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Exhaust fumes in cabin

ozone

Registered User
Calabogie, Ontario
I recently got my PA-12 floatplane flying after a 5.5 year rebuild. It has an o320 150hp with pa-18 exhaust. Very impressed with performance and it flys great.

The only issue I’m having is it’s getting exhaust in the cabin from outside. I’m guessing due to the low pressure in cabin. I’ve sealed up the door, plugged off the cabin heat and tried extending the tail pipe 4”. None of this has helped.

The only thing left I can think of is somehow sealing off the front gear fitting area and plugging the drains under the fuselage. The wing root fairings are not completely sealed but I don’t see how it would get through there.

Anyone else have an issue similar to this?

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Can come in through the tail openings. Near the spring attach and trim slots. Stick some CO detector cards nearby to check for local source that darkens them quick.

Gary
 
Muffler crack? They are not always obvious or easy to find. Pull the SCAT hose off the cabin air box and look for tan-grey deposits, or block it and see if the problem clears up. My 12 got through two annuals with a crack that no one could locate until we noticed that. I believe that the stock PA18 muffler has a 100 hour inspection requirement. I replaced mine with an FA Dodge HD muffler which eliminated that.
 
Is fuselage tail open at tail post? Can create vacuum in fuselage. Plug it with a piece of foam. And retest.


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Are you certain it's exhaust? Are you using a carbon monoxide detecter? New planes make lots of smells, many that could be mistaken for exhaust.
 
Are you certain it's exhaust? Are you using a carbon monoxide detecter? New planes make lots of smells, many that could be mistaken for exhaust.

Theres potential for lots of smells on a new build creeping in the cabin - oil burning off hot surfaces, cylinder paint etc. I would second the co2 detector method
Good looking plane, congratulations!
 
Definitely test with a CO detector (not the little card, a digital one) before you do anything else. In the right winds, my 180 will get a little CO in the cabin but nothing near the unhealthy point.

Here is a test I did a while back.. https://youtu.be/8hYWKRd4NG8 Be sure it is a current device...

sj
 
Is the fuselage totally sealed up next to the tailwheel? Some cubs have extra bracing there and a small opening. Exhaust gases will penetrate into the cabin via that opening.
 
I tracked down some CO problems in my PA18 using a small digital CO detector.

I had some pretty high readings, in the 25 ppm range, on climb out. I plugged everything I could think of: door seals, baggage door hinge, gaps behind the baggage compartment, floor gaps, even the gaps around the brake lines on the bottom of the boot cowl.

I got a big improvement, and much less draft on the passenger, but I would still occasionally get 9-11 ppm on climb out (this sensor won't read lower than 9 ppm).

It turns out that the problem is related to the left sliding window. If the window is completely closed or open more than a few inches - no problem. However, if the window is cracked, say 1/4", then the problem occurs. Apparently, the small crack creates a big vacuum in the fuselage, bringing in exhaust from the remaining small gaps (that I can't find).

Hope this helps.

Here is the detector:
https://www.amazon.com/gp/product/B076S6KBP2/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
 
Have opening in rear fuselage bottom. I was getting fumes entering the front side of the cover. Price of foam seal stopped it.
 
Thanks everyone for the tips and help.

I ended up sticking foam in every crevice I could find. This seemed to fix the issue. I then removed a bit every flight. After removing the foam around the fwd gear fittings I got lots of fumes back in the cabin.
With the lower pressure in the cabin it must have been sucking it in around that opening and coming up through the floor. And like Steve was saying it does get worse if I crack the window a bit probably due to the vacuum effect.

Definitely nice to get rid of that issue. Makes flying it a lot more pleasurable now.
I’ll probably also invest in one of those digital CO meters. Seems like good insurance.




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