mysterious hole in plenum

[Geezeravi8tor]

A prior owner drilled a neat 1" hole in the "filler neck" of the air plenum on my Rotax 912 -- see attached picture. Traces of RTV around the edges suggest someone subsequently tried to seal the hole. I'd like to complete the job of sealing the hole as it seems to me to reduce the flow of cooling air to the engine, which can't be a good thing. But, maybe there's a reason for the hole? Any ideas

[Jamesey]

If it’s an “oldie” it was probably the tap off for a tube to cool the regulator originally mounted on the firewall shelf

[seagull]

I have removed the plenum completely, didn’t notice any difference in temperature.

[cactusman]

Originally Posted by Geezeravi8tor

A prior owner drilled a neat 1" hole in the "filler neck" of the air plenum on my Rotax 912 -- see attached picture. Traces of RTV around the edges suggest someone subsequently tried to seal the hole. I'd like to complete the job of sealing the hole as it seems to me to reduce the flow of cooling air to the engine, which can't be a good thing. But, maybe there's a reason for the hole? Any ideas

Yep I still have tube that attaches there and blows on my original John Deere regulator.

Just out of curiosity where is your regulator located now?

[hgerhardt]

Originally Posted by seagull

I have removed the plenum completely, didn’t notice any difference in temperature.

All of the Slings with 915iS and 912 have no baffling of any kind. Just two small cowl inlets which blow willy-nilly into the cowl cavity and a big exit at the bottom rear. And the air-cooled cylinders seem perfectly happy with that (the heads are water-cooled).

[Geezeravi8tor]

My regulator is located atop the footwell on the pilot's side. Thanks to all who responded to my original inquiry. I'll be sealing the formerly mysterious hole now.

[DHeal]

FWIW, I rerouted/repurposed the aft end of the former regulator cooling hose to blow air onto the ignition module stack. I figured that a bit more air on the two modules would help keep them a bit cooler -- after 1,000+ hours, so far so good.

ps -- Per Van's recommendation at the time, I relocated my "Ducati" R/R to the underside of the avionics tray. This has worked out fine so far.