolant)
Fuel filter element - 1
Outer air filter element - 1
Fan belt - 1 (if replacing)
Oil sample bottle - 1
Coolant test strips - 1 pack
Rags, drip tray and waste oil container

Look up part numbers in the manufacturer's parts manual for your specific make and model before ordering.

How to perform a generator 500-hour service

Complete the full 250-hour service procedure first (engine oil, filter, air filter inspection, fuel/water separator, coolant, load bank test, exhaust, electrical and enclosure checks).
Replace the fuel filter element. Check the fuel tank for water and sediment at the drain point.
Replace the outer air filter element. Clean and inspect air intake and exhaust louvres.
Test coolant concentration with a refractometer. Adjust if outside the 45-55% range.
Inspect and replace the fan belt if it shows cracking, glazing or excessive wear. Retension if the belt is still serviceable.
Check alternator brushes and slip rings for wear. Inspect the voltage regulator for correct output.
Test the automatic transfer switch (ATS) by simulating a mains failure. Verify start signal, load transfer and retransfer.
Load test the battery using a CCA tester. Inspect all wiring and connections for signs of heat damage or loose terminals.
Test all protection relays: over-current, under-voltage and over-speed. Record trip settings and actual trip points.
Take an engine oil sample before draining (or from the drain stream). Label with date, hours and machine ID. Send for laboratory analysis.
Record any defects or recommendations in the notes section. Set the next service due hours. Sign off and update the generator's maintenance log.

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Generator service interval hierarchy

Generator maintenance follows a tiered schedule where each level includes all tasks from the level below. This is called carry-forward or cumulative servicing.

250 hours - Minor service

Engine oil and filter, air filter inspection, load bank test, exhaust and electrical checks. Estimated 1-2 hours.

500 hours - Intermediate service (you are here)

All 250-hour tasks plus fuel filter, outer air filter, fan belt replacement, ATS test, protection relay testing, oil sampling. Estimated 2-3 hours.

1,000 hours / annual - Major service

All 500-hour tasks plus coolant flush, injector and valve clearance checks, turbocharger inspection, inner air filter, insulation resistance test, fuel tank drain, vibration analysis. Estimated 4-6 hours.

In MapTrack, you can configure service schedules by engine hours and receive automatic alerts when each interval is due.

Frequently asked questions

What is included in a generator 500-hour service?: A 500-hour generator service is an intermediate service that includes all 250-hour tasks plus replacing the fuel filter element, replacing the outer air filter element, testing coolant concentration with a refractometer, replacing or retensioning the fan belt, checking alternator brushes and slip rings, inspecting the voltage regulator, testing the automatic transfer switch (ATS) operation, load testing the battery under CCA, cleaning and inspecting air intake and exhaust louvres, inspecting wiring and connections for heat damage, checking the fuel tank for water and sediment, testing all protection relays (over-current, under-voltage, over-speed), and taking an engine oil sample for analysis. It takes approximately 2 to 3 hours.
Why is oil sampling important for generators?: Oil sampling detects engine wear, contamination and oil degradation before they cause failures. A laboratory analysis of the oil sample can identify metal particles (indicating bearing or piston wear), coolant contamination (indicating a head gasket issue), fuel dilution, soot levels and oil condition. Trending results over multiple samples gives early warning of developing problems. This is particularly important for standby generators that may not run regularly but must perform reliably when needed.
How often should a generator ATS be tested?: The automatic transfer switch (ATS) should be tested at every 500-hour service interval. ATS testing verifies that the switch correctly detects a mains power failure, sends a start signal to the generator, transfers the load once the generator reaches stable voltage and frequency, and retransfers to mains when power is restored. A faulty ATS can mean the generator fails to start during a real outage, defeating the purpose of having standby power.
Is the template free to use without MapTrack?: Yes. Download and use the generator 500-hour service procedure for free. Open the file and use your browser's Print, then Save as PDF. No MapTrack account required. If you later want digital service procedures linked to each generator with scheduling by hours, cost tracking and alerts, we would be happy to show you MapTrack.

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