High CO in Cessna 150M Cabin

Mooney Fan

Mooney Fan

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Sep 17, 2017
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Mooney Fan
I'm getting high levels of Carbon Monoxide in my cabin. With all the air vents closed it reached ~200ppm on my digital meter. Opening the vents and leaning out the mixture it dropped to about 25ppm.

I returned to the field and need to sort this problem out before flying it again.

SCAT tubing all appears good. Of course, in the summer the the heater has not been used.

Last annual IA said my windshield seal was toast. Essentially, its not there. Could gases be coming in there?

Also, my gear leg fairings that cover the slots in the fuselage where the legs go through have gaps. Looks like some type of clear tape has been used to seal the gaps with some of it missing. Can exhaust gases come into the cabin through those slots?

Cabin door seals are new.

Where is the most common place CO comes into the cabin from?

Thanks for any suggestions.
 
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High CO2? I wouldn’t be worried at all. Now CO on the other hand…

:)
 
Mooney Fan said:
Also, my gear leg fairings that cover the slots in the fuselage where the legs go through have gaps. Looks like some type of clear tape has been used to seal the gaps with some of it missing. Can exhaust gases come into the cabin through those slots?
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It can, but with the 150s it's not a common problem. That leg goes into bushings in bulkheads in the gear box, and there is no real access to the cabin from the outboard end of the box where the first bushing is. That bushing would have to be shot to let CO past it.

More than likely is a cracked muffler. Even with the heat shut off there is still some leakage into the cabin through the heat valve, especially if it's not rigged right.

Canada, being a super-cold country where real pilots go flying even when the temperatures are near freezing:), has an AD that demands inspection of exhaust-type cabin heaters every 12 months/150 hours. I have found cracks. The AD starts with a visual inspection, with pressure and soap-testing of suspect areas, but I went to the soap right off. It revealed leaks that could not be seen. https://wwwapps.tc.gc.ca/Saf-Sec-Sur/2/cawis-swimn/AD_html.aspx?ad=CF-90-03&cn=CF&l=E
 
Why not try a trip around the pattern with cabin heat disconnected?

I’m presuming readings are fine on ground during taxi.

The boots around the steering rods just aft of the Firewall can cause this.

Assure ALL openings in the Firewall are sealed.
 
Man good luck with your investigation.

We had a similar issue in our Cherokee. Ended up with half a new exhaust stack. The slip joints were done as we just needed new pipes. Before the fix we’d get 30-50ppm when nose is up or after landing if winds are right. Now we never hear the monitor goes off.

When you look under the cowling, did you find any white/grey powder near exhaust bits? That was our clue.
 
Magman said:
Why not try a trip around the pattern with cabin heat disconnected?

I’m presuming readings are fine on ground during taxi.

The boots around the steering rods just aft of the Firewall can cause this.

Assure ALL openings in the Firewall are sealed.
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That's a good idea. I'll give it a go with the SCAT off the heater inlet.
 
SebIp said:
Man good luck with your investigation.

We had a similar issue in our Cherokee. Ended up with half a new exhaust stack. The slip joints were done as we just needed new pipes. Before the fix we’d get 30-50ppm when nose is up or after landing if winds are right. Now we never hear the monitor goes off.

When you look under the cowling, did you find any white/grey powder near exhaust bits? That was our clue.
Click to expand...
Not under the cowl. But I do have white near the tips of my exhaust that protrude through the cowl.
 
A little jb weld and it should last till next inspection.
 
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