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Smoke in Cockpit - Can It Be From the Oil Breather?

Pilotjim77

Well Known Member
I scared the c rap out of my girlfriend yesterday. We were getting ready to taxi to the runway, and the cockpit suddenly had an amount of smoke that was pretty noticeable. I thought it might be electrical, but wasn't sure. This was the first time this has happened since I bought the plane several weeks ago. I probably have about 10 hours of flying time in it. I shut down and put the airplane away pending investigation.

Today, I removed the cowl, and checked the engine compartment for any sign of fire. I also thoroughly checked under the panel for any evidence of fire. Nothing appeared burnt or charred. I got under the airplane, and I noticed that the exhaust pipe directly beneath the breather was coated with a significant amount of oil. The oil was not dripping onto the hangar floor, but the whole pipe was wet. I thought that the smoke probably came from oil burning off the exhaust pipe when the pipes started to heat up and finding it's way into the cockpit somehow, maybe through the cabin heat or the open canopy.

Should the oil breather be depositing oil after the engine stops running? This is the only way I can imagine it is got there. Any other ideas or thoughts?

Thanks in advance,

Jim
 
I wouldn't expect to get smoke in the cockpit from the oil dripping on the exhaust. Ask you girlfriend if the smoke had an acrid or sharp smell, a telltale sign of electrical fire.
 
With these responses, another thought just occurred to me. The right wing flap got jammed under the wing skin when I was raising the flaps prior to taxi. Could the flap motor be causing this problem?
 
The right wing flap got jammed under the wing skin when I was raising the flaps prior to taxi. Could the flap motor be causing this problem?

Yes it could Jim. Open the cover between the seats and thoroughly check the motor and wiring.
 
With these responses, another thought just occurred to me. The right wing flap got jammed under the wing skin when I was raising the flaps prior to taxi. Could the flap motor be causing this problem?

If the flaps were jammed and the motor continued to run for an extended period then it could overheat (although I've never heard of this happening), but if the flap switch is momentary in both directions like most are, then I would not expect the motor or wiring to overheat due to the momentary jam.
 
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If the flaps were jammed and the motor continued to run then it could overheat, but if the flap switch is momentary in both directions like most are, then I would not expect the motor to overheat due to the jam.

Walt couple years ago I was flying in a very cold temps for quite long. In the pattern at my destination I could not deploy flaps as usual the motor seemed very slow. It took three times longer to finally get full flaps (incrementally) but I did get a whiff of melted insulation.

Later inspection didn't show anything burned.
 
After you find your source of smoke

If your flaps jammed, as a second item to safety, have a CLOSE UP look at the weld where the flap arm joins the torque tube on the side that was jammed. You don't want to be on final and have one flap instantly retract if the weld let go.
 
Agree with all the responses. If you can't ID anything, I would still not takeoff. Get someone with a fire extinguisher, (that knows how to use it), as you power up electrical systems one by one. Maybe even do that first without the engine running that way you can maybe hear if somethings burning. Also the smoke won't be blown by the prop increasing your chances of perhaps seeing where the source is located.
 
Should the oil breather be depositing oil after the engine stops running? This is the only way I can imagine it is got there.

The breather line will have a fine mist of oil in the line and on the walls of the tube. I think it possible that this oil might continue to slowly drip out on to your exhaust after shut down. An air/oil separator would reduce the amount of oil that drips down. (Ensure you eliminate all other possible sources of the smoke first.)
 
With these responses, another thought just occurred to me. The right wing flap got jammed under the wing skin when I was raising the flaps prior to taxi. Could the flap motor be causing this problem?

So your right flap was jammed? Did you find out why? I know ist off-topic but still interesting to know what happened
 
So your right flap was jammed? Did you find out why? I know ist off-topic but still interesting to know what happened

Probably bumped the flap with my leg when it was fully extended during preflight inspection. I put some marks on the flaps now so as not to fully extend them on the ground.

Thanks for all the other responses. I still have not found the source of smoke. I'm getting a very faint odor of smoke after start up, but no visible smoke. I checked the flap motor and wiring... no sign of burning or melting. No wiring or connections beneath the panel look burnt or melted. Nothing feels hot. Sure wish I could locate the source.
 
Last suggestions for you Jim. If there was no visible smoke in the cockpit but a strong smell it could be exhaust gases. It happens very rare usually if you are idling while holding short and there is a slight tailwind. It comes via fresh air vents. Or descending at prolonged idle from high altitudes.
 
mine does this on rare occasions

My engine drips a bit of oil from here and there - kind of expected at 900+ hours. One time, that oil made its way onto an exhaust pipe, and into the heat muff. You can imagine the effect on start-up, as the cabin heat valve was open :eek:

Lots of smoke in the cockpit, but it cleared rapidly as the stain burned off.

Yes, I shut down and decowled to check things out.

Any more, I don't panic if I get a brief smell of burning oil on start-up, so long as it clears quickly. I never open the heat valve until the engine has been running for a few minutes on the ground. I can abide the odor, but not smoke in the cockpit. Part of learning the aircraft, I suppose. Keeping the engine wiped down every time the cowl is off goes a long way to mitigate this thankfully rare occurrence. I suspect your issue is similar.

With winter just around the corner, I will have to re-establish the habit of not opening the cabin heat too early in the start-up sequence.
 
If your breather is above a tailpipe I found, following Smokey Ray posts, that it did not allow enough flow out the breather.

That might make leaks and up consumption and mess. It is too high a pressure area in the lower cowl. Sounds like it has nothing to do with your smoke, but a breather that clears the lower cowl seems best. Especially when not using an air oil seperator.

I no longer have to wipe 1/2 teaspoon of oil off the belly aft of the breather each flight and no oil on the tailpipe. Cut it so there is a 45 degree slant, more open to the trailing side.

For freezing protection of your nose seal, make sure there is a whistle slot or relief slice near the highpoint of your breather line.
 
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The breather line will have a fine mist of oil in the line and on the walls of the tube. I think it possible that this oil might continue to slowly drip out on to your exhaust after shut down. An air/oil separator would reduce the amount of oil that drips down. (Ensure you eliminate all other possible sources of the smoke first.)

Oil will definitely drip out of the breather line after shut down / overnight.
 
Another possibility, oil from another gauge dripping on something electrical. Here's a local incident report with exactly that situation:

Update TSB #A19P0091: C-GMZA, a Cessna 152 aircraft operated by Canadian Flight Centre, was conducting a local training flight from Vancouver/Boundary Bay (CZBB), BC with a student-pilot and an instructor on board. During the initial climb after the takeoff, smoke was observed coming from under the instrument panel, near the electrical switches. The instructor assumed control of the aircraft, reduced the power, turned off the master switch, and closed the cabin air. The smoke subsided, and the instructor turned the aircraft toward CZBB for a landing. The instructor momentarily selected the master switch to on, communicated a MAYDAY, and re-selected the master switch to off. The aircraft landed and taxied to the ramp. The instructor advised that emergency vehicles were not required. The operator's maintenance found a leak from the oil pressure gauge located above the switch panel, with traces of oil on the landing light switch. The gauge cluster was replaced. There were no signs of electrical fire on the electrical wiring under the dash. dditionally, minor oil spillage was found around the engine oil filler tube. The aircraft was returned to service.
 
Another possibility, oil from another gauge dripping on something electrical. Here's a local incident report with exactly that situation:

Interesting ... but where did the smoke come from? Oil is not generally very conductive, so it's not likely to be an oil generated short. Something else would have to be hot to generate the smoke .. quite hot! Not sure this incident was properly root caused...
 
My engine drips a bit of oil from here and there - kind of expected at 900+ hours. One time, that oil made its way onto an exhaust pipe, and into the heat muff. You can imagine the effect on start-up, as the cabin heat valve was open :eek:

Lots of smoke in the cockpit, but it cleared rapidly as the stain burned off.

Yes, I shut down and decowled to check things out.

Any more, I don't panic if I get a brief smell of burning oil on start-up, so long as it clears quickly. I never open the heat valve until the engine has been running for a few minutes on the ground. I can abide the odor, but not smoke in the cockpit. Part of learning the aircraft, I suppose. Keeping the engine wiped down every time the cowl is off goes a long way to mitigate this thankfully rare occurrence. I suspect your issue is similar.

With winter just around the corner, I will have to re-establish the habit of not opening the cabin heat too early in the start-up sequence.

I have checked every electric wire and connection closely and can't find anything. The flap motor wiring looks fine, and the flaps are working with no problems. Turning on all electrical components before startup does not produce any smoke or smell.

I am still getting the smell of smoke shortly after startup with the canopy slightly open, and I'm thinking it's got to be oil from the exhaust. It lasts less than 30 seconds then goes away.
 
I have checked every electric wire and connection closely and can't find anything. The flap motor wiring looks fine, and the flaps are working with no problems. Turning on all electrical components before startup does not produce any smoke or smell.

I am still getting the smell of smoke shortly after startup with the canopy slightly open, and I'm thinking it's got to be oil from the exhaust. It lasts less than 30 seconds then goes away.

Next time bring along a buddy who works on cars. Burning oil has a pretty unique smell and will be easily identified by someone familiar with it.

Larry
 
Another Possibility?

Had a somewhat similar (but perhaps less in magnitude) experience in the midst of addressing starting issues. Would occasionally, but not every time, get an odd hot/burnt/etc. odor on startup.

Turns out that under heavier loads (e.g., when the system was recharging the battery after a challenging start) the alternator belt was "slipping" (to use an auto term) a little bit. Inspected/adjusted the belt tension, and no more intermittent odor...
 
One idea

Give the flap motor a good strong whiff, with your nose right up on it.

Does it smell like your smoky cockpit did?

I think the motor can get a little burned inside but still operate. This might have happened during the time that your flap was jammed.

Probably bumped the flap with my leg when it was fully extended during preflight inspection. I put some marks on the flaps now so as not to fully extend them on the ground.

Thanks for all the other responses. I still have not found the source of smoke. I'm getting a very faint odor of smoke after start up, but no visible smoke. I checked the flap motor and wiring... no sign of burning or melting. No wiring or connections beneath the panel look burnt or melted. Nothing feels hot. Sure wish I could locate the source.
 
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