Let the engine breathe - breather hose to air intake redesign

August 1, 2011
breather hose jammed into air intake
Universal M25 diesel with breather hose into air intake

A couple of years ago a buddy suggested I put a nipple on the air intake on my Universal M25 and attach the breather hose to the nipple. What he was looking at was the breather hose from my valve cover stuffed directly into the air intake, apparently a completely acceptable method to eliminate the blow-by smell from these engines – the gases go right back into the intake manifold and so does any oil. My diesel go-to guy had fixed it up that way back in 2004 and I never gave it another thought. The engine seemed to run just fine and it certainly didn’t have any blow-by smell.

Time for a change

air / oil separator kit from JEGS
JEGS air / oil separator kit

I’d bookmarked Compass Marine’s Air Filter & PCV Valve Upgrade some time ago and now revisited that website and various forum threads on the subject, but a complete redesign of the air filter on Reality Check wasn’t going to happen, at least not by me!

After cleaning the air intake part and taking a look at the breather hose that had a nice coat of oil on the inside, keeping the blow-by oil out of the manifold sounded like good diesel practice… hmm, the JEGS air/oil separator looks perfect for this application and I don’t have to fabricate anything.




air oil separator with filter
Air / oil separator with filter

Before I ordered this part I made sure there was a place I could put it – the polycarbonate bowl can’t touch any hot surface. Not only did I have plenty of room, the location in the engine compartment is easy to get to when the filter needs cleaning.

The JEGS air/oil separator came with connectors that screwed into the unit at one end and had a hose barb at the other. The hoses I was connecting were 1/2″, too big for the barbs. I replaced the JEGS barbs with 1/4″ nipples from Home Depot. Perfect!

universal m25 breather hose to air oil separator
Breather hose tied to air intake with a nylon cable tie



How about a nipple on the air intake? Couldn’t find a part to make that work – if I were to drill a hole in the intake cover and stick a nipple in there, there aren’t any nuts that fit nipples in order to hold it in place (nipples are plumbing fixtures, they don’t have nuts). An easier solution was to cut the hose in two places and slip a cable tie over the cut hose to hold it next to the air intake. I like easy


air intake without cover
Clean air intake part (#301138) without cover



Of course BEFORE I tied the hose, I cleaned up that air intake and put a new foam filter over it.

air intake with filter
Air intake with foam filter part #301049


JEGS air/oil separator kit #52205 – $57 ($47+ $10 handling)

3 feet of 1/2″ heavy duty water hose – 2 1/2 feet of hose from the valve cover elbow to the JEGS air / oil separator, and about 6″ from the output of the air /oil separator to the side of the air intake – West Marine #135 – $4

2 nipples – 1/4″ brass hex nipple fitting #A-729- Home Depot – $5

2 stainless steel clamps

Foam filter (Universal #301049) – A-Z Marine $10.46

Photos of this project

Breather hose to air intake photos

Related topic: Breather hose to air intake redesign revisited


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