How much CO is too much?

benyflyguy

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benyflyguy
IMG_8379.jpegIMG_8380.jpegIMG_8381.jpegplane is a Cessna 182H with O470. Couple of years ago after being a bit more fatigued after a flight I purchased a sensorcon CO detector. Was seeing 30 by me and higher in back. Thought it was a bad seal. They sealed doors and was about the same. Went in for annual and found cracks in the exhaust manifold. So it was replaced. And the numbers went down. Zero to Low singles less then 5. I fly with it Everytime. Well I noticed the other day the numbers seemed to climb. Need to experiment more. Vents open in front readings 8-10. But in back readings jumped 15-28. Now I think my sensorcon might be past date. So I’m ordering a new one. But anything I can test to troubleshoot. I think on ground idle was zero oe very low and on climbout was low as well. Levels seem to go up with level flight.
 
CO sensors are a life-limited part, though I've no idea what the service life might be for the sensor you have.

But kudos for being all over this, with testing and repairs. Too many people have no idea it's a problem until it's too late.
 
The Sesnorcon will tell you when it's out of date. I forget the exact annunciation, but mine went past date and I sent back to be recalibrated.
Think they are pretty accurate. You've got CO, not an indicator issue.
 
Thanks. I think I have to set up a sheet and try with some different factors. Talk to mechanic first
Climb/level/descent
Changes with cowl flaps
Vents
Cabin air open or closed.
 
These electrometric detectors eventually deplete their electrolyte. They typically last about 5-10 years. Mine (Forensic Detectors) has an expiration date printed on the back. Others (like sealed home units) may provide an expiration date message on their screen when they reach EOL. It is possible they will die before then, but that usually means they do not respond at all. You should not see any CO in the cockpit during flight. You MIGHT see small quantities of CO on the ground with the canopy/windows open due to exhaust gas ingress into the cockpit. Presence of CO inside the cabin in flight is an indication of exhaust gas ingress somewhere. What happens when you open the cabin heat knob?
 
Yeah, I'd have someone take another look at your exhaust system. My plane was purchased with a relatively recent new exhaust system installed. I noticed that I was feeling unusually fatigued after flying but the little dot on the sticky CO detector looked OK (obviously not a precise instrument!). I happened to purchase a second headset for my wife to use (Lightspeed Delta Zulu) which has a built-in CO detector. It was fine on the ground, but in a climb it started squawking at me about increased CO. Seemed to resolve again in level flight, but it was definitely heading in the direction of triple digits during climbs and slow-flight practice. Turns out that whatever yahoo installed the exhaust system decided to use some non-appropriate sealant. My mechanic figured this out during the first annual and was nearly throwing things in frustration.

The values you're showing are suboptimal but not concerning for incapacitation. Doesn't mean the problem can't get suddenly worse though, so probably worth your while to at least have someone take a close look at the usual suspects.
 
View attachment 133689View attachment 133690View attachment 133691plane is a Cessna 182H with O470. Couple of years ago after being a bit more fatigued after a flight I purchased a sensorcon CO detector. Was seeing 30 by me and higher in back. Thought it was a bad seal. They sealed doors and was about the same. Went in for annual and found cracks in the exhaust manifold. So it was replaced. And the numbers went down. Zero to Low singles less then 5. I fly with it Everytime. Well I noticed the other day the numbers seemed to climb. Need to experiment more. Vents open in front readings 8-10. But in back readings jumped 15-28. Now I think my sensorcon might be past date. So I’m ordering a new one. But anything I can test to troubleshoot. I think on ground idle was zero oe very low and on climbout was low as well. Levels seem to go up with level flight.
Sensorcon will recertify your device. I think the cost is less than a new one, but you should check to be sure.

FWIW, I recently replaced my engine in my 182K, and the CO readings were unacceptably high (they were much lower with the old engine). The working theory was that once the exhaust system was removed, the jostling caused rust and/or corrosion in the exhaust system to work loose, thereby letting more CO escape. The mechanic also thought that running the new engine richer during break-in contributed to the high CO readings. Regardless of the reason, the CO level was too high. We tried replacing just the clamps, but that didn't improve things. So, I replaced the entire exhaust system with AWI components, and the CO readings went from unacceptable to almost non-existent.

If your exhaust system is original to the plane, it's older than mine was. It may be time to bite the bullet and get a new exhaust.

YMMV.
 
The question is how long does it take to synthesize the CO? And since it displaces red blood cells that carry oxygen….breathing oxygen may not help.
 
The question is how long does it take to synthesize the CO? And since it displaces red blood cells that carry oxygen….breathing oxygen may not help.
It gets "synthesized" right away in the engine. It doesn't displace any cells but it binds to hemoglobin- it has 200 - 300x the affinity for hemoglobin compared to oxygen. It also interferes with various cellular processes. Actually, 100% oxygen is a treatment after removing the person from the contaminated atmosphere. It's not a covalent bond to hemoglobin so CO will slowly leave the body. @bbchien please correct me if needed!
 
Need a critical care respiratory therapist here...
 
The question is how long does it take to synthesize the CO? And since it displaces red blood cells that carry oxygen….breathing oxygen may not help.
The half life of CO in carboxyhemoglobin is several hours. That can be reduced to about an hour in 100% oxygen. CO not only ties up hemoglobin by binding to it (around 200x tighter than oxygen), it also dramatically alters the O2 delivery efficiency of the remaining, uncontaminated hemoglobin. The most effective treatment is to allow the CO gradually dissociate from your hemoglobin, and 100% oxygen can speed that up.
 
One thing, running LOP reduces the production of CO in the engine. :)
 
The muffler, if it's used for cabin heat, needs pressure-checking. Use a clean-out shop vac for the air, and soapy water for the bubble checking. Lots of soap. Too much pressure will blow the soap away and no bubbles will be noted. This will find tiny, invisible cracks.

The main gear legs might need sealing up at the fuselage. Common entry point for exhaust in flat-leaf leg airplanes.
 
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