Cabin Heat is Lightly Smoking

ARFlyer

ARFlyer

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One of our 172Ns is having a slightly smoke whenever the cabin heat is applied. It's only occurring on the pilot side vent and the shroud looks intact. We took the cowling off and inspected the cabin heat hose and connections. Everything check out in good condition. Only thing we can think of at this point is some oil burning off the engine from a spill. Any ideas?
 
Where there's smoke there's fire. I certainly wouldn't fly it until the problem is resolved. Had a friend get burned very badly in a C172 due to an electrical fire.
 
Slightly smoking is like almost pregnant. If it's smoking it is either on fire or will be. I'd consider that a grounding condition until you determine the source and repair it. Last thing you want is an in-flight fire.
 
Or as a Brit friend of mine put it ... "The only time you can have too much fuel is when the bahstad's on fiah."

Jim
 
remove muffler shroud and inspect muffler.also inspect fire tube inside muffler
 
Oil, or a birds nest, or exhaust. You don't know until you strip the cowling, look at the scat tubing and do some troubleshooting. Obviously none of those things are good for continued flight.

Indiana_Pilot said:
That is somewhat scary.. I think CO2 should be on your mind..
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Unless you mixing fizzy drinks or firing a paintball gun I'd actually be more concerned about CO.
 
Anyone do any maintenance lately? Even wash it? Solvents and soap residue that gets intonthe muffler shroud pressure intakes can make some smoke when the muffler gets hot the first time. If the smoke is repeatable look into it. If only the first flight after maintenance? I'd worry less about it. Been there, done that.
 
Indiana_Pilot said:
That is somewhat scary.. I think CO2 should be on your mind..
Click to expand...

hotprops said:
remove muffler shroud and inspect muffler.also inspect fire tube inside muffler
Click to expand...

The muffler shroud came back good from when my student, an A&P, looked into it.

Stewartb said:
Anyone do any maintenance lately? Even wash it? Solvents and soap residue that gets intonthe muffler shroud pressure intakes can make some smoke when the muffler gets hot the first time. If the smoke is repeatable look into it. If only the first flight after maintenance? I'd worry less about it. Been there, done that.
Click to expand...

We are thinking that or someone split some oil which burned off next to the cabin intake. Nothing abnormal was found during the inspection and the 20 minute ground run didn't produce any additional smoke.
 
Did you lubricate the heater control flaps, hinges, cables, anything like that firewall forward? I lubed the heater control boxes in my Comanche once, and just after takeoff a bunch of smoke poured out of the heater vents. Scared the hell out of me, then I recognized the smell of LPS2. stopped as quick as it started, but it was exciting for a moment.
 
There is an airplane out there that 'doesn't" smell like burned oil when used for the first time in ages? News to me. In the KIng Air, with overhead electric heat, we'd joke that "at least it smells hot!!"
Don't get me going, it also had "supercharger" heat.
 
Yeah, may have to factor in if it's 'the 1st heat of the season'. Now real smoke isn't the norm, a little smell, temporarily, may not be as big a deal.

I'd keep some vents open as you evaluate. One would think it's checked well on each annual.
 
Maybe it's a Colorado, Nevada, California plane. I hear they like to smoke.
 
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