Most manufacturers recommend purging the system of fuel and disconnecting the fuel line, as well as removing the spark plugs and adding a touch of motor oil to each cylinder. It is generally felt that these major steps are not required, providing the other actions in this article are undertaken. It is especially important to periodically run (exercise) the generator as outlined here. If you are unable to exercise the generator on a regular basis (at least once per month), especially if it will be in storage for an extended period, following all the manufacturers advice is recommended.
It is a good idea to perform a full oil and filter change prior to putting the generator in storage. This ensures that the oil is clean, preventing particulates suspended in dirty oil from settling on engine components. It is also a good opportunity to inspect the spark plugs, air filter, as well as external wires and hoses for wear or damage. A quick external wipe-down is not a bad idea.
If you have a gas or diesel generator, be sure to add the appropriate stabilizer to the fuel tank and run the generator for several minutes to allow the stabilizer to enter the genset. Make sure the fuel tank is at least ¾ full at all times during storage. This prevents condensation from forming in the tank. These steps are not required for LP (propane) generators.
As indicated above, the key to keeping the generator healthy during periods of inactivity is to be sure to exercise it at least once per month (two week intervals is better). This should be done at high current load (at least 20 Amps). Note that it is never a good idea to start or stop a generator with a load applied. Some transfer switches and energy management systems prevent loads from being applied to the generator during start-up, but your system may not be so equipped. Ensure all A/C sources are turned off (such as air-conditioning, washer/dryer, fridge, water heater, etc.) during generator start-up and shut down. Once the genset has a chance to stabilize after start-up (15-20 seconds is my recommendation), apply enough load to create a 20-30 Amp draw. If you have an air-conditioner with a heat-pump option, this is a good load source. I will assume that the generator storage is occurring during cold winter months, but if not, the air-conditioner itself can also be used as a load. If you don’t have a heat-pump, I recommend using portable space heaters, hair dryers, and the like. Even if you are using the heat-pump, it is still a good idea to add extra load. The goal is to fully exercise the generator in order to keep the engine components and seals, as well as the generator itself, from deteriorating due to lack of use. Once you have sufficiently loaded the generator, allow it to run for 20-30 minutes.
These simple steps will help ensure your generator stays healthy during storage and is ready to be called into action when your next RV adventure comes calling.