Last verified: October 1, 2026
Short answer: for Generac’s air-cooled home standby generators, change the oil and oil filter after the first 25 hours of running (the break-in), then every 2 years or 200 hours, whichever comes first. In cold climates (below 40°F) or when the generator runs continuously in hot weather (above 85°F), shorten that to every year or 100 hours. After break-in, Generac recommends its own full synthetic 5W-20 Gaseous Engine Oil (GEO), and lists a few other oils that are acceptable only in an emergency. Other brands publish their own requirements, so treat your owner’s manual as the final word.
Which oil Generac recommends
| Oil | Temperature range | Use |
|---|---|---|
| 5W-30 (conventional) | Full operating range | Factory fill and break-in only |
| Generac synthetic 5W-20 GEO | Full operating range | Recommended after break-in |
| Synthetic 5W-30 | Full operating range | Acceptable (emergency) |
| 10W-30 | −10°F to 40°F | Acceptable (emergency) |
| SAE 30 | Above 32°F | Acceptable (emergency) |
Source: Generac: What type of oil should I use in my home backup generator? Generac adds two important notes: emergency alternatives should meet API service class SJ, SL or better, and you should not switch to synthetic oil until after the initial 25-hour break-in oil change.
Why a “gaseous engine” oil?
Standby generators burn natural gas or propane rather than gasoline. Gaseous fuels burn hotter and cleaner, and engines that run on them can benefit from oils formulated for those conditions. That is why Generac sells an oil specifically for its gaseous-fuel engines and treats general-purpose automotive oils as a fallback. Whichever brand you own, look for the oil specification in the manual rather than picking whatever is on the shelf.
How often to change it
| Situation | Oil and filter change |
|---|---|
| New generator | After the first 25 hours of operation (break-in) |
| Normal conditions | Every 2 years or 200 hours |
| Cold climate (below 40°F) or continuous running above 85°F | Every year or 100 hours |
| Larger service | Every 4 years or 400 hours: oil and filter plus air filter and spark plugs |
| During a long outage | Check the oil level daily; change when the hours since the last service reach the interval |
Intervals from Generac’s owner’s manual for its 60 Hz air-cooled generators and its continuous-use guidance. The weekly self-test only adds a few minutes of running each week, so for most owners the time limit (one or two years) arrives long before the hour limit. Long outages change that quickly.
How fast run hours add up
Hours matter more than most owners realize. A quick calculation shows why:
| Running pattern | Hours added | What it means |
|---|---|---|
| Weekly self-test, about 5–12 minutes for a year | Roughly 4–10 hours | Barely moves the counter |
| Three outages of 8 hours | 24 hours | Still far from 200 |
| One 4-day hurricane outage | 96 hours | Almost half the normal interval; the full interval in hot weather is 100 hours |
| One 9-day outage | 216 hours | Past the 200-hour interval: an oil change is due during or right after the outage |
Your generator’s controller (and the app on connected models) shows total run hours. Write down the reading at each service so you always know how many hours have passed.
Checking the oil level
Generac’s manual says the oil level should be checked daily when an outage keeps the generator running for long periods, and before expected use. The manual’s procedure involves letting the generator cool down, switching the main utility disconnect and the generator’s main breaker off, pressing the controller’s OFF button and waiting a few minutes before pulling the dipstick. Follow your own model’s steps exactly, because a standby generator in Auto can start by itself at any time.
Do it yourself or call the dealer?
Reasons to do it yourself
- You are comfortable with basic engine maintenance and following a lock-out procedure.
- You want to be able to change oil during a long outage when dealers are overloaded.
- You keep receipts and a dated log so warranty coverage is protected.
Reasons to use the dealer
- The job involves shutting off utility power to the transfer switch and working inside the enclosure.
- A technician also checks the battery, wiring, transfer switch and controller software while there.
- The dealer keeps an official service record, which can help with warranty claims.
Many owners split the difference: a dealer service on schedule, plus the ability to check and top up oil themselves during long outages. If you are weighing a service contract, see Is a Generator Maintenance Plan Worth It?
Common oil mistakes
- Switching to synthetic during break-in. Generac specifically says to wait until after the 25-hour change.
- Using whatever oil is in the garage. Check the viscosity and API class against the manual; some grades are only for certain temperature ranges.
- Overfilling. Too much oil is listed in Generac’s troubleshooting table as a cause of high oil consumption. Fill to the mark, no higher.
- Forgetting the filter. The schedule calls for oil and filter together.
- Losing track of hours. After a long storm season, the next change may be due much sooner than the calendar suggests.
Keep a storm kit
Before hurricane or winter storm season, keep the right amount of the recommended oil, a spare oil filter, a funnel and rags at home. Look up your model’s oil capacity in the manual. If a long outage pushes the generator past its interval, you can keep it healthy until a technician is available. See How to Prepare Your Generator Before Hurricane Season.
Frequently asked questions
Can I use regular car oil?
Only as an emergency option, and only if it matches one of the grades Generac lists as acceptable and meets API SJ, SL or better. The recommended oil after break-in is Generac’s 5W-20 synthetic gaseous engine oil.
My generator only runs for the weekly test. Do I still need to change the oil?
Yes. Oil ages even when the engine runs little, which is why the schedule has a time limit (every 2 years, or every year in cold or hot-weather duty) as well as an hour limit.
What if the oil level is low after a long outage?
Top it up to the full mark with the correct oil once the generator is safely shut down and cool. If the generator uses a lot of oil, Generac’s troubleshooting guide lists causes such as overfilling, a defective breather, the wrong oil, leaks or a restricted air filter; have a dealer check it.
Bottom line
Follow the break-in change at 25 hours, then every 2 years or 200 hours (every year or 100 hours in extreme temperatures), use the oil your manufacturer recommends, check the level daily during long outages and keep a record of hours and services. For the full schedule, see our standby generator maintenance checklist.