Scheduled Generator Service on the Hour Meter
Written by RV Systems Lead, RV Systems and Electrical Lead, OCRV Center. Reviewed by Fleet Account Manager
In shortRV gensets die from light loading and stale fuel, not from hours. A service visit covering oil, filters, plugs and a loaded run costs $400 to $1,800.
What does scheduled generator service include on an RV?
Scheduled generator service covers oil and filter, air and fuel filtration, spark plugs on gasoline sets, valve lash at interval, spark arrestor cleaning and a loaded run test. Owners from Rancho Santa Margarita book these visits at our Yorba Linda facility on the hour meter rather than by calendar guesswork.
- Oil and filter every 150 hours or annually, whichever comes first
- Valve lash gets checked at interval, not when something sounds wrong
- A genset needs a loaded exercise run every month
- Fuel left through a storage season is the leading no start cause
- Price range
- $400 to $1,8002 to 7 labor hours at $260 per hour
- Labor rate
- $260 per hourMechanical and electrical department
- Typical turnaround
- 1 to 2 shop daysSame visit where the set is accessible and parts are stocked
- Written estimate
- $150Credited in full against an authorized repair
- Disposal
- $45 flatApplies where oil, coolant or LP handling is involved
Last verified
The hour meter on an RV generator tells a story most owners never read. A set with three hundred hours that has spent all of them running a single roof air on a hot afternoon is in worse shape than one with six hundred hours behind a real load, and the maintenance both of them need is scheduled off that meter rather than off a calendar.
What brings most sets into our bays is not wear. It is neglect of two specific kinds: fuel that sat through a long storage season and turned to varnish, and years of running at a fraction of rated output so the engine never got hot enough to clear its own carbon. Both are preventable on a schedule.
The intervals that actually keep a set alive
Small air cooled engines live a harder life than the chassis engine sitting a few feet away. They run at a fixed high speed, they cool themselves with air rather than a liquid loop, and they sit in a compartment where ambient temperature is already elevated. Oil in that environment shears down quickly, which is why the interval is measured in the low hundreds of hours rather than in thousands of miles.
The intervals that get skipped are the ones that require tools rather than a drain pan. Air and fuel filtration usually happen. Valve lash and spark arrestor cleaning usually do not, and both of them protect the parts that are expensive to fix. A set that has had its oil changed religiously and its lash never checked is not a well maintained set.
| Item | Interval | Consequence of skipping |
|---|---|---|
| Oil and filter | 150 hours or annually | Additive package sheared, accelerated bore wear |
| Air filter element | Annually or after dusty use | Rich mixture, carbon on valves and rings |
| Spark plugs, gasoline sets | Around 450 hours | Hard starting, misfire under load |
| Valve lash | Around 500 hours | Lost compression, eventually a burned valve |
| Spark arrestor screen | Annually | Exhaust restriction, heat and power loss |
Under loading is what kills most RV generators
These engines are designed to carry real output. Combustion temperature at a meaningful load is high enough to keep the combustion chamber, the valves and the exhaust path reasonably clean. Run the same engine at a tenth of its rating and combustion stays cool, unburnt fuel finds its way past the rings, plugs foul and the exhaust system fills with soft carbon that eventually restricts flow.
The advice we give is unglamorous and it works. Once a month, start the set and put it under at least half its rating for two hours. On a coach that means both roof air units and the water heater element together, not a phone charger. Owners who adopt that routine stop seeing us for fouling complaints entirely, and their sets keep making rated output well past the hour count where neglected ones start to fade.
Note
Half rated output for two hours a month is the single most effective thing an owner can do for a generator. It costs a few gallons of fuel and it prevents most of the failure modes on this page.
Fuel that sat through a storage season
Modern pump gasoline is not a storage fluid. The light fractions evaporate, what remains oxidizes, and the ethanol component attracts water out of the air. In a vented carburetor bowl that process leaves a lacquer film that blocks the idle circuit first and the main jet shortly after. The set cranks perfectly, has good spark, and simply will not run.
Diesel sets fail differently and just as reliably. Microbial growth at the fuel and water interface in a tank that sat half full produces a sludge that plugs filters within minutes of the set starting. The symptom is a unit that fires, runs briefly and shuts down as the filter loads up, which owners often mistake for an electrical fault.
- Gasoline sets: varnish in the bowl blocks the idle circuit first
- Diesel sets: microbial sludge plugs the filter within minutes of starting
- A stabilizer added before storage prevents both, added afterward prevents neither
- Running the set monthly moves fresh fuel through the whole path
Valve lash, plugs and the interval nobody books
Valve clearance changes over time as the seats wear and the valve sinks slightly into the head. As lash closes up the valve is held open marginally longer than intended, compression falls, and eventually the valve cannot transfer heat into the seat properly and burns. Everything about that sequence is preventable with a feeler gauge and an hour of access, which is why it appears on the interval table at all.
Plugs are the other honest witness. We read them rather than binning them, because a plug tells you about the mixture, the oil control and the way the set has been used. A light tan insulator on a set with four hundred hours says the owner has been loading it properly. Black and wet says the opposite, and it changes what else we look at during the visit.
What comes off and gets checked on a service
Access shapes the visit more than anything else. On a Class C where the set sits behind a hinged door with room to work, the whole scope is straightforward. On a diesel pusher where the set lives on a slide out tray, pulling that tray out and back is a real part of the labor and it goes in the estimate as such rather than being absorbed silently.
Everything we remove gets read before it is discarded. Filter loading, plug colour, oil condition and the state of the arrestor screen together describe how the set has actually been used, which is usually more informative than the service record. That reading is what determines whether the next visit needs a broader scope.
- Confirm hours and previous documented service
- Cold start and listen before anything comes apart
- Replace consumables and read each item as it comes off
- Measure valve lash and clear the spark arrestor
- Run under load and record voltage and frequency
What scheduled generator service costs
Service bills through the mechanical and electrical department at $260 per hour across a two to seven hour range. The bottom of that range is a straightforward consumables visit on an accessible set. The top is a full interval service including valve lash, a carburetor clean after a storage season, and the tray work required to reach a set mounted in a slide out compartment.
Parts carry standard markup and tax applies to parts and materials. Every visit involving oil, coolant or LP handling carries the flat hazmat and disposal charge of $45. A written repair estimate is $150 and comes back in full against an authorized repair, which matters when a service visit turns up something that needs a larger conversation.
On cost
If a service uncovers a compression or output problem, we stop and quote that separately. Maintenance and repair are different jobs and combining them into one number helps nobody.
Sets we see week to week
Cummins Onan RV QG gasoline sets dominate the motorhome side of our schedule, with Marquis and Marquis Gold units still common on coaches from the previous two decades. Diesel pushers bring QD sets on slide trays, which change the labor picture considerably even though the service items themselves are familiar.
The commercial side skews differently. Food trucks and command units run their sets far harder and far longer than any personal coach, which brings them onto a much tighter interval and makes the loaded run test a genuine acceptance check rather than a formality.
What is included
- Oil and filter replacement with the correct grade
- Air cooled sets run hot and are unforgiving about oil specification, so the grade goes in per the manufacturer rather than per what is on the shelf.
- Air and fuel filtration service
- Elements are replaced, housings are checked for a proper seal, and inline fuel filters on diesel sets are changed with the system primed afterward.
- Ignition service on gasoline sets
- Plugs are replaced at the correct heat range and gap, and the condition of the old ones is read as diagnostic information rather than discarded.
- Valve lash inspection at interval
- Lash is measured cold against specification and adjusted where it has drifted, which protects compression before a valve gets burned.
- Exhaust and spark arrestor cleaning
- The arrestor screen is removed and cleared, and exhaust gaskets and hangers are inspected while access is open.
- Loaded run test with output verified
- The set runs against a real load while voltage and frequency are recorded, since an unloaded run proves very little.
How the work runs
Read the meter and the history
30 minutes
Hours, the last documented service and how the coach is actually used all shape the scope. A rental unit running heavy loads weekly and a personal coach that idles a generator twice a year need different work at the same hour reading.
Start it cold and listen
30 minutes
How a set behaves on a cold start tells us about fuel delivery, compression and ignition before anything is opened. Surging, hard starting and a shutdown after two minutes each point somewhere specific, and starting warm hides all three.
Service the consumables
1 to 3 hours
Oil and filter, air element, fuel filtration and plugs come next, with the old parts read rather than binned. Plug colour, filter loading and oil condition together describe how the set has been used far more honestly than any owner recollection.
Check lash and clear the exhaust
1 to 2 hours
Valve clearance is measured cold at interval and adjusted where needed, and the spark arrestor screen is pulled and cleared. Both are skipped by most quick service routines and both directly affect whether the set makes its rating.
Run it under load and record output
1 hour
The set carries a genuine load while voltage and frequency are measured and written down. Those numbers become the baseline for the next visit, which is what turns a service history into something useful.
What this costs
$400 to $1,800
2 to 7 labor hours at $260 per hour, mechanical and electrical.
- Hazmat and disposal $45 flat when chemicals, refrigerant or LP is involved.
- Parts at $100 or less carry 100 percent markup. Parts over $100 carry 35 percent. Special order parts require a full non refundable deposit at order.
- Sales tax of 7.75 percent applies to parts and materials. Labor is not taxed.
- A straightforward oil, filter and plug service on an accessible set sits at the bottom of this range.
- A full interval service with valve lash, carburetor cleaning and a slide tray pull sits at the top.
- Oil disposal carries the flat hazmat charge of $45 on every visit involving fluids.
How estimating is billed
- Written repair estimate: $150, credited in full against an authorized repair.
- In depth diagnostic, scan and programming: $285 per hour, one hour minimum, credited in full against an authorized repair.
- In shop pre purchase inspection: $400 to $1,200 depending on unit size and systems count.
- Insurance walk ins are accepted during posted hours. All inspection and estimating work is performed in shop at the Yorba Linda facility.
What you will notice first
- The set cranks strongly and will not fire after a winter of storage
- It starts, runs for two minutes and shuts down on its own
- Black soot around the exhaust outlet and on the paint below it
- Output drops when the second air conditioner cycles on
- A surging note in the exhaust that rises and falls once a second
- Oil on the dipstick that is black and thin after a single season
- Hard starting that needs several attempts where it used to catch immediately
- A rattle from the valve cover area that was not there last year
How this fails, and what we do about it
| Failure mode | How we diagnose it | The fix |
|---|---|---|
| Varnished carburetor after storage | Strong cranking, good spark, and no fuel reaching the cylinder. Pulling the bowl reveals a lacquer film and often a green tint in the residue. The idle circuit blocks before the main jet does, which is why some sets fire briefly on starting fluid and then quit. | Remove and bench clean the carburetor with a full kit, then run the set under load to confirm it holds. Chemical treatment poured in the tank does not reach a jet that is already blocked. |
| Carbon loading from light duty running | Black soot at the exhaust, a spark arrestor packed solid and plugs fouled well before their interval. Compression is usually still acceptable at this stage, which distinguishes it from genuine engine wear. | Decarbonize, replace plugs and the arrestor screen, then set the owner up with a monthly loaded exercise routine. Without that routine the same condition returns within a year. |
| Valve lash out of specification | A light rattle at the head, reduced power under load and a compression reading below where it should be for the hours. Measuring lash cold with feeler gauges confirms it, and the intake side is usually the one that has closed up. | Adjust to specification with the engine cold. If a seat has receded far enough that adjustment brings the valve close to its limit, the head goes on the list for a closer look. |
| Restricted air path | A filter grey with dust, a richer than normal exhaust note and a set that makes rated output for a few minutes then falls off. Common on coaches that have spent seasons on desert roads or parked near construction. | Replace the element rather than blowing it out, and check the housing seal. A filter cleaned with compressed air passes particles that will find the cylinder wall. |
Why it happened
- Ethanol blended gasoline left in a carburetor bowl through storage, which evaporates into varnish and blocks the main jet and the idle circuit
- Chronic light loading, where a set rated for several thousand watts spends its life carrying a few hundred and never reaches operating temperature long enough to burn off deposits
- Oil left beyond its interval in a small air cooled engine that runs hot by design and shears the additive package quickly
- An air filter clogged by desert dust after a season of dry camping, which richens the mixture and accelerates carbon build up on valves and rings
- Valve lash drifting out of specification as the seats wear, which reduces compression and eventually holds a valve open enough to burn it
- A spark arrestor screen packed with carbon, which restricts exhaust flow and produces heat and power loss that get blamed on the engine
Parts and brands we work with
- Cummins Onan RV QG gasoline sets in 2800, 4000 and 5500 watt ratings
- Onan Marquis and Marquis Gold sets on older Class A and Class C coaches
- Cummins Onan QD diesel sets on diesel pusher chassis
- Genuine Onan oil, air and fuel filters plus the correct plug heat range
- Fuel stabilizer and carburetor service kits for seasonal storage work
- Spark arrestor screens and exhaust gaskets replaced at service intervals
What not to try yourself
- Storing a coach with untreated gasoline in the generator fuel path. Varnish forms in the bowl and the jets over a single season and no additive poured in later will dissolve it.
- Running a set with no load for twenty minutes and calling it exercise. Light running is what causes the carbon problem, so an unloaded run makes the situation worse rather than better.
- Cleaning an air filter element with compressed air and reinstalling it. The blast opens paths through the media that pass exactly the particles the filter existed to catch.
- Ignoring a surging note because the set still produces power. Surging means the fuel system cannot hold a stable mixture, and the condition behind it does not stay stable either.
Which vehicles we do this on
Vehicles we perform Generator Maintenance on
Class A GasClass A gas motorhome repair covers the molded front and rear caps, the vacuum bonded laminated sidewalls, the EPDM roof and the F53 chassis underneathClass CClass C motorhome repair centers on the cabover bunk, the joint where the coach body meets the factory van cab, and the stick built or laminated house behind itDiesel PusherDiesel pusher repair means working on a rear engine coach built on a welded Freightliner XC or Spartan rail, with a full body painted fiberglass shell and large basement baysToy HaulerToy hauler fifth wheel repair concentrates on the ramp door hinge line at the rear wall, garage floor deflection between crossmembers, and sag in the frame cantilevered behind the axlesFood TruckFood truck repair covers the step van body, the serving window aperture and its header, the roof hood curb, the coved floor under the cooking line and the generator compartmentCommand CenterMobile command center repair covers the telescoping mast base and its roof penetration, satellite and antenna curbs, the conference slide opening, equipment rack floor mounts and the diesel generator compartmentI ask every owner the same question before I touch the set: when did you last run it against a real load. Most people say they start it monthly and let it idle for fifteen minutes, and they think they are doing the right thing. That habit is precisely what fouls plugs and packs an arrestor screen solid. Two hours a month with both air conditioners running does more good than a year of unloaded idling, and it costs nothing but fuel.
Appendix: questions and answers
- How often does an RV generator need an oil change?
- Around every 150 hours or annually, whichever arrives first. These are air cooled engines running at fixed high speed inside a warm compartment, so the oil shears down considerably faster than chassis engine oil does. The calendar half of that rule matters as much as the hour meter half.
- What is the right way to exercise a generator that sits unused?
- Run it at half its rating or better for about two hours each month. On a motorhome that means both roof air units and the water heater element together. Idling a set with no load for fifteen minutes is worse than not running it, because light loading is what fouls plugs and packs the arrestor.
- My generator cranks but will not start after winter storage. Why?
- On a gasoline set, almost always varnish in the carburetor. Fuel left through a season evaporates and leaves lacquer that blocks the idle circuit and then the main jet. Cleaning requires removing the carburetor and going through it with a kit, since additives cannot reach an already blocked passage.
- Is valve lash adjustment really necessary on a small generator?
- Yes, and it is the interval most often skipped. As seats wear the clearance closes, compression falls and eventually a valve cannot shed heat into its seat and burns. An hour with feeler gauges at the specified interval prevents a head repair that costs many times more.
- What does black soot around my generator exhaust indicate?
- Incomplete combustion, usually from chronic light loading or a restricted air filter. The set has been running too cool to burn fuel completely, so carbon is accumulating in the chamber and the exhaust path. Decarbonizing plus a proper loading routine resolves it, and skipping the routine brings it straight back.
- Does a slide out generator tray add much to a service visit?
- It adds real hours. Extending and securing the tray, working around the service loop and returning everything correctly is genuine labor rather than a formality, particularly on a diesel pusher. We put that time in the estimate openly instead of hiding it inside a flat service price.
Open a file on this repair
Tell us the vehicle, what happened and whether a claim is open. We will tell you what the scope looks like and what it takes to get you back on the road.
Or call (949) 799-3387