In my last post, I wrote about getting a generator up and running. The main reason this generator quit working was lack of use. Regularly exercising a generator should be part of the preventive maintenance schedule. Gasoline-powered generators can suffer fuel system maladies such as varnished carburetors from fuel evaporation. Gasoline also has a shelf life. Although gasoline is formulated with stabilizers, it will deteriorate over time. Gasoline is made up of many compounds. Some of them are light and volatile while others are heavier and less volatile. The light, volatile components evaporate first and over time, the chemistry of the gasoline changes.
Running the generator on a regular schedule keeps fresh fuel running through the fuel system. The fuel in the tank should be replenished every six months or so – maybe longer if additional stabilizing additives are used.
The generator needs to be run under load – it should power electrical consumers that equal about half of the output capacity. This allows the engine to run at full operating temperature and also warms up the electrical windings and removes corrosion from electrical contacts. The oil circulating in the engine will prevent internal corrosion. It needs to be run long enough to get the oil up to operating temperature. I would say half an hour is the minimum. The manual for our Onan Quiet Diesel 7.5kW generator suggests two hours of run time per month.
Yesterday I performed another part of the scheduled preventive maintenance on our generator. I changed the engine oil and oil filter. The maintenance schedule for our generator calls for an oil and filter change every 150 hours. We have a meter on the start switch on a panel in our coach that records the generator run time. Whenever the generator is running, it records the time in increments of 1/10th of an hour.
Generator start switch and hour meter
The last time I changed the oil and filter in our generator was last September. In 11 months, we put 150 hours on our generator. If we hadn’t hit 150 hours, I would consider changing the oil at 12 months. The generator engine isn’t especially hard on oil. Engines that don’t spend much time idling or running hot at high load are easy on the oil. Also engines that come up to full operating temperature each time they’re used are easier on the oil than engines that are run for short duration.
The crankcase of the engine condenses moisture from the air as it cools down. Over time, this moisture contaminates the oil. In extreme cases, it can form an emulsion and hinder the lubricating ability of the oil. When an engine is regularly brought up to full operating temperature and the oil temperature reaches or exceeds 180 degrees Fahrenheit, the moisture in the crankcase or in the oil is converted to steam and driven out of the engine.
If an engine is regularly run for short durations and the oil temperature stays too low – 150 degrees or less – it will have excessive moisture in the crankcase and should have the oil changed more often.
Our generator is usually run for at least an hour at a time and always gets up to full operating temperature. Every time I’ve drained the oil from it, I haven’t see any sign of excessive moisture. Lately we’ve been running the generator as we drive down the road to operate our roof-mounted air conditioner. This makes it a much more comfortable ride in hot, humid areas. It also ensures plenty of exercise for our generator.
Some modern cars have oil service indicators that customize the oil change schedule. These systems don’t actually sample the oil for condition. They monitor the driving conditions such as how much time is spent idling and what the temperature of the engine and environment are. Plugging these factors into a table, it comes up with a recommended oil change interval.
Today we plan to go to the farmers’ market at Bolton Landing (map). Donna’s sister Pam and her husband Gene will join Tom, Linda and us to shop there and go out to lunch. This afternoon, I’ll start preparing the coach for travel – I want to pull out early on Sunday.