Engine air with carb heat off?

[SSimpson77]

Sorry for the weird title but my question is this… Does the engine normally receive engine compartment air (unfiltered) when carb heat is off? Seems a bit weird to bring in hot unfiltered engine air while flying normally but that’s the way my carb heat/box works. Could this have been something a previous mechanic/owner did.

(The picture is with carb heat off and intake door open to receive filtered air from front, when I pull heat out, the box flap closes and the butterfly inside tube you see closes)

TIA

[ShuRugal]

That's the waste valve from carb heater, hot air flows out when carb heat not in use

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[Skates97]

This is a great writeup by Don Maxwell from back in the day.

 

CARB HEAT CARE.pdf

[DXB]

What the guys above said. Air that's picked up the carb/cabin heat air intake at the back right of the doghouse and pushed through the muffler shroud gets dumped overboard by the open butterfly valve when carb heat is not in use.  It's a weird system that can be tricky to maintain, but it sounds like yours is working correctly.  The system changed in '68 to take out the trouble-prone butterfly valve, as detailed in the article linked above.

[47U]

The D Max article doesn’t show a picture of the early model hot air dump duct… If you remove the screw that’s holding the cable clamp and install the proper sized duct, the clamp fits perfectly and no extra hardware is required.

[SSimpson77]

As always you guys come through awesome! Thank you all.