Diesel Generator Service Intervals

A diesel generator only matters on the day the power’s out — and that’s exactly the day a neglected one won’t start. Generators fail differently than other diesels: many barely accumulate hours, so they need calendar-based care as much as hour-based.

Service by hours AND by calendar

A prime-power generator running daily follows hour intervals like any diesel. But a standby unit that runs a few hours a month will hit a year long before it hits an oil-change hour count — and fuel, coolant, and seals age on the calendar regardless. Service whichever comes first.

Typical intervals

Interval	Service
Weekly/monthly	Exercise under load; check oil, coolant, fuel, battery
Every ~250 hrs or annually	Oil and filter, fuel filters, air filter, inspect belts/hoses
Annually	Coolant test, full inspection, load-bank test
2 yrs / per coolant spec	Coolant change

Always confirm against the unit’s manual.

Exercise it under load

The most important habit is running the generator regularly, under load — not just a no-load idle. Light exercising at no load causes “wet stacking,” where unburned fuel and soot accumulate in the exhaust because the engine never reaches proper operating temperature. Run it loaded (a transfer switch test or load bank) so it gets hot and burns clean.

Fuel is the usual culprit

Diesel fuel degrades, absorbs water, and grows microbial growth (“diesel bug”) in storage — exactly the conditions in a standby tank that sits in Lowcountry humidity. Keep tanks full to limit condensation, use a stabilizer/biocide as needed, drain water separators, and polish or test fuel periodically. Bad fuel is the number-one reason standby units fail to carry the load.

Batteries fail at the worst time

A weak starting battery is the most common no-start. Check terminals and electrolyte (if applicable), keep it on a maintainer, and replace on a schedule rather than waiting for failure.

Don’t skip the annual load-bank test

A load-bank test verifies the generator can actually produce rated power and burns off wet-stacking buildup. It’s the only way to know it’ll perform when it matters — a unit that “runs fine” at no load can still fail under real demand.

For standby power you’re counting on, our shop can set up a service and load-test schedule so the generator is ready the day you need it — not a surprise.