Diesel generator maintenance checklist
The checklist we work to on site, written out so you can print it, put it on the plant room wall and use it. Organised by interval, with a readings log at the end, and deliberately not gated behind a form.
Two things before the tables
They decide whether this checklist is any use to you
Rule one
Your engine manufacturer's schedule governs
The intervals below are the standard shape of a diesel generator maintenance regime and will fit most sets. They do not override the schedule in your engine's own manual, which is written for its oil capacity, filtration and duty.
- Where the two differ, the manual wins
- Send us your schedule and we will follow it
Rule two
A standby set fails on the calendar, not the hour meter
The single most important idea on this page. A set running twenty minutes a month never reaches a running-hours interval, but its battery, coolant inhibitor, rubber and fuel all degrade anyway. Then the mains drop and it is asked for everything.
- Run the calendar intervals whether or not the hours have accrued
- Almost every standby no-start we attend is a set maintained on hours by a site that never put hours on it — see generator not starting
Put the controller in Stop or Manual before any inspection that involves opening a panel, touching a belt or reaching near a fan — a set left in Auto will crank without warning. Isolate the starting battery before working near rotating parts or on the starting circuit. Treat the alternator terminal box and the outgoing breaker as live at all times, including with the engine stopped; anything inside them is isolate, lock off, prove dead work by a competent person. Do not open a hot cooling system, and never add cold water to a hot engine. Exhausts, turbochargers and manifolds stay hot long after shutdown. And never bypass a protection device to complete a test — if a protection stops a test, the protection has found something. The visual and reading tasks below are within reach of a competent plant technician. The electrical testing, the load tests and anything inside the alternator are not.
Interval 1
Daily, or on every visit to the plant room
For sets that run daily. On a standby set, treat these as the weekly walk-round instead.
| Task | What you are looking for |
|---|---|
| Engine oil level | On the dipstick, cold and level. A level that has risen matters more than one that has fallen — that is fuel or coolant getting into the oil. |
| Coolant level | At the cold mark. Do not open a hot system. |
| Fuel level, physically dipped | A failed level sender reading a quarter tank on an empty tank is a routine callout. |
| Leaks under and around the set | Oil, fuel, coolant. Photograph anything new and date it. |
| Controller status | In Auto, no active alarms, and no warnings quietly ignored since last week. |
| Battery charger operating | The charger is on, and its output light or reading is present. |
| Air intake and enclosure louvres clear | Nothing stacked against the radiator, no cardboard, no stored plant. |
| General condition | New noises, new stains, new vibration, anything moved or removed since the last visit. |
| Running readings, if the set is running | Oil pressure, coolant temperature, voltage, frequency, current, hours — logged, not glanced at. |
Interval 2
Weekly
All the daily items, plus the following.
| Task | Notes |
|---|---|
| Test start — run the set to operating temperature | A start that does not reach temperature does the set more harm than good. |
| Record oil pressure, coolant temperature, voltage, frequency and hours during the run | Trends beat snapshots. A reading that has been drifting for three months is a warning. |
| Battery voltage at rest, and while cranking | Voltage that collapses under cranking condemns a battery that reads healthy at rest. |
| Battery terminals and earth strap | Clean, tight, protected. Corrosion here causes more no-starts than anything else. |
| Drain the fuel water separator | Look at what comes out. Water, or a dark slime at the fuel/water interface, changes the whole job. |
| Belts | Tension and condition, on a stopped and isolated set. |
| Coolant hoses | Squeeze cold — soft, spongy, or hard and glazed all mean renewal. |
| Radiator core and enclosure air path | Dust loading. In this climate this is a weekly item, not an annual one. |
| Alarm and event log | Read it. Warnings that nobody actioned are next month's shutdown. |
The weekly test start is the whole regime in one task
If you do nothing else on this page, do that — let it reach temperature, and write down the readings.
Interval 3
Monthly
All weekly items, plus the following.
| Task | Notes |
|---|---|
| Run on load rather than off load | Not optional on a standby set — see the light-load section below. |
| Exercise the changeover: prove the set actually takes the building | A set that starts but never transfers has not been tested. |
| Air filter restriction indicator, and a visual check of the element | Dust here is faster than any published interval expects. |
| Battery electrolyte level, on serviceable batteries | Topped with distilled water only. |
| Charger output voltage measured at the battery terminals | Not at the charger. The reading that matters is the one the battery sees. |
| Coolant condition — inhibitor and freeze/boil protection tested | Inhibitor depletion is invisible, and it is what corrodes liners and cores. |
| Control panel: lamps, indications, emergency stop function tested | Test the E-stop deliberately, on a planned run — not by discovering it does not work. |
| Louvres, dampers and ventilation fans operating | A hot plant room is a derated generator. |
| Exhaust system, silencer, flexible and supports | Corrosion, leaks, cracked flexibles, oily deposits at joints. |
| Anti-vibration mounts | Collapsed, oil-soaked or cracked mounts damage alignment. |
| Fuel tank: level, bund, vent, and water in the bottom | See the fuel section below. |
Interval 4
Six-monthly
All monthly items, plus the following.
| Task | Notes |
|---|---|
| Oil and filter change, and fuel filters, if the manufacturer's calendar interval falls here | Oil degrades by time as well as by hours — oil and filter change. |
| Oil sample sent for analysis | The cheapest look inside an engine that exists. Wear metals, fuel dilution, coolant, soot and viscosity from one bottle. |
| Coolant sample or test | Inhibitor level, pH, contamination. |
| Air filter renewal, or earlier if the restriction indicator says so | |
| Cooling system: radiator core cleaned properly, not just blown over | See radiator and cooling repair. |
| Valve clearances checked, to the engine manufacturer's interval | A tappet check is cheap; a burnt valve is not. |
| Hoses, clips and belts renewed on condition | |
| Battery capacity assessed, not just voltage | UAE heat shortens battery life materially. A battery in its fourth summer here is on borrowed time. |
| Charging alternator output verified with the set running | |
| Terminal box and panel connections: thermographic survey or torque check | Loose connections are heat, and heat is the failure. |
| Written condition report filed, with the readings trended |
Interval 5
Annual
All six-monthly items, plus the work that needs instruments.
| Task | Notes |
|---|---|
| Load test the set properly — real load steps, up to full rated load, with voltage, frequency, temperatures and pressures recorded at each step | The only test that proves the set will do the job. Load bank testing. |
| Coolant renewed to the engine manufacturer's specification and interval | Correct inhibitor package, correct mix. Not water. |
| Fuel system: tank inspected internally, water and sludge removed, fuel polished or replaced as required | See generator fuel system service. |
| Injectors assessed; tested and calibrated on a bench where hours or symptoms justify it | |
| Turbocharger shaft play and condition checked | |
| Insulation resistance test on the alternator stator and rotor | A trend across years is what makes this number useful. |
| Protection settings verified against the machine and the installation | Not against a factory default nobody has looked at since commissioning. |
| Changeover / AMF panel fully function tested, including on a genuine simulated mains failure | |
| Earthing and bonding inspected | |
| Governor and speed control response checked | |
| Full written report, with all readings against the previous year's | This is the document that turns maintenance into evidence. |
The part that finds faults
The readings log
The tables above are tasks. This is what catches a fault before it becomes a breakdown. Copy it, one row per run, and keep it with the set.
| Date | Hours | Ambient °C | Oil press. | Coolant temp. | Volts L1/L2/L3 | Hz | Amps L1/L2/L3 | kW | Battery V | Fuel level | Notes / alarms | By |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Why the log beats the checklist
A single oil pressure reading tells you almost nothing. Twelve monthly readings showing pressure falling steadily on a hot engine tell you the bottom end is wearing, months before an alarm does. The same is true of coolant temperature creeping up as a core loads with dust, of battery voltage falling each summer, and of a current imbalance growing as single-phase loads are added to one phase. Record the ambient temperature too — in this climate a coolant temperature reading without an ambient beside it is not comparable to last month's. Any reading that has moved consistently in one direction for three consecutive entries deserves a look, even while it is still inside its limit.
What it is for
The three things this checklist exists to prevent
- Battery failure
The commonest cause of a standby set failing to start in the UAE, by a wide margin. Heat accelerates the chemical wear inside a lead-acid battery — harder on it than cold is — and a charger that has quietly failed or been unplugged leaves a set that looks ready and is not. That is why battery voltage, terminals, charger output and battery age appear at four different intervals above.
- Fuel degradation and water
A warm, part-empty tank makes condensation, condensation makes water, and water in a diesel tank in this climate makes microbial growth. It blocks filters, corrodes tank floors and pushes abrasive debris through injection equipment worth far more than the fuel. Keep tanks full, drain the separator weekly, and look at what comes out.
- Light-load running and wet stacking
A standby set that runs a short monthly test off load never reaches proper cylinder temperatures. Unburnt fuel and soot accumulate, bores glaze, the exhaust weeps oily deposits, and the set slowly loses its ability to take load — discovered on the one day it matters. The cure is running on real load, on a schedule, and proving it annually against a load bank.
Where it stops
What this checklist cannot do
It is an honest checklist, so it should say where it stops. It will not find an interturn short in a stator winding, a crankshaft journal approaching its bottom undersize, an injector delivering the right quantity at the wrong pattern, or a controller whose protection settings were configured wrongly at commissioning and have never been questioned.
Those need instruments — insulation resistance testing, a bench, a load bank, micrometers, diagnostic software — and they are why an annual visit by someone with that equipment is worth more than twelve good walk-rounds.
- Yours
Visual checks, fluid levels, the test start, the readings and the log. The most valuable maintenance a set gets, and it is site work.
- Ours
Annual electrical testing, the load test, injection and valve work, and anything inside the alternator or the terminal box.
- Together
Split it that way and the set is covered week to week and proved once a year. That is preventive maintenance, on a schedule.
Common questions
Servicing, answered
How often should a standby generator be serviced?
To the engine manufacturer's schedule, on whichever comes first, hours or calendar — and on a standby set that is almost always the calendar. A full service at least annually, with the interim checks above at their intervals, is the shape most sets need. A set that genuinely runs hours, on prime duty, is governed by the hour meter instead.
How long should a monthly test run be?
Long enough to reach normal operating temperature and stabilise there, and on load rather than off load. A short off-load run does more harm than no run at all: it wets the exhaust, glazes the bores and leaves the set colder than it started. If the building cannot take the set on load monthly, that is an argument for load bank testing rather than an argument for shorter runs.
Can I do this checklist myself, or do I need an engineer?
The visual checks, the readings, the fluid levels, the test start and the log are all site work, and doing them well is the most valuable maintenance a set gets. What needs an engineer is the annual electrical testing, the load test, the injection and valve work, and anything inside the alternator or the terminal box. Split it that way and you get the best of both.
Do you provide a maintenance checklist and report after a service visit?
Yes. Every attendance leaves a written record — readings taken, work done, parts fitted, condition noted, dated and signed — because in most cases our customer has to hand that to their own client or their own auditor. A verbal "it's fine" is not a maintenance record.
My set has very low running hours. Does it still need servicing?
Yes, and this is the misunderstanding that causes the most standby failures. Oil oxidises, coolant inhibitor depletes, rubber perishes, fuel degrades and batteries age on the calendar regardless of hours. An hour meter reading 40 after three years does not mean the set is three years newer than it is.
Do you offer maintenance contracts?
Yes — scheduled servicing scoped against your equipment and your site, with priority when something fails between visits. Terms are agreed against the sets and the conditions rather than sold as a package: see generator AMC and annual maintenance contracts.
Put it on a schedule
Send your engine and alternator data plates, the running hours and what the sets feed, and we will tell you what interval regime that equipment actually needs. Open 7 days, 07:00–20:00.