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Aug 11, 2011
O'day 30 Feeling Nauti GEORGETOWN, 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.
May 6, 2010
1984 Oday 39 79 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.


Jun 11, 2004
Oday 31 Redondo Beach
This K&N filter fits directly on the air intake of my Universal M-18. https://www.knfilters.com/search/product.aspx?prod=RE-0240 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. https://www.jegs.com/p/JEGS/JEGS-Air-Oil-Separator/763433/10002/-1

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.
Aug 17, 2010
Oday 35 Barrington
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".'
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