Generator Maintenance: Protecting Your Wisconsin Home Before Storm Season

If you own a standby generator in Wisconsin, you probably bought it after losing power during a storm and swearing you'd never deal with that again. Maybe it was the 2022 Christmas blizzard, or one of those summer derechos that knocked out power across Sheboygan County for days. Whatever the reason, your generator was an investment — and like any mechanical investment, it only works when you need it if you maintain it when you don't.

I've installed and serviced generators across SE Wisconsin for years. The most frustrating call I get is from a homeowner whose generator didn't start during an outage because of something a basic annual service would have caught. Here's the maintenance checklist I walk through with every customer.

Oil and Filter: The Non-Negotiable

Standby generators run on internal combustion engines — the same basic technology as your car. The oil needs changing at regular intervals, and in Wisconsin's climate, the interval matters more than you'd think. Most manufacturer guidelines call for an oil change every 200 hours of run time or once a year, whichever comes first. But here's the thing: even if your generator only ran for 8 total hours last year, that oil sat in a cold engine through months of sub-zero temperatures, then heated up during weekly exercise cycles, then went cold again. That thermal cycling degrades oil faster than the hour meter suggests.

Use the oil weight specified by your generator's manufacturer — typically 5W-30 for Wisconsin year-round operation on air-cooled units (Generac, Briggs & Stratton) or the OEM-recommended synthetic for liquid-cooled units (Kohler, Generac Protector series). Change the oil filter at every oil change, no exceptions. A $12 filter is cheap insurance.

Battery: The Number One Failure Point

The generator battery is the single most common reason generators fail to start during an outage. The engine can be perfect, the fuel system clean, the transfer switch ready — and a dead battery means nothing happens when the power goes out. Standby generator batteries are smaller than car batteries and live outdoors (or in an unheated enclosure) through Wisconsin winters. That's extraordinarily hard on a lead-acid battery.

Check the battery voltage with a multimeter. A fully charged 12V battery should read 12.6-12.8 volts. Anything below 12.4 volts means it's partially discharged and may not have enough cranking power in cold weather. Below 12.0 volts, replace it. Also check the terminals for corrosion — that white/green crud that builds up on battery posts — and clean them with a wire brush and anti-corrosion spray. Most generator batteries last 3-4 years in Wisconsin. If yours is older than that, replace it preemptively. A new battery costs $80-150. A failed start during a winter ice storm costs you a lot more.

Coolant System (Liquid-Cooled Units)

If you have a liquid-cooled standby generator (typically 20kW and larger), the coolant needs the same attention it would in a vehicle. Check the coolant level and condition. It should be the proper color for the type (usually pink or green) and free of rust particles or oil contamination. Wisconsin's freeze-thaw cycles make proper coolant concentration critical — test with an antifreeze hydrometer and confirm it's good to at least -30F. We've seen -20F-plus in Sheboygan County more than once in recent years, and a frozen coolant system will crack the block.

Replace the coolant every 2-3 years or per the manufacturer's schedule. And check the hoses for cracking, bulging, or soft spots while you're at it.

Transfer Switch Inspection

The automatic transfer switch (ATS) is the brain of your backup power system. It monitors utility power, detects an outage, signals the generator to start, and transfers your home's load from the utility to the generator — all in about 10-30 seconds. When utility power returns, it transfers back and shuts down the generator.

Transfer switches contain relays and contactors that can corrode, pit, or stick over time. An annual inspection should include checking the contacts for pitting or carbon buildup, verifying the control board is functioning (most have diagnostic LEDs), and testing the automatic transfer sequence. This isn't a DIY job — transfer switches carry full household voltage and amperage. Have your electrician include it in the annual service. For more on generator systems and what's involved, see the generator installation guide.

Exercise Schedule: Use It or Lose It

Every standby generator has a built-in exercise cycle — a programmed weekly run, typically 10-20 minutes, that keeps the engine lubricated, charges the battery, and cycles the fuel. Make sure yours is actually running. I can't count the number of times I've arrived at a service call to find the exercise cycle was accidentally turned off, the run time was set to 3 AM on a day nobody's home to hear it fail, or the utility power was interrupted during an exercise cycle and confused the controller.

Set the exercise cycle to a time when someone is home and awake — Saturday morning at 10 AM works for most people. Listen for it. If it doesn't run, or if it starts and shuts down after a few seconds, that's an early warning of a problem. Running under load during exercise (if your unit supports it) is even better — it prevents wet-stacking (unburned fuel residue in the exhaust) and tests the system more thoroughly.

Fuel System: Natural Gas, Propane, or Diesel

Most standby generators in our service area run on natural gas or propane.

• Natural gas: Minimal fuel-side maintenance — the supply is continuous from the utility. But check the gas line connections for leaks annually (soapy water on every fitting, look for bubbles) and make sure the gas shutoff valve operates freely.
• Propane: Common in rural Sheboygan County where natural gas isn't available. Check your tank level before storm season. A 500-gallon tank powering a 20kW generator under moderate load burns roughly 2-3 gallons per hour. A 72-hour outage — not unusual after a major ice storm — uses 150-200+ gallons. Fill the tank in early spring when propane prices are lower.
• Diesel: Less common for residential but used on some larger installations. Diesel degrades over time — fuel sitting for more than 6-12 months develops algae, water contamination, and varnish. Use a fuel stabilizer and consider having the tank drained and refilled annually if the generator runs infrequently.

Air Filter and Spark Plugs

Check the air filter at every service. A clogged air filter makes the engine run rich, wastes fuel, and can cause hard starting. In rural Wisconsin, pollen, dust from agricultural fields, and cottonwood fluff can pack a filter tight in a single season. Inspect spark plugs on gasoline and propane units — they should be clean and properly gapped. Replace per the manufacturer's schedule, usually every 200-400 hours or every 2 years.

Schedule Your Service Before Storm Season

The best time to service your generator is late winter or early spring — right now. Don't wait until the tornado sirens test in April or the first severe thunderstorm watch of the season. Electricians and generator techs get slammed with calls after the first outage of the year, and by then you're competing with everyone else who also forgot. A comprehensive inspection and annual generator service takes 1-2 hours and gives you confidence that when the lights go out, yours will come back on.