Generator Maintenance Checklist: What to Do and When

Here’s the stat that should scare you: most generator failures during real outages aren’t mechanical breakdowns. They’re maintenance failures. Dead starting battery. Gummed-up carburetor from stale gas. Oil that turned to sludge two years ago. The machine was fine — the owner wasn’t.

Generators are the ultimate “works until it doesn’t” equipment. They sit for months, then get asked to run hard for days. That duty cycle punishes neglect more than almost any other machine you own. The good news: the maintenance that matters is simple, cheap, and mostly DIY.

Why Maintenance Is the #1 Killer

A generator that runs weekly stays healthy. A generator that sits for 18 months develops problems silently:

• Batteries self-discharge. A standby’s starting battery dies in 3–5 years even if the generator never runs. When the outage hits, the ATS calls for a start and gets a click.
• Gasoline degrades. Untreated fuel varnishes the carburetor in months. The engine cranks but never catches — or surges and dies under load.
• Oil absorbs moisture. Condensation builds up in a crankcase that never gets hot. Old oil loses its protective properties and can sludge.
• Exercise cycles mask problems — or reveal them. A standby that exercises weekly will throw a fault code for a failing battery or low oil. A portable that never gets started tells you nothing until the storm.

The fix for all of this is a schedule. Here’s the one that actually matters.

Standby Generator Schedule

Weekly: automatic exercise (5–12 minutes)

Your standby does this itself — most units (Generac, Kohler) ship with a weekly exercise cycle, usually 5–12 minutes at low RPM. Leave it enabled. This is the single most valuable maintenance feature on a standby: it circulates oil, charges the starting battery, and runs a self-diagnostic.

Your job: glance at the unit once a month to confirm it’s actually exercising (listen for it on its scheduled day) and check the controller display for fault codes or warnings. A unit that quietly stopped exercising months ago is a unit that will fail you.

Monthly: visual inspection (5 minutes)

• Check for fault codes or warning lights on the controller.
• Look for oil spots or coolant puddles under the unit.
• Confirm the area around the unit is clear — 3+ feet of clearance on all sides, no mulch piled against it, no rodent nests in the enclosure (mice love generator housings; they chew wiring).
• If propane: check the tank gauge. Don’t discover you’re at 10% during an outage.

Annually: the real service (DIY or tech, ~1 hour)

Do this every year or every 100–200 run hours, whichever comes first:

• Oil and oil filter change. Air-cooled standbys typically take 2–4 quarts of 5W-30 synthetic (check your manual — Generac specifies its own oil but quality synthetic 5W-30 meets the spec). This is the highest-value maintenance item on the list.
• Air filter. Inspect; replace if dirty. A clogged air filter chokes the engine and wastes fuel.
• Spark plugs. Replace annually on most air-cooled units. They’re $5–$10 each and take minutes.
• Check coolant (liquid-cooled units only — most residential air-cooled units don’t have coolant).
• Inspect the battery terminals for corrosion; clean and tighten.
• Check the transfer switch. With the generator running, verify it actually transfers load. Some owners never test this until the outage.

Every 2–3 years: battery replacement and valve check

• Replace the starting battery every 3–5 years, proactively. Don’t wait for it to die. A Group 26R or U1 battery (depending on model) costs $60–$120. Mark the install date on the battery with a paint pen.
• Valve lash adjustment roughly every 2–3 years or per the manual’s hour interval. This one usually needs a tech — it’s fiddly, and getting it wrong causes hard starting and power loss.
• Fuel system: for propane/NG standbys, have the tech check the fuel regulator and lines for leaks during the valve service.

Portable Generator Schedule

Portables don’t exercise themselves, so the schedule is on you.

Every use: the basics

• Check oil level before every start. Most portables hold under a quart — running low on oil will seize the engine, and low-oil shutdown sensors don’t always save you.
• Inspect for fuel leaks and damaged cords.

Every 50–100 run hours (or annually): oil change

Portable generator oil changes are the most-skipped maintenance in existence. The interval is short — 50–100 hours depending on the model (check your manual; break-in change is usually at 20–25 hours on a new unit). A weekend-long outage can eat half that interval. Use the weight your manual specifies (usually 10W-30 conventional or 5W-30 synthetic).

For ~$8 in oil and 15 minutes, this is absurdly cheap insurance.

Fuel system: stabilizer or run dry

Pick one religion and stick to it:

• Stabilizer route: add Sta-Bil or equivalent to fresh gas at purchase, run the generator 5 minutes to circulate it through the carburetor. Good for 12–24 months of storage.
• Run-dry route: shut off the fuel valve and let the engine run until it dies, draining the carburetor bowl. Best for storage over 6 months.

Either works. What doesn’t work is parking a generator with untreated gas in the tank “just for the winter” and finding varnish in spring.

Monthly: start it

Start the portable once a month and run it 10–15 minutes with a load — plug in a space heater or a couple of work lights. Unloaded running doesn’t fully exercise the generator end or burn off moisture. This monthly run is what keeps the carburetor clear and tells you about problems while there’s still time to fix them.

The Battery Section (Read This Twice)

Generator starting batteries die quietly and completely. Here’s what to know:

• Lifespan is 3–5 years, period. Heat, cold, and sitting discharged all shorten it. Budget for replacement on schedule, not on failure.
• Use a trickle charger / battery maintainer on standby units if the built-in charger isn’t keeping up (the controller display usually shows charging status). For portables with electric start, a $30 battery maintainer plugged in during storage season pays for itself the first time the generator actually starts.
• Portables with pull-start only: no battery to worry about — one genuine advantage of the simple machines.
• Test under load, not just voltage. A battery can read 12.6V at rest and still collapse when the starter engages. If your standby cranks slowly, replace the battery — don’t wait for the no-start.
• Keep terminals clean. Corrosion = resistance = slow cranking = no start on the coldest night of the year.

Fuel System Care

• Rotate gasoline stock every 6–12 months (pour old gas into your car — it’s fine).
• Inspect fuel lines annually for cracking, especially on older portables. Ethanol-blended gas is harder on rubber lines and carburetor components.
• Replace the inline fuel filter (if equipped) annually.
• For propane units: check regulator and hose connections for leaks with soapy water, never a flame. Sniff-test around tanks monthly — propane has odorant added specifically so you can detect it.

DIY vs Call a Tech

Comfortable DIY: oil and filter changes, air filter, spark plugs, battery replacement and terminal cleaning, fuel stabilizer, monthly test runs, visual inspections, keeping the area clear.

Call a tech for: valve lash adjustment, transfer switch diagnosis or repair, anything involving the natural gas or propane supply line, controller fault codes you can’t clear, warranty-period service (DIY during warranty can void it — read your terms).

A professional annual service visit for a standby typically runs $250–$400. Given a $10,000+ installed standby, that’s reasonable — and many dealers offer service plans that include priority response during outages.

Pre-Storm Checklist

When a storm is 48 hours out, run this:

• Start the generator and run it 15 minutes under load — confirm it starts, runs smooth, and makes power
• Check oil level; top off if needed
• Fuel: full tank on the portable + reserve cans filled (stabilized); propane tank above 50% for standby
• Starting battery: terminals clean, cranks strong (standby: no fault codes on controller)
• Extension cords / transfer switch: cords untangled and rated for the load, interlock or transfer switch accessible
• Generator positioned: 20+ feet from house, exhaust away, on dry ground, cable-locked
• CO detectors in the house: test the batteries
• Phone numbers saved: your generator tech, propane dealer, utility outage line

Printable Summary

Standby — yearly cycle:

• Weekly: automatic exercise (verify monthly it’s happening, check for fault codes)
• Monthly: visual inspection, clearance, propane gauge
• Annually: oil + filter, air filter, spark plugs, transfer-switch test
• Every 3–5 years: battery replacement; every 2–3 years: valve adjustment (tech)

Portable — yearly cycle:

• Monthly: start and run 15 min under load
• Every 50–100 hours or annually: oil change
• Storage: stabilizer + run-through, or run the carb dry
• Every 3–5 years: starting battery (electric-start models)

Both: keep fuel fresh and stored safely, keep the unit clean and clear, test before storm season — not during it.

A generator’s lifespan is directly tied to this schedule. A maintained standby runs 20–30 years; a neglected one dies at 8. For the full picture on how long each type lasts and what kills them early, see our generator lifespan guide, and for the broader backup-power decision, the pillar: home backup power explained.