Weep Hole in Breather Tube?

A discussion came up at our EAA chapter meeting regarding weep holes in the breather tube.

My breather tube does not go out into the airstream; it stops over the exhaust pipe just short (in front of) the firewall. My thinking was that the risk of it freezing up were pretty slim, since it is up in the warm air. I have also not sensed that a weeping hole is common in the RV community.

What are others doing? Should I think about drilling a 1/8" hole? I have not had any issues so far and I have flown the aircraft in -10 degrees (actual), -30 degrees (wind chill) over 2 winters now.

IO-360
Minnesota (cold).

A whistle hole? Absolutely. The day the condensation freezes your breather tube, pukes out the oil, and causes an engine out landing (at best!) you will be reconsidering. For the very little amount of effort required, why wouldn?t you?

I am also a proponent of whistle-stop/breather holes in breather tubes -- particularly in cold climates. A plug of ice anywhere inside the tube can lead to a blown crankshaft seal and rapid loss of oil. Some oldtimers use a razor-blade to cut a thin slit halfway through the upper rubber portion of the breather tube that hopefully will allow pressurized air to escape in the event of a tube blockage. For a whistle-stop type of vent, drill a small hole midway on the downslope of the tube and bend the upper portion of the hole inward to minimize breather oil mist from exiting the tube during normal operation.

Good on the old timers

DHeal said:

I am also a proponent of whistle-stop/breather holes in breather tubes -- particularly in cold climates. A plug of ice anywhere inside the tube can lead to a blown crankshaft seal and rapid loss of oil. Some oldtimers use a razor-blade to cut a thin slit halfway through the upper rubber portion of the breather tube that hopefully will allow pressurized air to escape in the event of a tube blockage.

Click to expand...

I found this on a purchased certified AC, (mine was cut right through one side and about 2 1/2" long) I was concerned that it would leak slimy oil vapours, however after several years it stays very clean under the cowl. And I have landed in -15C temps with a ring of ice built up on the breather tube exit end (almost blocked). I am very happy to continue with the slit hose nearest the top end of the breather for safety.

Breather hole

I would drill the hole. I have always drilled one in a very cold area. We had engine failures in our Super Cubs without them. Yours is better on top of the exhaust, but there isn't a downside to the hole. 1/8 inch is enough.

In the hope of avoiding an mass hysteria.......

Let me point out the history and original purpose of the whistle hole.

There are many older certified aircraft where the crank case vent extended below the bottom of the firewall to where the tip was actually in the slip stream.

This was a problem because the temp. of the tip of the tube or hose was likely the same as ambient OAT. It is easy to understand that if the OAT is below 32 deg F, that moisture moving through the tube could freeze and block it.
A whistle hole was incorporated to prevent pressure buildup in the crank case causing the front crank shaft seal to be blown out.

Since the very beginning of Van's providing details/suggestions on engine installation, the breather tube has be specified to stay entirely inside the engine compartment with its outlet positioned directly above one of the exhaust pipes.
This is for a two purposes -

Oil that does exit the breather tube drops onto the hot pipe getting burned instead of coating the belly.

The end of the tube is always in an environment that stays above 32 deg F.

With literally thousands of RV's flying with this recommendation and zero instances (that I am aware of) of frozen closed breather tubes, it seems to be good evidence that if installed as recommended the system works well.

My personal RV and all of those that I am responsible for maintaining do not have a whistle hole because I have seen evidence of it causing a mess on the firewall.

Bottom line..... It is experimental aviation. People should do what they feel is right for them.... just pointing out that there is tons of evidence indicating that as designed, the hole is not needed.

If you have a breather installation that doesn't match Van's recommendations, it might be a good idea to have the whistle hole.

Here is a thread I started 12 years ago on this topic, my opinion remains the same
http://www.vansairforce.com/community/showthread.php?t=19931&highlight=manometer

I am still using this set up. It does require a whistle slot in the breather tube within the cowling. No oil drips have been noted in the cowling area from this whistle slot. I do get a drip on the hangar floor from the end of the tube. All the little annoying drops from various locations on the engine stopped.
There may be a reason all the certified planes have the breather extending aft of the cowling.

Regardless what pressure deltas are measured at different locations within the engine compartment, the important value is what the internal pressure in the crank case is.
I have been involved in numerous tests to measure the crank case pressure with engines that have the standard RV breather tube installed, using a custom made oil dip stick tube cap with a sense line port.
In all of the tests, the crank case pressure was way below Lycomings specified maximum, in all flight conditions.

Weep hole

I have an acs oil seperator.it came with 5/8? o.d. Hose connections. My lycoming io360 has a 3/4? o.d. fitting on the engine.can I use a reducer fitting on the engine and run 5/8? hose,or is that to much restriction in the oil vent. does the lycoming need 3/4? hose?
Thank you
Bob