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  1. #1
    Big Traveler
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    What is the correct oil amount in an Onan 5500?

    I've seen plenty of posts that say "to the top" fill it until it won't take a drop more. And if work to get all 2Q in, it's FULL. Honestly, there's no reason for a dipstick at all, if that's the right level, it's full right to the brim.

    That seems to be the most commonly recommended answer, fill it until you can't get any more in. But then, there are also people like this who have trouble with that, up to the point of saying the dipstick is defective:

    https://www.youtube.com/watch?v=vzXDlln8aUw

    I'm not even going to say my experience is normal, I know I have another generator problem that's not oil, but it does seem that if I fill it to the brim I get more shutdowns.

    I'm just wondering, what's the "real" answer here. I think it's "as much as you can get in", but I just want to make sure.

  2. #2
    King Pin
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    What does the owner's manual say? Not being a smartass, just wondering what it says. I have one, and have changed the oil and I filled it according to what the manual said, but I don't remember
    what it actually said.
    Howard and Peggy
    2019 Momentum 351M, and 2018 RAM Cummins dually 6-speed.
    His: 1999 Honda Interceptor
    Hers: 2013 Spyder ST-S

  3. #3
    Long Hauler geotex1's Avatar
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    It's 2 qts with filter. Gotta dump the oil hot, be level, and take the dipstick out while draining. It drains SLOWLY. You'll get about 1.5 to 1.75 qts in, and then have to run it to top off. The level is really high on the dipstick too when full.
    Rob & Nikki + Cloverfield
    2020 Grand Design Solitude S-Class 3350RL
    2015 RAM 3500 Longhorn Laramie Crew Cab, Long Bed, 4x4 Dually Cummins/AISIN

    Mountains of Pennsylvania

  4. #4
    Big Traveler
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    Quote Originally Posted by Hoopy Frood View Post
    What does the owner's manual say? Not being a smartass, just wondering what it says. I have one, and have changed the oil and I filled it according to what the manual said, but I don't remember
    what it actually said.
    It says 2Q with filter. And I was able to get that much in. Thing is, I've heard (as you may have seen in the link) that too high causes shutdowns. I've also heard too low causes shutdowns. I've also heard that the dipstick they have with the 5500 is defective (the markings) and the "full" level should be lower.

    I wouldn't give any credence to any of that over the manual other than I've never, in my close to 40 years of working with and maintaining small engines seen an oil setup like the Onan. If you're dripping oil into a fill hole and it's overflowing, you're doing something wrong. Oil should never be spewing out the check port when you open it. The Onan just goes against everything I've seen in dozens of other similar small engines. And a lot of engines like the Onan have explicate "DO NOT OVERFILL" warnings on them.

    I may run it tomorrow to get it hot, let it drain for a day, and then measure exactly 2Q of oil (change the filter too, of course) into the engine. That way I know it's "right", no matter where it lands on the dipstick.

  5. #5
    Long Hauler geotex1's Avatar
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    Part of the problem is lousy mounting. The coach may be level, but the generator not. It WILL shut down if oil pressure builds too high. My experience has been this happens when someone didn't get a good drain and oil remained then they got 2 qts in by way it was sitting. Another thing is using some cross-reference full filters versus than Onan filter as some don't have as much capacity though looking physically identical. When I change mine in my enclosed hauler, I have a graduated drain pan. If I don't get 2 out, I figure out why before I add. I also use full synthetic and have been since I bought that trailer 7 years ago and did the initial run in.
    Rob & Nikki + Cloverfield
    2020 Grand Design Solitude S-Class 3350RL
    2015 RAM 3500 Longhorn Laramie Crew Cab, Long Bed, 4x4 Dually Cummins/AISIN

    Mountains of Pennsylvania

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