Onan RV generators: what fails in Florida and what repairs cost

Onan is what is mounted in most motorhomes and a good many fifth wheels, and in Florida it fails in one dominant way: it sits. The seasonal use pattern here, run through the winter season from November to April and then parked from spring to fall in humid heat with fuel in the system, is close to the worst thing you can do to a small gasoline engine. Almost every November and December generator call we take traces back to it.

The fuel problem, in detail

Modern pump gasoline is not a storage fluid, and ethanol gasoline in Florida is worse than most places. Ethanol is hygroscopic: it pulls water out of the air. In a carburetor bowl vented to air that sits above 90 percent relative humidity every night from May to October, the fuel takes on water until the ethanol and water drop out of the gasoline as a separate layer at the bottom of the bowl. That layer sits on the main jet. Above it, the light fractions of the gasoline evaporate and leave a varnish that sets in the passages. Those passages are measured in thousandths of an inch.

The water layer also corrodes the aluminum of the bowl and the jets from the inside, which is why a carburetor from a Florida rig often needs replacing rather than cleaning where a desert one would clean up.

The result is a generator that cranks fine and will not fire, or fires and dies, or runs and surges. All three are the same underlying fault and all three are fixed the same way: the carburetor comes off, gets cleaned or replaced, and the fuel system gets checked back to the tank.

What things cost

Same approach as everything on our pricing page: diagnose, quote, get your approval, then work.

The failure order on these units

1. Fuel system, by a wide margin, for the reasons above.
2. Corrosion on connectors and grounds. The generator’s control wiring and the remote start harness live in a compartment that is damp for half the year. Green connectors and a poor chassis ground produce start faults, fault codes, and no-output complaints that have nothing wrong with the engine or the windings.
3. Plugs and air filters, neglected because the generator is out of sight. A paper air filter that has spent a summer in humid air is soft and partly collapsed.
4. Oil, which on a generator is measured in running hours and is routinely never changed at all. Generator hour meters exist for a reason.
5. No AC output with the engine running happily. This is the electrical side: brushes, capacitor, voltage regulator, or a tripped breaker on the unit itself. The voltage regulator is a circuit board, and a nearby lightning strike can take it while the generator is sitting idle in the bay. The good news is that it means the engine is fine.
6. Starting and control faults, including the remote start panel and its wiring.
7. Exhaust, which is a safety item rather than a performance one and is covered below. Exhaust systems rust faster here than anywhere dry.

The habit that prevents nearly all of it

Run it for two hours a month under load. Not at idle, not for five minutes. Under load, meaning with an air conditioner running, long enough to get everything hot.

Owners who do this essentially never call us about a generator that will not start. It keeps fresh fuel moving through the bowl, burns off the moisture, circulates oil, dries the windings, and exercises the start circuit. It is free, it takes no skill, and it is the most effective maintenance advice on this entire site.

If the rig genuinely has to sit from April to November while you are north, the next best options are treating the fuel with a stabilizer that is made for ethanol and running it through, or shutting off the fuel and running the bowl dry where the unit allows it. Running the bowl dry is the better answer here, because a dry bowl cannot take on water.

Heat, humidity, and honest expectations

Generators are rated under standard conditions, and output falls as temperature and humidity rise, because moist hot air carries less oxygen per cubic foot than cool dry air. On a 90-degree August afternoon in Zephyrhills with the dew point in the 70s your unit is not making its nameplate number. If it has always struggled to carry two rooftop air conditioners in summer, that may be physics rather than a fault, and we will say so instead of selling you a rebuild.

The practical fixes for that are cheap: stagger the AC starts rather than letting both compressors hit at once, and consider soft-start devices on the air conditioners, which dramatically cut inrush current. Many “my generator cannot handle my rig” complaints are solved for a fraction of any repair.

The safety paragraph

Two things we will always raise:

Exhaust integrity. A leaking generator exhaust on a motorhome is a carbon monoxide risk, and these systems rust through in a humid climate well before the engine is tired. If we find one, we will tell you and we will recommend not running the unit until it is repaired.

Your CO alarm. Check that it works and check its expiry date, because they do expire. That is free advice and it is the most important sentence on this page.

The generator repair service page covers the full scope of what we do on site, across Zephyrhills, Dade City, Wesley Chapel, San Antonio, Land O’ Lakes, Lutz, and Plant City. If you are arriving in November to a generator that sat since April, the arrival checklist is worth ten minutes before you press the start button.