Vent hose for 912ULS coolant overflow bottle?

You have got me wondering the same thing! Maybe I can remove mine. 

If the overflow bottle needs to vent coolant, there is a more serious problem than the mess it will make if you don't vent it outside. Maybe the small amount of steam during normal operations will also make a mess over time. Perhaps this could be monitored and install a vent tube if deemed necessary. 

The fitting of the nipplle was for the Rotax overflow bottle specifically.  It is nice in that if an overflow occurs the fluid can be directed overboard and not dribble down the firewall and on to any hot objects.  Steam from fluid on to the exhaust would be a real problem for many installations.  For sure I read it as a suggestion that would be suitable on any overflow bottle or canister. 

Cheers

I agree with Murray.

The overflow bottle/expansion tank should, if correctly filled, never overflow in normal operation. In a serious engine overheat situaton, you have much greater concerns/problems than a coolant escape - the residue of which can easily be removed.

In the 15 or so years that I have been operating a Rotax 9's, the small hole in the cap of the expansion tank has, over a very long period, developed a small amount of a chalk like deposit.

The deposit is easily removed using water & a scrubbing brush.

I speculate, that trying to containe this, very small deposit, within a tube may be counter productive, in that the tube could block causing a pressure rise in the reservoir & associated tubing.

The installation of such a tube is an unnecessary complication - apply the KISS principle. 😈

I can tell you from experience that if you suffer from a situation where coolant is rapidly leaving the header tank via the hose to the expansion tank, then a tiny hole in the top of the latter will not be able to cope with the rapidly expanding steam and this will lead to a catastrophic failure of the expansion tank. Hot, high pressure coolant will be sprayed all over your engine which at a minimum will be a pain to clean up and at worse will enter electrical connections and damage other more sensitive parts under the cowling.

I agree that it normal operation this is not a concern but it can happen and it has happened to me. You need a reasonably generous vent hole and discharge pipe to allow this to safely exit the expansion tank and your enging bay. All of the fittings need to be robust and able to withstand temperature and pressure.

Thanks Gentlemen, for your replies and comments.  I tend to look closely at the Rotax recommendations, ask questions and then make a decision...