Join Date: May 2013
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Re: M25 what is this and where does the hose go?
You point me in the proper direction with the proper name. Google helped after that.
Earlier M25 engines had the crankcase breather tubes simply directed down below the engine. Later engines re-routed the breather tube to a spot near the air filter, so that the oily fumes are sucked into the engine when it is running. I was planning to do that myself (I have an '87 M25XP), until I talked to a Westerbeke/Universal rep at a boatshow. One of the "problems" with routing the breather hose to a spot near the air filter is that the oil fumes (from the crankcase) tend to get the air filter dirty at a faster rate. Instead, at the suggestion of the W/U rep, I took the intake manifold off, and drilled and tapped a hole for an elbow fitting. To that fitting I attached the other end of the breather tube. Now the oily air is sucked directly into the engine and bypasses the air filter. It has worked very well that way for the past 10 years or so. Others have simply attached their breather tubes to a spot near the air filter, and others have attached fittings to the air filter housing, all with good results.
Yes, that is the only good way to do it, you have to bypass the filter, and go directly through to the intake, and you want that to be a small fitting and small hose, so it does not suck too much oil out, which it should not do. I would replace the little filter inside the valve cover too, that way everything is working like it should.
It is good to learn from your mistakes, but much better to learn from the mistakes of others...