CO in the cockpit

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Mtns2Skies

Final Approach
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Mtns2Skies
My CO detector tells me I've got about 40 PPM in the cockpit during climb/cruise. If I turn air or heat on it will drop significantly. I have all new window/door seals and my plane is equipped with anti-CO scoops to pressurize the tail and prevent CO from entering from the tailcone.

So where should I be checking? Firewall leaks?
 
Are you sure the CO detector is accurate?
 
Well I'll be darned...a pressurized Cessna 180. And I thought I was going to have to spring for at least a Malibu to get that. :D

More seriously, try taping off the normal fresh air and heater inlets and then run a test flight to see if it makes a difference. Those, when closed and air flow is minimal, are often the culprit.
 
Add a seaplane tailpipe extension.

Make sure the source isn’t from your muffler shroud. Cracks at the tailpipe-muffler weld are fairly common. So are leaky clamp joints if that's what your exhaust uses.
 
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Mtns2Skies said:
Yeah, I replaced those with new when I bought the plane. They're holding up fine.
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How tight are they? The one on the right side is critical, being right behind the exhaust stack, and in the climb the AOA drags exhaust past it.
 
What does the methane detector say? LOL

af1bd945185756063e468cd581a5826e.jpg
 
Sorry if I missed it..What kind of airplane??
 
My 150 is likely getting its small amount of CO (9-10 ppm) from the (very) leaky door bottom seals. I found out because the CO goes completely away with Cabin Heat on, and comes back when it is off. This is assuming that the fresh air vents are also closed.

Lots of different sources of CO entry. We have a brand new exhaust and muffler on the cabin heat side, so all good there. And new steering boots, but very bad door seals. However, if it never goes above 10 ppm, we probably won’t be rushing to fix it.
 
Our O470 (182P) has went as high as 20ppm or so during a runup. On taxi and take off maybe 3...7. But once into climb and cruise I've never seen it over 2ppm.

I would take it serious. Obviously the 40ppm has a pretty long term range but seeing 40ppm during cruise would really have me concerned.

This is measured with a SensorCon mounted on the panel.
 
If was a lot closer I'd happily let you take ours up so you could have 2 to compare.
 
Being more serious than earlier...

I’m surprised it doesn’t change between climb and cruise. Might indicate something about the source. Not quite sure what though.

The internetz say that level is unlikely to even cause symptoms in ground pounder life, but I’m wondering what the sciencey types would say a safe level is for us aeronautical nuts.

I suspect it’s difficult to get all spamcans to zero. Too many leaks.
 
Unrelated trivia ..... many years ago the auto industry solved the problem by slightly pressurizing the cabin with fresh incoming air so that nothing could enter via poor seals or leaks ... they do it by running the heater-AC fan at a very low setting even though the fan is switched off... easy to do in a car because new air enters from the cowl area just under the windshield ....

I am not familiar with Cessna incoming air source ... but if you are certain no gases enter there I would just leave the fan at lowest setting for best air quality

Here is the thing .... a moving aircraft or auto creates a slight vacuum in the cabin ... thus replacement air tries to come in wherever it can ... a low fan pushing fresh air halts all the other sources.

Just like if you are driving your car and crack a window just a bit is the worst thing because the cabin vacuum rises significantly . Sounds counter-intuitive but true .... using slightly pressurized fresh air causes cabin air to exit thru old seals and leaks ... and that is ideal
 
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Mtns2Skies said:
My CO detector tells me I've got about 40 PPM in the cockpit during climb/cruise. If I turn air or heat on it will drop significantly. I have all new window/door seals and my plane is equipped with anti-CO scoops to pressurize the tail and prevent CO from entering from the tailcone.

So where should I be checking? Firewall leaks?
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See my post above .... if it was me I would always leave the fan on the lowest setting .... even if all the seals were new etc ... and like I said , there is a "natural vacuum" in your cabin as soon as you are moving and foul air will try to come in wherever it can so use the fan to halt it. Best wishes.
 
A Martin said:
I am not familiar with Cessna incoming air source ... but if you are certain no gases enter there I would just leave the fan at lowest setting for best air quality
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Fan?
 
dmspilot said:
Fan?
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As in heater/AC fan .... unless Cessna has neither .... I am from the dark side of aviation (helicopters) ... also an auto-tech , also an air-makeup tech for buildings & enclosures etc.
 
To clear things up, the OP has a 180. Like most Cessnas the heat control is a temp controller only. To make heat flow you need to pull the fresh air knob, too. He needs to inspect the muffler asap.
 
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A Martin said:
As in heater/AC fan .... unless Cessna has neither .... I am from the dark side of aviation (helicopters) ... also an auto-tech , also an air-makeup tech for buildings & enclosures etc.
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Just the giant AvGas powered one in the front ;)

Interesting post nonetheless about how the issue has been addressed in cars.
 
Stewartb said:
To clear things up, the OP has a 180. Like most Cessnas the heat control is a temp controller only. To make heat flow you need to pull the fresh air knob, too. He needs to inspect the muffler asap.
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thanks .... the OP said.... "If I turn air or heat on it will drop significantly" .... thus I think electric fan .

Pulling the fresh air knob should accomplish the same thing if the aircraft is moving ... I am assuming it truly draws in fresh air ..... I still am curious where the intake is located.
 
wanttaja said:
Hay-El, I can't get my open-cockpit airplane to zero. Wouldn't expect closed-cabin planes would be any better....
View attachment 95421
Ron Wanttaja
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Believe it or not an open cockpit could be hardest to feed with fresh air ..... exhaust pouring out behind a propeller which swirls all around your open cockpit.

Just like the old farm tractors before they had cabs .... operator sits 4 feet behind the exhaust stack and breathes it all day.
 
Stewartb said:
Hell, denver-used to be a pilot is the smartest guy in the room. Let’s wait.
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I see being called out on your inaccurate aerodynamics assertions ruffled you so much you decided to start in with personal insults instead of acknowledging you made a mistake.

Pretty common.

As usual I’ve made no personal insults.

I’m no brilliant guy, I’ve had my ass handed to me here and acknowledged it. It’s not that hard. Or a big deal, since it’s why we’re all here.

A couple people here really upped my game in a few areas. I said dumb things and they explained why they were dumb with hard facts.

Welcome to the club. It isn’t personal. If I hadn’t said it, someone else would have. It doesn’t take long around here, which is a good thing really.

Old wives tales and all sorts of aviation misconceptions come here to die. Everybody posts one eventually.
 
Stewartb said:
He needs to inspect the muffler asap.
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Muffler was inspected at annual a couple months ago and this problem didn't suddenly develop. The exhaust system was also replaced two years ago. The reason I don't think it's heat exchanger related is that the CO goes down when I turn on heat, so it must be getting into the cabin somewhere else.
 
GRG55 said:
Cessna 180.
But then all those high-wing, strut-braced Cessnas look the same. :D

(ducks to avoid heavy airborne projectiles)
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What confuses me is they are both called a sky wagon, no?
 
check for leaks in the tail cone....tail area.
Mtns2Skies said:
Muffler was inspected at annual a couple months ago and this problem didn't suddenly develop. The exhaust system was also replaced two years ago. The reason I don't think it's heat exchanger related is that the CO goes down when I turn on heat, so it must be getting into the cabin somewhere else.
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NealRomeoGolf said:
What confuses me is they are both called a sky wagon, no?
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So are Cessna 205/206/207's of certain years. It's just a marketing name that 180/185's claimed for themselves. Mine is actually a 'true' Skywagon since that's the marketing name Cessna had going at the time of manufacture.

Similar to 'business liner' which was all 170/190/195's of the day.
 
Mtns2Skies said:
So are Cessna 205/206/207's of certain years. It's just a marketing name that 180/185's claimed for themselves. Mine is actually a 'true' Skywagon since that's the marketing name Cessna had going at the time of manufacture.

Similar to 'business liner' which was all 170/190/195's of the day.
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I guess I can’t complain with half the Pipers, mine included, called a Cherokee. Mine’s officially a Cherokee Lance.
 
Mtns2Skies said:
Muffler was inspected at annual a couple months ago and this problem didn't suddenly develop. The exhaust system was also replaced two years ago. The reason I don't think it's heat exchanger related is that the CO goes down when I turn on heat, so it must be getting into the cabin somewhere else.
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Same thing happens in my 150. And I too have a new muffler on the cabin heat side. But my door vents are so bad that my left leg gets cold in the winter, so that is obvious in my plane.

FYI for others - Cessna fresh air vents are often located high up on the wings, far away from the exhaust and are powered by airflow, not fans.
 
Matthew Rogers said:
FYI for others - Cessna fresh air vents are often located high up on the wings, far away from the exhaust and are powered by airflow, not fans.
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That's the cold air. The cabin heat air comes off an outlet on one of the engines cooling baffles, through some SCAT hose to the shroud around the muffler, through another SCAT to the heat valve, which either directs it to the cabin or dumps it overboard. The overboard provision is to keep the muffler from overheating and burning out; got to keep that air moving.

So both the cool air and heated air are fan-powered. That big, noisy fan on the front of the airplane.
 
All Cessna heat does is route heat from the muffler shroud into the air plenum. An air scoop on the side of the plane pressurizes the plenum. You can get some flow from just the muffler but the way to get it moving faster is to use the air control and heat control together.
 
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