ID of line from 914 expansion tank->coolant overflow bottle? (YADQ)

 "..........everything from a few wraps of 041 to zip ties. Thing to remember is to vent the bottle overboard and away from the airplane."

Its part of the human condition to overthink/complicate things. 

Here we are having a ridiculously earnest debate on such a simple system -  crazy!

The function of the tube is to convey hot expanding coolant to the reservoir/overflow bottle AND then back again, when the cooling system cools - simple!

To achieve this one end of the tube must be securely (air/liquid tight), the other end immersed in the overflow fluid, such that no air can enter.

You can achieve this in a few ways (already canvased) - no secure system, using appropriate materials, will be better or worse.

There may be added expense (not much) and complexity that could increase the chances of failure.

If you aspire to the "gold standard" - go for it. It will have nil effect on aircraft efficiency or safety.😈

Think of it this way, Sean. You've got someone like me who can change the oil in his car but is now working on something worth more than his 25 year old car, and if done incorrectly could kill himself and loved ones, not to mention unknown people on the ground. Though I've been to 2 Rotax classes in separate locations, there's still a LOT I don't know, and not using this resource to ask questions would be foolish. 

:cheers:

All good Steve - however I come back to the simplicity of this system.

Just think it through and make your own decision, on how complicated you really want  to make it.

While a faulty overflow tube/fittings has the potential to cause coolant to be expelled overboard -

The pilot should pick this up in the pre-flight inspection, (most coolant will leave tell-tail stains & the reservoir level may have changed) so damage to the engine is unlikely

OR

If occurs in flight , smell, possible white smoke on climb out, may suggest you return to the field, however once again the chances of engine damage is low, as the bulk of the coolant will remain in the system.

As the maintainer you have discretion on what & how you do it. For most service/repair/installation I go with Rotax recommendations. I also use common sense/experince (double wrap safety wire, twist of with care not to damage hose) to secure hose to spigot.

The overflow bottle & tube can, as I have articulate, be simplicity itself  (no extra fittings) OR you can go to the other extreme, have connectors & elbows, bottom of reservoir connection point OR something in between - non of its wrong. It all does the same job.😈