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  1. #1

    Default Onan Engine Question

    Quick question regarding Miller engine driven welders with the Onan engines in them (or any other small single or twin cylinder engine).

    How often (how many hours) do you pull the heads on your Onans and decarb the engine?

    Reason I ask is I've got an Onan that has about 400 hours on it. It is a twin cylinder aluminum engine, Performer P220 and is twin cylinder. The engine runs like a champ, but I've been advised to pull the heads and clean the carbon as a preventative measure. I've also read horror stories about folks doing this and twisting off tin and head bolts trying to get the heads off.

    So my gut says, if it ain't broke, don't fix it. Somehow I need to address potential carbon build-up.

    How often do you pull the heads on your Onans to clean the carbon or do you just run them forever?

    On another note, is there anything you can do to minimize the carbon build-up in the first place? I've read some use MMO or Seafoam or spray a mist of water into the carb to burn out the carbon.

    Any advice, tips, tricks would be much appreciated.

    Thanks,
    Bill
    Bill
    Miller Dialarc HF

  2. #2
    Join Date
    Oct 2005
    Location
    North Central Indiana
    Posts
    782

    Default

    I'm no expert on Onans,just a thought. Could you pull the plugs and see what they look like? If the engine runs fine and the exhaust doesn't smell rich or smoke all the time.... and the plugs look clean I wouldn't touch a thing.

  3. #3
    Join Date
    Oct 2004
    Location
    Edmonton, Alberta
    Posts
    7,760

    Default

    Ahhhh, never......

  4. #4
    Join Date
    Sep 2012
    Location
    seaford de
    Posts
    406

    Default

    Run Lucas fuel system treatment through it. Its pretty good stuff. I put a little bit in all the gas I buy because of ethanol probs. And once a month I do the suggested full treatment

  5. #5
    Join Date
    Aug 2004
    Location
    Milan Michigan
    Posts
    1,705

    Default

    I've got a 1995 Onan on my trailblazer with about 2500 hrs on it and its been the best running engine that I have had yet.

    Change the oil, filter and spark plugs, Ive never used the fuel treatments myself but I doubt that it would hurt.

    Would you pull the heads off your new truck at 18,000 miles because thats the equivelant of 400 hrs.

  6. #6
    Join Date
    Dec 2012
    Posts
    7

    Default cruizer

    Been trying to message Cruizer to see about sending you my 375 X-treme for diagnosis ?

  7. #7
    Join Date
    Mar 2006
    Location
    La Porte, Tx.
    Posts
    56

    Default

    You won't get a better de-carbon cleaner than the BG product line,,, like a BG44k you add to your fuel ever so often,, good stuff for not having to pull the heads. If your burning that crap ethonal 10%, no getting around the carboning, wait till the gub-mit makes us burn the e15.....
    pull-do

  8. #8
    Join Date
    Feb 2009
    Location
    Lodi, CA
    Posts
    1,273

    Default

    I've had many hours with the old cast-iron Onans, various mobile equipment. They had a tendancy to carbon-up the heads. Since using the aluminum block/head Onans for the last 20-30 years or so, in engine-drive welders and generators, I haven't seen this happening ever.
    Obviously, I'm just a hack-artist, you shouldn't be listening to anything I say .....

  9. #9
    Join Date
    May 2011
    Location
    Bossier Parish La.
    Posts
    549

    Default

    Who was it exactly that advised pulling the heads in the first place? Never heard of doing this to an engine that as you say "is running perfectly fine". If it were displaying some symptoms of a malfunction, it might be more understandable, but not on one that is running good. I think you are looking for a problem that does not exist, but may find, if you start tearing into it just because someone advised it. Maybe this guy don't like you and you don't know it yet.

  10. #10
    Join Date
    Sep 2012
    Location
    Coastal Maine, Coastal NC
    Posts
    21

    Default Onan Engine De-Carb

    I had a John Deere tractor with an Onan 18 HP engine in it that I got in 1986. We used the tractor was used in commercial lawn service and for my own driveway snow plowing. At about 1500 hrs, I pulled the engine to get at an oil leak and pulled the heads since they were right there and easy to get at. It was a waste of time. There was no significant carbon in the chambers and the valves were still excellent. I put the heads back on and put it back in service.

    At 2200 hours I sold the tractor and it was still running perfectly and still was not using any oil between 100 hour changes.

    Unless something is not working properly, just leave it alone and run it. Change the oil and filter regularly. It may run forever.

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