Generator Maintenance: Cost, Hours and Process in Hacienda Heights

Onan specifies service by running hours. A typical air cooled gas unit wants oil and filter at 150 hours and a valve lash check at 500. A diesel unit runs a different schedule. None of those numbers correspond to a calendar, which is why a coach that is used twice a year can still be badly overdue and a coach used constantly can be current.

The hour meter is on the unit or in the coach control panel, and reading it is the first thing we do. Owners are frequently surprised, either direction. A snowbird who runs the generator on the road all summer accumulates hours fast. A weekend owner on shore power at a park may add ten hours a year.

The other trap is that the calendar does matter for one thing: fuel. Gasoline in a generator that sits for a year gums a carburetor, and that is the single most common reason a healthy generator will not start. Running the unit monthly under load is the cheapest maintenance there is and it costs nothing but attention.

• Oil and filter, by hours on the meter rather than by season
• Air filter, which loads faster in valley summer dust than the interval assumes
• Spark plugs on a gas unit, fuel filter and water separator on a diesel
• Valve lash check at the specified hour interval
• Fuel system inspection for varnish and gummed passages
• Load test at real demand rather than a no load run

A generator that starts and idles has proven almost nothing. Nearly every generator will idle. The question is whether it holds voltage and frequency with two air conditioners, a water heater element and a microwave asking for current at once, because that is the only condition where the coach needs it.

So the service ends with a load test. We put real load on the unit and watch voltage, frequency and behavior as it comes up and as loads step on. A unit that sags, hunts or drops out under load has a fuel delivery, governor or winding problem that a no load run would never have exposed.

That is also why exercising the generator monthly matters, and why exercising it at no load is nearly pointless. Running under load keeps the fuel system wet, brings the unit to temperature, burns off moisture in the crankcase and loads the windings. Twenty minutes with the air conditioning on beats two hours at idle.

The band on this page is narrow because the scope is defined. Labor runs at the posted mechanical and electrical rate of $260 per hour across 2 to 6 hours, plus parts. A gas unit oil, filter, air filter and plug service with a load test is near the bottom. A diesel unit with a valve lash check and a fuel system service is toward the top.

The estimate tier here is the RV systems estimate at $150, credited against an authorized repair. If the load test reveals a fault, that becomes a repair conversation on the generator repair and overhaul page rather than being absorbed into a maintenance line item, because the two are billed differently and we would rather you see them separately.

One boundary to name clearly. This is the house generator, which is the Onan or Cummins unit in the coach bay. The chassis engine that moves the vehicle is a different machine and this facility does not work on it. That distinction is stated on every generator page here because a lot of shops blur it.