Cummins Marine Diesel Repower Specialists Forums Cummins Marine Engines O Ring Diameter Conundrum 6BTA 5.9 330hp 1998 Era

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  • #76922

    Frank
    Participant
    Location: British Columbia
    Country: Canada

    I recently serviced the new to me aftercoolers as per the SeaBoard way. They looked in pretty good shape and I had no issues pulling the core and cleaning. I reassembled them using the 3/16 diameter orings though the ones that I took off were the small 1/8″. There didn’t seem to be a lot of squish resistance and the cap and housing met without much force applied. I chose the 3/16 because I read on this forum or perhaps boatdiesel.com that they don;t even order the smaller diameter rings anymore. I did find the 3/16 orings provided a lot of squish and needed torgued down quite hard. I took them in for testing at a radiator shop that does the aftercoolers for a large local boat yard. He too said he only uses the “fat” orings. Anyway they pressure tested ok and I installed them along with new hoses. In our first cruise in the new boat I noticed that my starboard aftercooler had leaded a small amount of water that was visible on the outside of the casing. Back at dock I ran up the engine and noticed a small drop of salt water coming out of one spot on the top cap about every 5 minutes. No other leaks on the bottom seal or other a/c. Should I go back to the small orings or try to tighten this one down some more? My concern is are there potential leaks go inside that I can’t see. I’d appreciate any advice you can give me.
    Thanks,
    Frank

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  • #76935

    Fireisland1
    Participant
    Vessel Name: Riverwind
    Engines: cummins QSB 380
    Location: long island n.y.
    Country: usa

    When you use the correct o ring, there is minimal interference. You may not even notice it when tightening down the bolts. If you put in too large of an o ring, the gap will be very noticeable and will require significant force to mate the cap to the case. If so this will deform and pinch the o ring.

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    #76930

    Anonymous
    Inactive

    Frank,

    On the aftercoolers o-rings, you always want to replace with the same as what came with the cooler originally. Although the “fat” o-rings can fit where the “thin” fit and vice versa, it is not recommended to switch. Using the “fat” when you actually need the “thin” can cause warping to occur in the cap (because of over tightening) and then you have sealing issues. If you use the “thin” when you need the “fat” means that there is not an optimal amount of sealing surface given by the o-ring and you will have sealing issues.

    If you are not sure which ones you really need, check out the article at the link below.

    B Series Aftercooler O-Ring Identification

    Thanks,
    Kevin

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