Understanding the inner workings of a motorhome generator and how it should be maintained can save time, money and trouble
If you’ve ever endured a blackout, you understand how easy it is to take reliable, accessible power for granted. You stumble around lighting candles, and even after hours of living in relative darkness, you still find yourself reaching for light switches in vain. Though frustrating, you know the electric company will fix the problem and life will eventually return to normal — but in a motorhome, it may not be that easy. While it’s true that the 12-volt DC system will keep your lights on (for a while), other modern conveniences that run on 120-volt AC power (like the TV, air conditioner, microwave and other appliances you may bring) won’t be available if the generator goes down when you’re boondocking. Your best defense against such a scenario is regular generator maintenance.
Most of us wouldn’t think of buying a car, driving it a few miles each summer, and then ignoring it for the rest of the year, but that’s essentially what a lot of motorhome owners do when it comes to their generator.
A generator is comprised mainly of an engine, one that shares a lot of similarities with other engines including (in the case of a gasoline generator) a carburetor, air and oil filters, belts and other components. You may have grown accustomed to that power plant roaring to life whenever you push the start button, but all it takes is a few months of neglect and the generator can leave you in the dark — literally.
To get some expert advice on generator maintenance, we visited Smith Powerhouse Inc. in Bellflower, California, a factory-authorized service and warranty center for Cummins Onan, Honda, Kohler and Generac generators. Owner David Voloshin and shop foreman Matt Rudametkin are certified master generator technicians who have nearly 50 years of experience between them, and they’ve seen it all.
By far the most common motorhome generators in use today are the 4,000-watt Cummins Onan (known as the MicroLite, 4000, MicroQuiet 4000 and the RV QG 4000), 5,500- and 7,000-watt Cummins Onan (known as the Marquis Gold 5500 and 7000 or RV QG 5500 and RV QG 7000) and the Cummins Onan Quiet Diesel generators, so these will be the focus of this article. While the most frequent types of maintenance, such as oil/filter and spark plug changes shouldn’t prove too challenging for most DIYers (and can save some money), Smith Powerhouse recommends against more advanced maintenance procedures for two important reasons: One, you will likely do more harm than good if you don’t know what you are doing; and two, there are many ways to seriously hurt yourself. When it comes to major scheduled maintenance, it’s best to leave the heavy lifting to experts like Smith Powerhouse.
With all that said, let’s take a closer look at what’s inside those familiar green (or black) boxes.
| Another very popular motorhome gas generator is the 5,500- and 7,000-watt Cummins Onan generators, typically found in larger gas Class A motorhomes. It is a V-twin engine oriented on its side, with the valve covers facing up (the right cylinder is visible). Though it is a completely different design from the Cummins Onan 4,000-watt generators, many maintenance procedures are similar. Note, for example, that the oil fill/dipstick is in the same location as the 4000.|
| The air cleaner uses a paper element that is readily accessible from the front of the unit. Simply unsnap the clips and the cover comes right off. This filter element still looks good.|
| Draining the oil on the 5500 and 7000 is simple, since it uses a petcock instead of a drain plug. Warm the engine for about 10 minutes, then put a pan underneath and open the petcock; the oil is routed underneath the coach through a rubber hose.|
| Unlike its smaller brother, the twin-cylinder 5,500- and 7,000-watt generators do have an oil filter that looks like a small automotive filter. It is accessed through a hole in the bottom of the generator compartment. Both the replacement filter and handy wrench are available through Cummins Onan dealers.|
| The Marquis Gold has its spark plugs oriented on the sides of the cylinders (A), which can make them a challenge to reach. A swivel socket does the trick here. Removing the left (or No. 1) cylinder spark plug requires the removal of the air-filter assembly first.|
| Depending on the year and model, the 5,500- and 7,000-watt generators may actually have two fuel filters: this secondary one, near the carburetor, and a primary one at the fuel pump. Be sure to inspect your particular generator to see if it has two; Smith Powerhouse says a lot of home mechanics don’t know about the primary filter, so they don’t replace it and wonder why the generator still doesn’t run properly.|
| Diesel generators are typically located in the nose of the motorhome, so most of the items you’re likely to maintain in Quiet Diesel generators are located here, such as the oil fill/dipstick.|
|[2, 3] On Onan Quiet Diesel 6,000-, 7,500- and 8,000-watt generators, the radiator cap is located underneath a plate to the left of the coolant fill. Remove the fastener that secures the plate, then lift up on the plate and pull it toward you. You can then pull out the filler neck and remove the cap to check the coolant level in the radiator. Only remove this cap when the engine is cold; removing it when hot can result in severe burns.|
| The coolant fill is just to the left of the oil fill/dipstick. It is important to note that this is an overflow bottle, similar to the one next to the radiator on your automobile. Its level goes up and down depending on generator temperature, so just because it is full does not mean the radiator is full.|
|[5, 6] The air-filter cartridge is located underneath the unit at the front. It also uses two wing nuts — one for the housing, one for the filter, so don’t forget to replace both.|
| Cummins Onan Quiet Diesel generators are so reliable that people sometimes forget that they need maintenance. Allowing an air filter to get this filthy not only reduces performance, but can admit dirt into the engine that will cause damage over time. Just an FYI: Replacing a generator like this one is about $8,000, plus tax and labor.|
| The oil-drain plug on Quiet Diesel generators is located directly underneath the unit.|
| The oil filter (A) is accessed through an inspection plate underneath the unit. An oil-filter wrench may be required to remove it, and you’ll have to replace it by feel, but it’s not difficult.|