Change the Oil in Your Onan Diesel RV Generator

TheRVgeeks Annual Maintenance, Generator, Maintenance 10 Comments

One of the greatest freedoms we get from RVing is the ability go anywhere, any time, completely self-contained. Our Onan 7.5 kW QuietDiesel RV generator is a key part of that freedom. Proper care and maintenance of the “genny” will lead to a long life of trouble-free operation.

Each spring, we service our genset as part of routine spring cleaning. The oil and oil filter get changed every year, along with cleaning the spark arrestor. Some years also call for air & fuel filter replacement and coolant system service too. Generator service intervals are based on time or hours they’ve run, but we generally don’t use our generator enough to need service more than once a year.

We take care of all of these items ourselves, and in nine years of RVing, we’ve never had anyone else work on our Onan. We have never had a day of trouble with it, and the routine service is so easy that we’ve never needed any outside help. We’ll cover the three most basic service items here.

We just changed the fuel filter last year, so we won’t be demonstrating that today. And the cooling system service is involved enough to require its own video, so we’ll be covering that within the next few weeks. In this video, we’ll show how to change the oil & filter, replace the air filter and clean the spark arrestor.

From everything we’ve heard and read, the single biggest cause of generator trouble is lack of regular use. There are times when we’re hooked up for fairly extended periods and don’t need the genset, but we make sure to exercise it regularly anyway. The generator should be run at least once a month for about 2 hours under about half load. This means firing it up even if it’s not needed for power, and turning on both air conditioners (or heat pumps) and heating a tank of hot water, or plugging in our portable space heater.

Whenever staring the generator, be sure to let it idle for a short time to warm up before putting a load on it (turning anything on that draws power). Also, before shutting the genny down, be sure to turn off all loads first, then let it idle for about two minutes to cool down before shutting it off.

Our generator will likely see more use this coming year than ever before. After being hooked up all winter, we’re about to spend our first year out on the road with a new residential refrigerator that recently replaced our dead Norcold.

Our Onan (an extremely popular brand) is a diesel model, and runs off the same fuel tank as our engine. We have no experience with gas generators or other brands, so many things about them may be different than ours. Be sure to follow your manufacturer’s instructions for operating and maintaining your generator.



We're handy RVers, not professional technicians. We're happy with the techniques and products we use, but be sure to confirm that all methods and materials you use are compatible with your equipment and abilities. Regardless of what we recommend, consult a professional if you're unsure about working on your RV. Any task you perform or product you purchase based on any information we provide is strictly at your own risk.

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Comments 10

  1. Great step by step! I would recommend keeping your face well clear when removing the spark arrestor… don’t ask me how I know that.. :)

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  2. Hi,

    I’m so glad I found your site explaining generators. I’m a 71 year old newbie to everything RV and am desperate to learn how my (new to me) 2001 Pleasure Way (56,000 miles) works. A DIY-er who can fix anything on my house, except electrical. So I’ve become familiar with most of the workings EXCEPT the Onan MicroLite 2800 series generator which runs on gas.
    My problem is that the generator will start, but will not stay running. Of course I’m to leave on a 5,000 mile trip next week and don’t want to do so without a working generator. Can you suggest a cause and/or solution?

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      Hi Kay! Congratulations on becoming an RVer at 71! Good for you! And especially great that you’re a DIYer to boot. :)

      We’re not mechanics, but we know that the two primary things that make a gas engine start and run are spark and fuel. Since the engine is actually starting, it means that you have spark. That leaves fuel as the most likely problem. Based on what you’re describing, we think that (assuming you’re sure there is gas in it, and that the gas isn’t several years old) a very likely culprit is either a clogged fuel filter, or a fuel pump problem.

      Our friend Brian, of http://RVwithTito.com has an Onan Microquiet 4000 generator (also gas powered) in his RV, which he maintains himself. We’re assuming that his is similar enough to yours that he would know more about it than we do. So we’re sending Brian an e-mail right now, asking him to view this thread and see if he has any suggestions for you. We’re not sure where he and his wife Melissa are this holiday weekend, so hang in there while we reach out to him. He’s a great guy and we’re sure he’ll be happy to try to help if he can.

      In the meantime, here’s Brian’s video about testing and replacing the fuel pump, which may help: https://www.youtube.com/watch?v=U72Zmk0BF-o

    2. Hi Kay.
      Your 2800 is a little different from my Onan 4000 but I found a photo to help. Based on your description, I would agree that your problem is fuel related. Your carburetor is probably being starved of fuel. To troubleshoot this problem, I recommend first verifying that you have sufficient fuel in your tank. Most RV generators don’t run if the gas tank is below a quarter tank.

      Before troubleshooting, I recommend draining any remaining gas from your carburetor. You can do this by slowly unscrewing the screw just below the altitude adjustment on your carburetor. Place a small container below the carburetor to catch any fuel that comes out. Then tighten the screw.

      Now start the generator to see if it starts. If it starts, runs for a bit, then shuts down, then immediately proceed with the fuel pump test outlined in my video (mentioned above) and replace the fuel pump if necessary. If it doesn’t start at all, then it’s probably your carburetor which may need to be serviced or replaced.

      To locate your fuel pump, follow the black fuel line down from your carb. It leads to your fuel filter, then to your fuel pump (probably below under other stuff). Your fuel pump is connected to your gas tank.

      Those are the steps I would take to troubleshoot your generator. I hope it is helpful. Take care and good luck!

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  3. I only have about 30 hours of use on my generator.I have a 2014 coach.Do i have to change oil and filter now or can i wait until i add more hours of use?

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      Hi Bob! Even if you haven’t hit the hours interval for oil & filter change, the generator is just like any other engine, with time also being a factor. Regardless of hours, the oil & filter need to be changed at least once every 12 months. As far as running the generator, the worst thing you can do it let is sit unused for too long. If you haven’t used it very much in 30 days, fire it up, warm it up, and put it under a pretty heavy load for at least an hour. By “heavy load” I mean a couple of large-draw items like the water heater, plus an air conditioner or heat pump (or two). This kind of exercise is what keeps the genset from getting “lot rot” from lack of use. We always remember what a technician told us early on… the most troublesome older generators he works on are the ones with the fewest hours on them. We’ve exercised ours at least once a month for 10 years and have never had a moment of trouble with it. (hope I didn’t just linx myself!) LOL

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