Genset Maintenance Schedule: Daily Checks, 500-Hour Service and the Log Book

How often should a genset be serviced?

A genset is serviced by running hours, read off the hour meter on its control panel, with a calendar limit as a backstop. Whichever comes first decides the service. A set that runs 10 hours a day on a building site reaches 500 hours in about seven weeks. A standby set at a site office may take a year to log the same hours, and it still needs its yearly service.

The figure is not the same for every set. It changes with the maker, the engine and the emission class. CPCB IV+ is the emission standard that new genset engines up to 800 kW have had to meet since 1 July 2023. The table below collects what the makers’ own documents say, as we read them in November 2026.

So the honest answer is “read your set’s manual”. If you do not have it, plan on the shorter figure until the dealer confirms the longer one. Kirloskar and Greaves tie their intervals to their own oils, and the Doosan letter says outright that the interval shortens when the oil or the diesel is of poorer quality.

What should you check on a genset every day?

The daily check takes a few minutes and is done before starting, with the set cold. It catches most of the faults that stop a set in the middle of a pour or a night shift.

1. Engine oil level on the dipstick, between the two marks. Top up with the same grade. A set that needs topping up more and more often is telling you something.
2. Coolant level in the radiator or expansion tank. Open the cap only on a cold engine; hot coolant is under pressure and scalds.
3. Fuel level, and water in the fuel. Drain the water from the bowl of the fuel/water separator, the filter that catches water before it reaches the pump. Doosan lists this as a daily job.
4. Air filter. Squeeze the rubber dust valve on the pre-cleaner, if the set has one, so dust can fall out. On a dusty site this filter chokes long before its hours are up.
5. Fan belt tension and any cracks on it; the fan belt guide shows how tight a belt should be.
6. Battery terminals clean and tight, no white powder, no swollen case.
7. DEF level on a CPCB IV+ set that uses diesel exhaust fluid, the urea solution that cleans the exhaust, and no leaks on its lines. Greaves lists it with its daily and monthly checks.
8. A walk round for oil or diesel leaks, loose bolts, frayed wires and anything blocking the air vents of the canopy.

Once the set is running and loaded, look at the panel: voltage, frequency (50 Hz on an Indian set), oil pressure and coolant temperature. Write them in the log.

What is done at the 250 or 500-hour service?

This is the main “oil service”. It is the one most sites mean when they say the set is due.

• Change the engine oil and the oil filter. Drain the oil while the engine is still warm, because warm oil drains more completely.
• Change the fuel filter and the element in the water separator. Doosan’s letter gives the separator element six months or 500 hours, sooner if the diesel is dirty.
• Clean or change the air filter element.
• Check the coolant level and the hoses, and look for dust packed into the radiator fins.
• Check the battery voltage and the charging alternator output.
• Check that the protections on the controller still work, such as low oil pressure and high coolant temperature.

A new set gets an early first service. The Doosan letter changes oil and filter at 100 hours on a new or rebuilt engine in its smaller sets, and Greaves sets the first valve clearance check at 60 hours. Ask the dealer for the first-service hour when the set is delivered and write it on the first page of the log.

Use the oil grade the maker names. The engine oil guide explains grades such as 15W-40 and the API class printed on the can.

What is done once a year or at 1,000 to 2,000 hours?

The longer checks deal with parts that wear slowly: valves, the cooling system, the fuel injection pump and the electrics. The makers we read list these jobs, though each puts them at its own hour mark.

Figure 1: The service ladder on a typical diesel genset

Combined from the Doosan Portable Power service letter SL 30003 (March 2011) and the Greaves CPCB IV+ note (August 2025). Your set’s manual decides the exact hour for each job.

Greaves adds two jobs to its yearly list that site owners often forget: cleaning out the fuel tank, where water and sludge settle at the bottom, and cleaning the exhaust silencer. On a CPCB IV+ set the silencer may carry an exhaust catalyst (Cummins prints a “DOC”, diesel oxidation catalyst, in the silencer of its small sets), so leave that part to the authorised dealer.

The self motor and charging alternator are checked at this stage. A set that cranks slowly on a cold morning usually has a tired battery or starter, not an engine fault. Coolant life is set by the type in the system; the coolant guide explains the types and how often each is changed.

Does a genset that runs only a few hours a month still need service?

Yes. A standby set ages by the calendar even when the hour meter barely moves. Oil takes in moisture, diesel in the tank collects water, rubber hoses harden and the battery drains on its own. That is why every maker in the table pairs the hours with months.

Kirloskar’s service terms show how the visits scale with use: 4 health checks a year for a set that runs less than 500 hours a year, 6 for 500 to 1,000 hours, and 12 for more. Cummins builds an “exerciser scheduler” into the controller of its small CPCB IV+ sets, which starts the set on a timer so it runs regularly.

When you test-run a standby set, put real load on it. A set that runs for half an hour with nothing connected does more harm than good, for the reason in the next section.

Why does light load harm a diesel genset?

A diesel engine running with very little load does not get hot enough to burn all its fuel. The unburnt fuel passes into the exhaust as a black, oily ooze around the manifold and turbocharger. This is called wet stacking, from “stack”, the exhaust pipe.

The Bureau of Energy Efficiency DG set chapter says engine loading should be kept above 50% and that steady loads suit a set best. When a lightly loaded set is finally given heavy work, it often blows black smoke while it burns off what has built up.

Two things prevent it. Size the set close to the real load; the generator size calculation walks through it. Then run test runs on load. An oversized set also wastes diesel, as the genset fuel consumption guide shows with maker figures.

What signs mean a genset needs attention before its service is due?

Hours are the plan, but the set will tell you when something has gone wrong in between. Mahindra Powerol lists seven warning signs; this table puts them next to the likely cause and the first thing to check.

Smoke colours can also come from fuel injectors that drip instead of spraying. Injector and fuel pump work is a dealer job.

What should a genset log book record?

A log book is the single most useful maintenance tool on a site genset. It tells you when the next service falls due, and it shows a fault coming before it stops the set. Keep one page per day, or one line per run on a standby set:

• Date, operator’s name, and start and stop times.
• Hour meter reading at start and stop.
• Load: kW or amps per phase, voltage and frequency, read once the set is loaded.
• Oil pressure and coolant temperature from the panel.
• Diesel added (litres) and oil topped up (litres).
• Any fault, warning or unusual smoke, and what was done.
• Service done, by whom, and the hour reading for the next one.

Two numbers from the log are worth working out every week. Units per litre (kWh divided by litres of diesel) shows if the set is burning more for the same work; the fuel guide gives normal figures by size. Oil topped up per 100 hours shows engine wear early. The BEE chapter’s sample monitoring format records both fuel and lube oil per unit generated for the same reason.

A good log also settles arguments on a hired set, about hours billed and diesel used, and it adds to resale value when you sell a set you own.

Who services a hired genset, and what should you agree first?

On a hired set, the hire firm normally owns the service, but the site still does the daily check and keeps the log. Agree four things in writing before the set arrives:

1. Who does the service at the hour mark, and how soon after a call.
2. Who pays for oil, filters and coolant at that service.
3. How hours are read and billed: from the hour meter, with a reading signed at delivery and at return.
4. What happens if the set breaks down: a replacement set, and within how many hours.

For a set you own, makers sell yearly service contracts through their dealers. Kirloskar’s, for example, lets you choose the number of visits and covers the labour and visits, while you pay for oil and parts. Read what is excluded before you sign.

For machines and site equipment on hire, see what is available on rent near your project. Every page on types, sizes and rules for site sets is collected in the genset guide, starting with the diesel generator for a construction site.