my crankcase oil breather line and fuel pump bypass solution

The subject of how Vans supplies a non-oil compatible heater hose to serve as a breather line has been discussed to death, but I thought I'd throw out my solution on a new thread in case it might help somebody out in the future.

My engine came from Lycoming with a brass 3/4" nipple installed in the breather port. Vans would have you cut a rubber elbow off a Napa automotive heater hose and connect it between this fitting and the end of their aluminum down spout which is necked up at the upper end specifically to allow it to mate to a 3/4" hose, then immediately chokes down to 5/8" for the rest of it's run.

The issue people have with this is that the heater hose isn't rated for oil products and will degrade over time, much more than a suitable material.

My solution was to just replace the straight 3/4" brass nipple with an AN844-10 that I got from Airparts for about $20. Yes, it can be done on an engine thats already hung (barely).

I then cut the vans downspout right below the upper curve and just used the bottom part. I attached it at the vans print location and at the engine mount with adel clamps, and connect the AN844 and the downspout with about 18" of Mil-6000 hose.

I don't have the exhaust yet, so this may need to move up a bit for clearance, which is why there aren't any hose clamps on the assembly, nor have I drilled a whistle hole yet.

The clear vinyl line is the drain for the fuel pump bypass. For a fitting, I just used a 1/4" hose barb from the plumbing section of Ace hardware.

I elected to try a vinyl hose here because it's clear and I'd like for it to be obvious if fuel is starting to bypass.

I looked up the specs on vinyl and it's good to 160* which seems like it should be plenty. However, this routing has it passing within about 1" of the oil cooler so I'll keep an eye on it and if it seems like it's getting too hot there I might replace it with something more robust in the future.

I hope that if somebody is looking for an alternative to the factory solution this might be of some help.

I had my breather tube just like that over the exhaust pipe inside the cowl. I developed an oil leak from oil being pushed into my right magneto from excessive crank case pressure. Also my oil return lines from the cylinders were leaking.

I was advised by my mag overhaul company to change my breather tube outside of the cowl.
I did and have no more oil leaks and no blow by.

I know that some guys have reported that being an issue, but this is per print and I've seen a lot of airplanes with a similar setup over the years that have had no problems with oil leaks. I'm going to give it a go this way. if it's a problem, I'll change it later.

Thanks for the input

Zero4Zulu said:

I had my breather tube just like that over the exhaust pipe inside the cowl. I developed an oil leak from oil being pushed into my right magneto from excessive crank case pressure. Also my oil return lines from the cylinders were leaking.

I was advised by my mag overhaul company to change my breather tube outside of the cowl.
I did and have no more oil leaks and no blow by.

Click to expand...

Hmmm. Think about it.

A breather tube ending inside the cowl doesn't change the difference between internal case pressure and exterior case pressure. An exit restriction increases internal pressure, but leakage due to pressure is a function of the deltaP.

Engine Breather line Pressures

Fun stuff with breather lines
As I have an inverted system in my RV6 I have the breather on the gear leg to reduce mess. As I quickly found out if you back cut the tube with relationship to air flow it causes a negative pressure in the crank case an you loose a quart of oil every flight ! forward cut it and you can pressurize it and cause leaks !
so after 20 flights I found 54 Degrees foward cut worked for me . I used a Airspeed indicator to measure inches of water pressure in the crankase with an oil dip stick adapter to put a hose on to the extra ASI in the cockpit

Moral of the story don't point the breather hose into the air flow you can pressurize the system possibly push out your front seal, on non inverted systems leaving it in the cowl can work, remember to have a cut somewhere in case you get an Ice clog on the exit end.

hope this is of help

Peter

petercavallo said:

Moral of the story don't point the breather hose into the air flow you can pressurize the system possibly push out your front seal,

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Makes sense. Down low at 200 KTAS, pitot pressure would be >25" H2O. Even if lower cowl pressure was 10", as it might be with a restricted cowl exit, delta would still be 15". IIRC, the Lycoming limit for case pressure delta is 4".

DanH said:

Makes sense. Down low at 200 KTAS, pitot pressure would be >25" H2O. Even if lower cowl pressure was 10", as it might be with a restricted cowl exit, delta would still be 15". IIRC, the Lycoming limit for case pressure delta is 4".

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Doesn't pressurizing the crankcase also rob power? I'm pretty sure the "go fast" guys are putting a slight negative pressure on their breather lines. Anyone?...

Vent

I was disappointed by the Vans solution as well

The vent on the engine was fine.
I bought this power steering hose.
Edelmann 80576 Molded Power Steering Hose
The flared end of the tube was cut off. Tube filled with sand and straightened out. Cleaned. Mounted in the Vans location. Hose trimmed so it fits from the breather to the tube with a few inches of rise. Bottom ended right above the exhaust. Hole drilled 6" above the bottom of the tube as a freeze relief.
The advantage is the hose comes off with two clamps to gain access to the back of the engine.

For those with concerns about the quality of the hose, I have used parker 15866 which is resistance to oil and other contaminate as well as required temp with great success. The first hose has been in service for 5 years with zero sign of softness/issues.

rmarshall234 said:

Doesn't pressurizing the crankcase also rob power? I'm pretty sure the "go fast" guys are putting a slight negative pressure on their breather lines. Anyone?...

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Auto racers are real serious about case evac systems, pulling 15" negative, maybe more. There are dyno plots out there saying it works. However, I would not want numbers that low. There is the possibility of pulling dirt in past lip seals, and it subtracts from engine driven fuel pump pressure. Low single digits for me.

Bavafa said:

For those with concerns about the quality of the hose, I have used parker 15866 which is resistance to oil and other contaminate as well as required temp with great success.

Click to expand...

Same here, using Parker 801.
.