Discussion in 'Bigger Boats' started by twodzusfittings, May 11, 2019. Add this thread to a FAQ

  1. twodzusfittings


    Joined Aug 11, 2011
    424 posts, 16 likes
    O'day 30
    313 US Sassafrass River, MD
    I'm in need of recirculating the crank case breather hose. The original air filter housing does not allow for direct line in, but appears the design and position of the breather hose, is that of in my humble opinion; as the end of the hose and the mouth of the air intake housing are in close proximity, suction is created and the crank case gasses and dust is sucked in to be recirculated.
    However, this system is open and gasses and dust are escaping into the engine compartment, leaving smell and a fine coating of oily dust. I would like to eliminate this for a cleaner boat.

    My thoughts are to locate a filter kit, similar to an K&N that has a pcv valve built in. Or does the wisdom of the owners forum have alternative methods to achieve my intended results?
    Open minded to all ideas except getting rid of my boat. (My wife's idea!)
    IMG_2544.JPG Air intake cover is the lower left oval thing. Shows how the breather hose runs along side.

  2. Sefuller


    Joined May 6, 2010
    368 posts, 62 likes
    Oday 34, 39
    US Milwaukee
    Here is an implementation of the method @Maine Sail illustrated a couple of years ago. This boat is still a work in progress but it should give you an idea as to how to solve the breather problem. The separator is available from Jegs, and the filter is a K&N. Originally the breather was routed just like yours.

    Attached Files:

  3. LeslieTroyer


    Joined May 20, 2016
    2,619 posts, 1,229 likes
    Catalina 36 MK1
    US Everett, WA
    I have a setup similar to @Sefuller oil separator to k&n filter with the base drilled to accept a hose fitting.

    Attached Files:

  4. Richard19068


    Joined Jun 11, 2004
    783 posts, 75 likes
    Oday 31
    US Redondo Beach
    This K&N filter fits directly on the air intake of my Universal M-18. It come with a hole in the top into which you can screw a hose barb fitting. I have the same JEGS air oil separator that Sefuller shows above.

    This combination has worked great at keeping the blow-by out of the engine compartment.

    As noted in another thread though the K&N filter is louder than the stock "silencer" so there is a trade off.

  5. Stu Jackson

    Stu Jackson

    Joined Feb 26, 2004
    20,531 posts, 950 likes
    Catalina 34
    224 CA Maple Bay, BC, Canada

  6. eherlihy


    Joined Aug 17, 2010
    170 posts, 25 likes
    Oday 35
    US Barrington
    20190425_140728.jpg I recently addressed this problem on my M25. I added an oil "Catch Can" that I bought for ~$20 on Amazon. The catch can stores any of the condensate that used to simply vent into the engine compartment behind the alternator. I believe that the soot and oil, which comprise most of the condensate, had been drawn through the back of the alternator by the alternator cooling fan. The soot likely had been conducting electrical current where it should not have gone, and was contribuiting to the fact that I was completely eating 2 Aluminum anodes every three months. Not shown in the picture above is that another blue hose goes from the catch can to the air filter.

    The problem with running the breather hose directly to the air intake is that IF there is a malfunction of a piston ring, or if you overfill your oil (I found that I had been doing this for about a year), then you risk a diesel engine runaway situation.

    [EDIT] after following Stu's links above, I see that Maine Sail agrees with my concern, and reccommends a catch can; 'In order to avoid a run-away diesel or excess carbon, it's a good idea to put a "trap" in the PCV line before it hits the manifold or air filter. Even a cheap in-line filter for an air compressor will work to capture any oil before it gets to the manifold. These are often called "oil/air separators" or "oil catch cans".'

    Last edited: May 14, 2019

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