Quick answer
A generator that sits unused is the one most likely to fail when the power goes out. Run it on a regular schedule, keep fuel fresh, change the oil and filters on the intervals in your owner’s manual, and keep the battery healthy. Before outage season, do a full walkthrough. Standby generators also need a yearly service by a qualified technician. The calendar below gives you a structure. Your owner’s manual sets the actual intervals for your model, and it always wins when the two differ.
Why a schedule matters
Most generator failures during an outage trace back to the months before it. Gasoline goes stale and gums up the carburetor. Batteries lose charge. Oil breaks down or runs low. Mice nest in enclosures, and filters clog. None of these show up until you pull the cord or the automatic switch calls for power. A simple calendar turns maintenance into a few minutes a month instead of a scramble in the dark.
This page is about routine upkeep. For cold-weather prep, see the Winter Generator Guide. For where to run the generator safely, see Where to Put a Generator.
Two kinds of intervals: calendar and hours
Manufacturers usually give maintenance intervals two ways: by time (every month, every year) and by run hours (every so many hours of operation), whichever comes first.
- Calendar intervals matter most for generators that sit unused. Oil, fuel and batteries age even when the engine doesn’t run.
- Hour intervals matter most during and after long outages, when a generator can run for days and reach its next service point quickly.
Many generators have an hour meter, and standby controllers usually track hours. If yours doesn’t, keep a simple log of when it ran and for how long. After a long outage, check the log against your manual before you put the generator away.
The calendar at a glance
| When | Portable generators | Standby generators |
|---|---|---|
| Monthly | Start and run under a light load; check oil level; look for leaks, damage, and pests | Confirm the automatic exercise ran; check the controller for alerts; look around the enclosure |
| Every 3 months | Check the air filter; inspect cords and plugs; rotate stored fuel | Check that vents and the area around the unit are clear; check for pests |
| Before outage season | Full walkthrough (below); fresh stabilized fuel; battery check for electric start | Book the annual service; check the battery; test the transfer switch with your installer’s guidance |
| Every year | Oil change, spark plug, and air filter on the manual’s schedule | Professional service: oil, filters, plugs, battery test, transfer switch check |
| After a long outage | Check run hours against the manual; change oil if due; refresh fuel | Check hours; book service if an interval was reached; check the controller log |
Monthly: the exercise run
Portables
Start the generator and let it run under a light load, such as a work light or a small appliance, for the time your manual suggests. Running it under load is better than idling with nothing plugged in, because it brings the engine up to temperature and moves fuel through the system.
While it runs:
- Listen for surging, sputtering, or unusual noise.
- Check that the outlets work.
- Look for fuel or oil leaks underneath.
Before you start, check the oil level with the engine off and on level ground. Run it outdoors at your planned spot, never in a garage or shed.
Standbys
Most standby generators run an automatic exercise on a set schedule, often weekly or every other week, depending on the model and settings. Your job is to confirm it’s happening:
- Check the controller display or app, if your model has one, for the last exercise and any alerts.
- Listen for it on its scheduled day.
- Walk around the enclosure and look for leaves, debris, nests, or anything blocking the vents.
If the exercise isn’t running or the controller shows a warning, contact your dealer rather than resetting it repeatedly.
Every three months
Air filter
Check the air filter and clean or replace it as your manual describes. Dusty, dirty or rural sites may need more frequent checks.
Cords, plugs and connections (portables)
Inspect extension cords and the generator cord for cuts, crushed spots, or damaged plugs. Check that the inlet box cover closes and seals. Replace damaged cords rather than taping them.
Fuel rotation
Gasoline doesn’t keep indefinitely, even with stabilizer. Use your oldest stored fuel in a car or lawn equipment and replace it with fresh, stabilized fuel. Follow the stabilizer label for how long it protects fuel. Check propane tank levels, and check that natural gas lines and the meter area are clear.
Pests
Mice and insects like generator enclosures and stored portables. Look for nests, droppings, or chewed wiring. Keep the storage area tidy and sealed.
Maintenance by fuel type
Gasoline
Gasoline is the fuel most likely to cause trouble after months of storage. Stabilize it when you buy it, store it in approved containers in a spot your local fire code allows, and rotate it on your three-month check. If a portable starts hard after storage, stale fuel is the first suspect. Drain and replace it before assuming a bigger problem.
Propane
Propane doesn’t go stale, which makes it easier to keep ready. The maintenance work is around the tank and connections: check tank levels, schedule deliveries before the busy season, keep the tank and regulator clear of debris and snow, and have your supplier inspect the tank and lines on their schedule. If you smell gas, leave the area and call your supplier or 911 from a safe distance.
Natural gas
With natural gas there’s nothing to store, but the meter, regulator and line need to stay clear and undamaged. Keep landscaping, stored items and snow away from them. Your installer or technician checks the gas connection to the generator during the annual service.
Dual-fuel and multi-fuel
If your generator runs on more than one fuel, exercise it on each fuel it supports from time to time, following your manual, so you know each path works. Keep up the fuel-specific checks for every fuel you rely on.
Build a small maintenance kit
Keeping the right items together makes the monthly and seasonal checks quick. Your manual lists the exact parts for your model, but a typical kit includes:
- The owner’s manual, or a printed copy of the maintenance section
- The oil grade or grades your manual lists, plus a funnel and rags
- A spare air filter and spark plug
- A spark plug wrench that fits your model
- Fuel stabilizer and approved fuel containers (gasoline models)
- A battery maintainer, if your manual recommends one
- A flashlight or headlamp
- This page’s printable log and a pen
Store the kit with the generator or right beside it, so nobody has to hunt for parts during an outage.
Before outage season: the full walkthrough
Do this once a year before the season when outages are most likely where you live. In many areas that means before hurricane season, before winter, or both.
- Read the maintenance section of your owner’s manual again. Note anything you’ve missed.
- Change the oil if it’s due by calendar or hours, using the grade your manual lists for the coming season’s temperatures.
- Replace or clean the air filter and check the spark plug on the manual’s schedule.
- Refresh fuel. Fresh stabilized gasoline, a full propane tank, or a clear natural gas meter area.
- Test the battery on electric-start portables and on every standby. Replace an aging battery before it fails.
- Run it under load for longer than a monthly exercise, powering a few of the circuits or appliances you’d actually use. See your Critical Load Worksheet.
- Check the connection. For portables, test the inlet, interlock or transfer switch the way your electrician showed you. For standbys, confirm the transfer switch works as your installer described. See Transfer Switch vs Interlock.
- Test CO alarms on every level of your home.
- Restock spares: oil, an air filter, a spark plug, and any fuses your manual lists.
- Walk your placement plan and check the spot is still clear, level and dry.
Every year: the standby service
Standby generators benefit from a yearly service by a qualified technician, and some warranties require it. A typical visit includes an oil and filter change, spark plugs, a battery test, inspection of belts, hoses and wiring, a controller check, and a transfer switch test. Ask what’s included before you book. If you’re still comparing installers, ask each one about maintenance plans and what they cover. The Generator Installer Quote Checklist includes this question.
Portables don’t need a technician visit for routine upkeep, but a yearly oil change, spark plug and air filter on the manual’s schedule keeps them reliable. If a portable has been hard to start or runs rough, a small-engine shop can clean the carburetor.
After a long outage
Long outages can put many hours on a generator in a few days.
- Check the hour meter or your log against your manual’s service intervals.
- Change the oil if it’s due, and check the air filter.
- Refresh fuel if you dipped into old stock.
- For standbys, check the controller log and book service if an interval was reached.
- Write down anything that went wrong, like a hard start, a stall or a tripped breaker, so you can fix it before the next one.
Storage between seasons (portables)
If your portable will sit for months:
- Follow your manual on fuel: either run the carburetor dry or keep the tank full of stabilized fuel. Manufacturers differ.
- Store it somewhere dry and ventilated, away from living spaces and ignition sources.
- Keep electric-start batteries charged with a maintainer if your manual recommends one.
- Cover it with a breathable cover to keep dust out.
- Keep up the monthly exercise run even in storage season.
Signs it needs attention now
Some problems shouldn’t wait for the next scheduled check. Stop using the generator and fix the cause, or call a technician, if you notice:
- A fuel or oil leak, or a fuel smell around the unit
- Surging, stalling, or power that drops in and out under a normal load
- Black or unusual smoke, or a burning smell
- A standby that misses its exercise, shows a fault code, or won’t transfer power
- Damaged cords, a cracked inlet box, or scorch marks on a plug
- A low-oil shutdown more often than usual
Write the symptom in your log, including when it happened and what was running, so the technician has something to go on.
Common maintenance mistakes
| Mistake | What happens | Better habit |
|---|---|---|
| Never running it until the power goes out | Stale fuel, dead battery, hard or no start | Monthly exercise run under light load |
| Leaving untreated gas in the tank for months | Varnish in the carburetor | Stabilize fuel and follow your manual’s storage method |
| Skipping oil checks during long outages | Low-oil shutdown, or engine wear | Check oil at the intervals your manual gives, engine off |
| Ignoring standby controller alerts | A small issue becomes a failed start | Check alerts monthly and call your dealer |
| Running the exercise in the garage | Carbon monoxide risk | Always outdoors at your planned spot |
| Not tracking run hours | Missed service after a big outage | Hour meter or a simple log |
Two example routines (outlines)
These are structures to adapt, not prescriptions for a specific model.
Routine 1: Portable on an inlet and interlock
- First Saturday of each month: oil check, run under a light load at the marked spot, check outlets and look for leaks.
- Every three months: air filter check, cord and inlet inspection, fuel rotation.
- Before outage season: full walkthrough, including an interlock test and a longer run on real circuits.
- After any long outage: hours check, oil change if due, fuel refresh, notes on anything that went wrong.
Routine 2: Standby on propane or natural gas
- Monthly: confirm the automatic exercise ran, check controller alerts, walk around the enclosure.
- Every three months: clear vents and surroundings, check for pests, check the propane level if applicable.
- Before outage season: book the annual service, test the battery, confirm the transfer switch operation with your installer’s guidance.
- After any long outage: check hours and the controller log, and book service if an interval was reached.
Printable maintenance log
Copy this into a notebook or print it and keep it with the generator.
| Item | Done? | Date | Notes |
|---|---|---|---|
| Monthly exercise run done (date, minutes, load used) | ☐ | ||
| Oil level checked | ☐ | ||
| No leaks, damage or pests found | ☐ | ||
| Standby exercise confirmed and no controller alerts | ☐ | ||
| Air filter checked (every three months) | ☐ | ||
| Cords, plugs and inlet inspected (every three months) | ☐ | ||
| Stored fuel rotated, or propane level checked (every three months) | ☐ | ||
| Pre-season walkthrough completed | ☐ | ||
| Oil, filter and spark plug changed on schedule (date and run hours) | ☐ | ||
| Battery tested or replaced | ☐ | ||
| Standby annual service done (date, technician) | ☐ | ||
| CO alarms tested | ☐ | ||
| Notes from the last outage addressed | ☐ |
FAQ
How often should I run my generator?
Follow your manual. A common approach for portables is a monthly run under a light load. Standbys usually exercise themselves on a weekly or biweekly schedule.
Do I need to change the oil if I never used the generator?
Oil ages even when the engine doesn’t run, so most manuals give a calendar interval as well as an hour interval. Change it on whichever comes first.
Can I just let it idle with nothing plugged in?
A light load is better, because it brings the engine up to temperature and exercises the electrical side. Check your manual’s recommendation.
Does my standby really need a yearly service?
Many manufacturers recommend it, and some warranties require it. Check your warranty terms and ask your installer.
What should I do after a multi-day outage?
Check run hours against your manual, change the oil if it’s due, refresh fuel, and fix anything that went wrong before you need it again.