RV Generator Maintenance Checklist: The Service That Prevents a No-Start

An RV generator is the only major appliance in your rig that punishes you for not using it. Fridges, furnaces, and water heaters sit idle without complaint. A generator that sits idle gums up its carburetor, dries out its seals, and greets you with a starter that spins and spins on the first 90-degree afternoon you actually need the air conditioning.

This is the seasonal service for the onboard gas generators most owners have — Cummins Onan QG 2500/4000, Generac, and the Champion and Firman units on newer trailers. It's built around the hour meter, not the calendar, because that's how these engines are actually rated. Budget an hour, a quart or two of oil, and a drain pan. I'll flag the two or three steps where the honest answer is "let a tech do this."

Run it by the hour meter, not by the season

Find your hour meter first — on Onan units it's on the control panel or read through the remote start switch by holding the stop side for a few seconds. Every interval below is engine hours, and if you can't find a manual for your exact model, these are the conservative defaults:

• Oil and oil filter — every 100–150 hours, or once a year. Onan QG gas units spec 150 hours; the first change after a new or rebuilt engine comes early, around 20–50 hours.
• Air filter — inspect every 50 hours, replace every 150–200. Sooner if you boondock on dirt.
• Spark plug — every 250–500 hours. Gap matters; a worn plug shows up as hard starting under load.
• Spark arrestor — clean every 50–150 hours. A clogged one chokes power and is a genuine fire risk in dry country.
• Fuel filter — annually on units that have a serviceable one.

Write the hours and the date on a strip of tape inside the generator door. Two seasons from now you will not remember.

The monthly exercise run — the single best habit

More generators die of neglect than of wear. Once a month, run yours for at least two hours under real load — not a five-minute idle. Load means turn on an air conditioner, or the AC plus the microwave or a space heater; somewhere around half the unit's rated output is the goal.

Two hours under load does three things a short idle can't:

1. Gets the engine to full operating temperature, which boils off the water and raw fuel that condense in the crankcase and turn oil into acid.
2. Pulls fresh fuel through the entire carburetor, so the tiny main jet and pilot passages don't varnish shut. A varnished carb is the number-one reason a stored generator won't start.
3. Carbon-cleans the cylinder and exhaust instead of glazing them with the soot a lightly-loaded engine makes.

If yours has sat all winter, that first run may need a few cranking cycles (10–15 seconds at a time, 30 seconds of rest between so you don't cook the starter) while fuel refills a dry bowl.

Fuel, and the quarter-tank rule that surprises people

Most motorhome generators draw from the same gas tank as the chassis engine, but the generator's pickup tube stops around the 1/4 mark — deliberately, so you can't strand yourself without engine fuel. If your generator quits or won't start and the gauge reads a quarter tank or less, you may not have a generator problem at all. Add fuel before you troubleshoot anything else.

On stored rigs, the fuel itself is the enemy. Pump gas with ethanol starts degrading in about 30 days and attracts water. Before any storage longer than a month, add a stabilizer at the label dose and then run the generator 10–15 minutes so treated fuel actually reaches the carburetor — stabilizer sitting in the tank while the bowl holds untreated gas does nothing for the part that clogs.

The physical walk-around

With the generator off, cool, and the shore power disconnected:

• Check oil on level ground, with the correct grade for your season (many gas RV generators want SAE 30 above 32°F, 5W-30 below). Overfilling is as bad as running low — it foams and blows past seals.
• Pull the air filter and look at it in the light. Foam elements can be washed and lightly re-oiled; paper elements get replaced, never washed.
• Clean the spark arrestor screen. Remove it, burn or brush off the carbon, and reinstall. Clogged screens rob power and throw sparks.
• Inspect the exhaust from the engine to the tailpipe. Look for soot streaks at joints, rust holes, loose clamps, and a tailpipe that still extends past the sidewall. An exhaust leak under a coach is a carbon monoxide problem, not a noise problem — stop and get it fixed.
• Test the CO detector while you're at it. Press the button, and check the date: RV CO detectors expire, usually 5–7 years from manufacture.
• Check the mounts and wiring. Vibration loosens mount bolts and chafes harness insulation against the slide tray. Look for shiny bare copper.
• Clear the cooling intake and the compartment. Mud-dauber nests and mouse bedding in a generator compartment are common, and both cause overheat shutdowns.

Reading the shutdowns your generator is trying to tell you about

Modern units shut themselves down and blink a fault code rather than self-destruct. Learn the three common ones:

• Low oil pressure shutdown — usually genuinely low oil, or oil so thinned by fuel dilution it can't hold pressure. Check the level before you blame the sensor.
• Overheat / high temperature — blocked intake, packed compartment, or a failing cooling fan.
• Overload — you asked two air conditioners of a one-air-conditioner generator, or a shorted appliance. Shed load and reset before assuming the generator failed.

A unit that starts, runs 10–20 seconds, and dies is nearly always a fuel- delivery story: a varnished carburetor, a stuck float, or a failed fuel pump.

When to call a pro

Oil, filters, plugs, the arrestor, and the exercise run are owner-level work. Bring in a technician when:

• It cranks but never fires after fresh fuel and a good plug — that's carb or fuel-pump territory, and the carb usually needs removal and cleaning.
• It starts but won't hold load, surges, or drops voltage under an AC.
• There's any exhaust leak, soot inside a compartment, or CO alarm. Stop using it until it's inspected.
• The automatic transfer switch doesn't hand over from shore power — that's 120V wiring, and it's a real shock and fire risk. It belongs with RV electrical repair, not a weekend fix.
• It's burning oil, smoking, or leaking from the case.

A dead generator is the kind of failure that strands you where the shops aren't. Mobile techs come to the rig — whether you're plugged in at a park in Phoenix or need RV generator repair in Denver before a mountain trip. Every system and city we cover is on the RV repair hub.

FAQ

How often should I run my RV generator if I'm not camping? Once a month, two hours under real load — an air conditioner is the easiest load to apply. That single habit prevents most storage-related no-starts.

Why won't my generator start when the fuel gauge shows fuel? Check whether you're under a quarter tank. The generator pickup tube ends higher than the engine's so you can't drain the tank running it, so a quarter-tank reading can mean the generator is already dry.

Can I use car oil in an RV generator? Yes, if it matches the grade and API service class in your manual — most gas RV generators run standard SAE 30 or 5W-30. Match the viscosity to the temperature you'll actually be running in, and change it on hours, not miles.

Is a generator that only runs one air conditioner defective? No. A 3,600–4,000-watt unit is a one-AC generator once you count the converter, fridge, and outlets. Running two rooftop units generally needs 5,500 watts or more, plus soft-start capacitors — see our RV air conditioner maintenance checklist for keeping that load as low as possible.

One call if it still won't start

Do the hour-meter service and the monthly load run, and your generator will start when the temperature says you need it. If it cranks and won't catch anyway, don't spend a trip on it — call 833-FIXED-RV (1-833-349-3378). One call, answered live 24/7, and we connect you to a vetted, licensed, insured local pro who can diagnose the fuel system on site. Every job is backed by our $2,500 Workmanship Guarantee, so it's done right or we make it right.