CO mystery - any ideas?

[Andrew Gideon]

Our Cessna R182 is getting CO in the cockpit. We've now had three different
shops look at it multiple times, all to no (complete) effect. They've done
things like resealing the firewall, the gear-wells, the exhaust, and the
like. But still we get CO.

We've swapped CO detectors around between planes, so the detectors' results
are trusted.

One interesting oddity: turning cabin heat on does seem to get rid of the
CO.

We've noticed no difference made between type of flight. I personally have
had readings both while XC and while maneuvering (practicing commercial
maneuvers), and at various altitudes. Others have reported the same.

At this point, we're at something of a loss. The next thing we're trying is
to extend the exhaust pipe. The presumption is that this would get the CO
into the slipstream and away. But that "presumption" is really more of a
"guess" or even a "hope".

Anyone have any suggestions or ideas or experiences that might help us?

Thanks...

Andrew

[[email protected]]

Andrew Gideon > wrote:
> Our Cessna R182 is getting CO in the cockpit. We've now had three different
> shops look at it multiple times, all to no (complete) effect. They've done
> things like resealing the firewall, the gear-wells, the exhaust, and the
> like. But still we get CO.

> We've swapped CO detectors around between planes, so the detectors' results
> are trusted.

> One interesting oddity: turning cabin heat on does seem to get rid of the
> CO.

> We've noticed no difference made between type of flight. I personally have
> had readings both while XC and while maneuvering (practicing commercial
> maneuvers), and at various altitudes. Others have reported the same.

> At this point, we're at something of a loss. The next thing we're trying is
> to extend the exhaust pipe. The presumption is that this would get the CO
> into the slipstream and away. But that "presumption" is really more of a
> "guess" or even a "hope".

> Anyone have any suggestions or ideas or experiences that might help us?

> Thanks...

> Andrew

Is the exhaust stack somehow different than the stacks on the hundreds of
other 182s that don't have this problem?

If it is the same, look elsewhere.

--
Jim Pennino

Remove -spam-sux to reply.

[Ron Wanttaja]

On Sat, 06 Nov 2004 20:05:19 -0500, Andrew Gideon > wrote:

>Our Cessna R182 is getting CO in the cockpit. We've now had three different
>shops look at it multiple times, all to no (complete) effect. They've done
>things like resealing the firewall, the gear-wells, the exhaust, and the
>like. But still we get CO.
>
>We've swapped CO detectors around between planes, so the detectors' results
>are trusted.
>
>One interesting oddity: turning cabin heat on does seem to get rid of the
>CO.

It slightly pressurizes the cockpit, hence the cockpit is less likely to pull in
exhaust gasses.

I've heard that Cessnas often pull the CO in *from the tail*. The cockpit,
being normally a low-pressure area, sucks the CO from the tail to the cabin.
I'd take a look at holes in the fuselage aft of the cabin. If there aren't any
obvious gaps, seal the inspection panels, etc. with tape and see if the amount
changes.

Ron Wanttaja

[David Herman]

"Andrew Gideon" > wrote in message
online.com...
> Our Cessna R182 is getting CO in the cockpit.

How do you know - what sort of gizmo are you using to test (some are quite
accurate, others ain't)?

How much CO are you getting? Is it more than other airplanes? Is it enough
to worry about?

Where within the cabin are you taking your readings? Are you taking
readings at different locations in the cabin, and under different flight
configurations?

I ask these questions because I suspect *all* GA aircraft have at least some
CO in their cockpits.

I bought one of the CO Experts digital CO monitors about a year ago, and
some of what it seems to be saying surprised me.

At least in my plane (an old C-150 with typically drafty windows) the more I
open up the vents (and to some extent, the windows), the more CO seems to be
present in the cockpit - which was exactly the opposite of what I expected.
If I close everything up tight (or as snug and things get), the CO meter
shows a low level (although it does vary a bit depending of power settings,
climb/descent/cruise, and even which way the plane is turning; it also
varies significantly depending on where in the cabin it is).

I've come to the following tentative conclusions:

1. There's always at least a little CO in the plane if the engine is
running; the unit it quite sensative.
2. I'm not getting a significant amount of CO through the firewall or
aircraft structure.
3. Most, if not all, the CO in the cockpit seems to be coming in from
outside, probably mostly leaking in around the windows, and coming in
through the cessna soup-can vents at the wing roots.
4. Under most configurations, the CO level is nice and low. The worst
configuration seems to be full power, in a climbing right turn (to my
surprise, the turn direction made a significant difference) with all the
vents open - under that config the CO level climbs somewhat, but I rarely
fly in that configuration for extended periods.
5. Experimenting with the CO monitor in different locations throughout the
cabin produced more surprises: the further forward I placed the monitor, the
lower the CO levels were. I expected the highest readings would be at knee
level or foot level, close to the firewall. Nope. That's where the lowest
levels were. The highest levels were behind the seats, just aft of the
window frames (where I suspect most of the CO is coming in). I considered
this good news since the levels near my head - where the air I'm breathing
is - were among the lowest.

I'm sure it's different for every airplane, but at least in mine, the
results were surprising but ultimately reassuring. Now I leave the CO
monitor on the "hat shelf" behind the baggage area behind the seats, about
24-30 inches behind my shoulders. It chirps regularly in flight (indicating
a low level of CO). Nice to have, for a hundred bucks it provides a lot of
peace of mind: I do *not* worry at all about CO killing me (lots of other
things still to worry about, but I get to cross CO of my list, as long as I
hear that periodic chirp from the CO monitor from behind the seats). How
many other worries can you pretty much completely eliminate for a hundred
bucks?

Hope that helps a bit.


David Herman
N6170T 1965 Cessna 150E
Boeing Field (BFI), Seattle, WA
- - - - - - - - - - - - - - - - - - - - - - - - - -
Visit the Pacific Northwest Flying Forum:
http://www.pacificnorthwestflying.com/

[Roger Long]

We have the same detector in our 172 N and I have never seen any CO even
though we have doors that don't fit very well. The memory function
sometimes shows a zero hour, 30 - 40 peak from startup but that's all we've
seen in two years.

I and several other club members run the engine slightly LOP. (Yes, you
actually can do this with a simple engine if the induction system is tight
and the ignition system is good.) One advantage of this is minimal CO
production.

--

Roger Long

[Roger Long]

We have a 172 with leaky door seals and we never get CO. Here's my guess:

The exhaust stack will usually get the discharge far enough from the plane
that gas will not be sucked back in. Even if the firewall is tight, exhaust
gas in the engine compartment will leak slowly out around the aft edge of
the cowl and mix with the flow very close to the fuselage skin. From there,
it will be sucked in every opening, even at the tail.

I would guess that you still have an exhaust leak somewhere in the engine
compartment.

Try putting one of the Aeromedic detector units with memory function under
the cowl for a flight and see what it tells you. You might need to
pressurize the engine with a shop vac and bubble test everything. If the
leak is effected by temperature, as many are, that still might not find it.

Do you see a difference in readings with cowl flaps open and flaps closed?

--

Roger Long



"Andrew Gideon" > wrote in message
online.com...
> Our Cessna R182 is getting CO in the cockpit. We've now had three
> different
> shops look at it multiple times, all to no (complete) effect. They've
> done
> things like resealing the firewall, the gear-wells, the exhaust, and the
> like. But still we get CO.
>
> We've swapped CO detectors around between planes, so the detectors'
> results
> are trusted.
>
> One interesting oddity: turning cabin heat on does seem to get rid of the
> CO.
>
> We've noticed no difference made between type of flight. I personally
> have
> had readings both while XC and while maneuvering (practicing commercial
> maneuvers), and at various altitudes. Others have reported the same.
>
> At this point, we're at something of a loss. The next thing we're trying
> is
> to extend the exhaust pipe. The presumption is that this would get the CO
> into the slipstream and away. But that "presumption" is really more of a
> "guess" or even a "hope".
>
> Anyone have any suggestions or ideas or experiences that might help us?
>
> Thanks...
>
> Andrew
>

[Andrew Gideon]

David Herman wrote:

> How do you know - what sort of gizmo are you using to test (some are quite
> accurate, others ain't)?

I forget the make/model, but I'll get that when I'm next at the airport.

> How much CO are you getting? Is it more than other airplanes? Is it
> enough to worry about?

Our club has four aircraft: a straight-leg 182 and two (180HP modified) 172s
(an N and a P). Swapping detectors around yields zero consistently in the
other aircraft, and nonzero readings in the R182. I don't recall the
numbers, but there were not in the "you're about to die" range but they
were in the "you should do something" range (judging from the documentation
of the detector {8^).

> Where within the cabin are you taking your readings? Are you taking
> readings at different locations in the cabin, and under different flight
> configurations?

All over, yes, and yes. I myself flew one of the "stick the detector
somewhere to see what happens" flights. We've been unable to discern a
pattern, although there does appear to be a slight increase in the
passenger seats vs. the front seats. Maybe. I've always assigned this to
the fact that the air vents are in front, and the difference is slight
anyway.

[...]
> 3. Most, if not all, the CO in the cockpit seems to be coming in from
> outside, probably mostly leaking in around the windows, and coming in
> through the cessna soup-can vents at the wing roots.

When I open those vents, the numbers appear to go down.

[...]

> Hope that helps a bit.

I'm sorry, but - at least with our detectors - the fact that the other
aircraft show zero does imply an issue here. We may have less sensitive
detectors than you.

- Andrew

[[email protected]]

Andrew Gideon wrote:
> Our Cessna R182 is getting CO in the cockpit. We've now had three
different
> shops look at it multiple times, all to no (complete) effect.
They've done
> things like resealing the firewall, the gear-wells, the exhaust, and
the
> like. But still we get CO.
>
> We've swapped CO detectors around between planes, so the detectors'
results
> are trusted.
>
> One interesting oddity: turning cabin heat on does seem to get rid of
the
> CO.
>
> We've noticed no difference made between type of flight. I
personally have
> had readings both while XC and while maneuvering (practicing
commercial
> maneuvers), and at various altitudes. Others have reported the same.
>
> At this point, we're at something of a loss. The next thing we're
trying is
> to extend the exhaust pipe. The presumption is that this would get
the CO
> into the slipstream and away. But that "presumption" is really more
of a
> "guess" or even a "hope".
>
> Anyone have any suggestions or ideas or experiences that might help
us?
>
> Thanks...
>
> Andrew

[Bruce Cunningham]

Andrew Gideon > wrote in message e.com>...
> Our Cessna R182 is getting CO in the cockpit. We've now had three different
> shops look at it multiple times, all to no (complete) effect. They've done
> things like resealing the firewall, the gear-wells, the exhaust, and the
> like. But still we get CO.
>
> We've swapped CO detectors around between planes, so the detectors' results
> are trusted.
>
> One interesting oddity: turning cabin heat on does seem to get rid of the
> CO.
>
> We've noticed no difference made between type of flight. I personally have
> had readings both while XC and while maneuvering (practicing commercial
> maneuvers), and at various altitudes. Others have reported the same.
>
> At this point, we're at something of a loss. The next thing we're trying is
> to extend the exhaust pipe. The presumption is that this would get the CO
> into the slipstream and away. But that "presumption" is really more of a
> "guess" or even a "hope".
>
> Anyone have any suggestions or ideas or experiences that might help us?
>
> Thanks...
>
> Andrew

The poster that said that pressurizing the cabin with the cabin heat
was what lowered the level of CO was probably correct. Cardinal RG's
have this problem and the cure is sometimes that in the rear
inspection covers on the sides of the tail in front of the stabilator,
they have a edge bent outward to scoop air into the tail and keep
exhaust out. These scoops or inspection plates have to be mounted with
the scoop facing forward so that they face the airstream. People have
installed the covers with the scoop facing down or backwards, usually
after an annual etc., and then they start getting CO in the cabin.
Check to see if your plane has this feature. I think it is common to
several Cessnas. If the scoops are not facing forward, I bet that is
your problem.

Bruce Cunningham
N30464

[PaulH]

In my Arrow, the normal cabin air flow is in through the vents, out
through an exhaust duct mounted on the bottom of the cabin. However,
when I had a bad door seal, the suction around the door from the low
pressure above the wing reversed the flow when I had vents closed and
heater on low: in through the exhaust duct, out through the door.

Not sure whether this could happen with a Cessna, but I suspect it
could.

[Andrew Gideon]

Bruce Cunningham wrote:

> the cure is sometimes that in the rear
> inspection covers on the sides of the tail in front of the stabilator,
> they have a edge bent outward to scoop air into the tail and keep
> exhaust out. These scoops or inspection plates have to be mounted with
> the scoop facing forward so that they face the airstream. People have
> installed the covers with the scoop facing down or backwards, usually
> after an annual etc., and then they start getting CO in the cabin.

Are these the round inspection plates like those one finds all over the
airplane, or something different?

Is the "scoop" really noticable, or a slight bending?

- Andrew

[Bruce Cunningham]

Andrew Gideon > wrote in message e.com>...
> Bruce Cunningham wrote:
>
> > the cure is sometimes that in the rear
> > inspection covers on the sides of the tail in front of the stabilator,
> > they have a edge bent outward to scoop air into the tail and keep
> > exhaust out. These scoops or inspection plates have to be mounted with
> > the scoop facing forward so that they face the airstream. People have
> > installed the covers with the scoop facing down or backwards, usually
> > after an annual etc., and then they start getting CO in the cabin.
>
> Are these the round inspection plates like those one finds all over the
> airplane, or something different?
>
> Is the "scoop" really noticable, or a slight bending?
>
> - Andrew

Yes they are. They are a combination scoop/inspection cover. The scoop
is about a 1/4 inch high outward joggle of the inspection plate just
in front of the stabilator. The open part must face the airstream,
that is, forward. There is one on each side. I don't know if 182s have
this. I think maybe some 210s do. If your plane is supposed to have
them and doesn't, in all likelyhood that is the problem. The scoop is
a Cessna part and can be ordered. It was the fix Cessna found when CO
was an issue on the Cardinal RG, maybe other models. My fixed gear
Cardinal does not have them. The exhaust, flow around the fuselage,
and openings are different so it doesn't need them. I sent you an
email with photos of a plane both with and without the scoops. Hope
that's you're problem. It will be easy to fix if it is. Guys have
spent months and thousands of dollars to find a leak when this was the
problem. In some instances, all it took was 5 minutes to turn the
scoops in the right direction, as they don't work if they're not, in
fact they sometimes make it worse.

Regards,
Bruce Cunningham
N30464

[Dan Thomas]

Andrew Gideon > wrote in message e.com>...
> Our Cessna R182 is getting CO in the cockpit. We've now had three different
> shops look at it multiple times, all to no (complete) effect. They've done
> things like resealing the firewall, the gear-wells, the exhaust, and the
> like. But still we get CO.
>
> We've swapped CO detectors around between planes, so the detectors' results
> are trusted.
>
> One interesting oddity: turning cabin heat on does seem to get rid of the
> CO.
>
> We've noticed no difference made between type of flight. I personally have
> had readings both while XC and while maneuvering (practicing commercial
> maneuvers), and at various altitudes. Others have reported the same.
>
> At this point, we're at something of a loss. The next thing we're trying is
> to extend the exhaust pipe. The presumption is that this would get the CO
> into the slipstream and away.

Extending the exhaust pipe is asking for trouble. There have been a
few exhaust systems failures, and at least one fatal crash, that have
been caused by extending the pipe. The added mass changes the
vibration characteristics of the system, with the extra weight causing
more flex in the pipes near the cylinders as the engine rocks, and
breakage can occur. A busted system inside the cowl is really bad.
Find the entry point. You might note lead stains around the
inside of the entry inside the fuselage. 100LL has lots of lead and
we've found entry points that way.

Dan

[Bob Chilcoat]

That's raises an interesting point. With 100 LL having so much lead, is
there also a problem of chronic lead poisoning over a long time from a small
amount of exhaust getting into the cabin? Obviously it's not an acute
problem, but what about over time?

--
Bob (Chief Pilot, White Knuckle Airways)

I don't have to like Bush and Cheney to love America

"Dan Thomas" > wrote in message
om...

> Find the entry point. You might note lead stains around the
> inside of the entry inside the fuselage. 100LL has lots of lead and
> we've found entry points that way.
>
> Dan

[OtisWinslow]

Check for any cracks at the joint of the pipe and the flange that bolts
to the head. Also at the joint between the muffler and the riser if
you have one.


"Andrew Gideon" > wrote in message
online.com...
> Our Cessna R182 is getting CO in the cockpit. We've now had three
> different
> shops look at it multiple times, all to no (complete) effect. They've
> done
> things like resealing the firewall, the gear-wells, the exhaust, and the
> like. But still we get CO.
>
> We've swapped CO detectors around between planes, so the detectors'
> results
> are trusted.
>
> One interesting oddity: turning cabin heat on does seem to get rid of the
> CO.
>
> We've noticed no difference made between type of flight. I personally
> have
> had readings both while XC and while maneuvering (practicing commercial
> maneuvers), and at various altitudes. Others have reported the same.
>
> At this point, we're at something of a loss. The next thing we're trying
> is
> to extend the exhaust pipe. The presumption is that this would get the CO
> into the slipstream and away. But that "presumption" is really more of a
> "guess" or even a "hope".
>
> Anyone have any suggestions or ideas or experiences that might help us?
>
> Thanks...
>
> Andrew
>

[Andrew Gideon]

OtisWinslow wrote:

> Check for any cracks at the joint of the pipe and the flange that bolts
> to the head. Also at the joint between the muffler and the riser if
> you have one.

*Everything* forward of the firewall has been checked, and much of it
resealed, a couple of times. That's why I'm looking for something "else".

But thanks...

Andrew

P.S. Since we're on the subject, though: "the head" of what?

[Allen]

"Andrew Gideon" > wrote in message
online.com...
> OtisWinslow wrote:
>
> > Check for any cracks at the joint of the pipe and the flange that bolts
> > to the head. Also at the joint between the muffler and the riser if
> > you have one.
>
> *Everything* forward of the firewall has been checked, and much of it
> resealed, a couple of times. That's why I'm looking for something "else".
>
> But thanks...
>
> Andrew
>
> P.S. Since we're on the subject, though: "the head" of what?
>

Cylinder head? doh!

allen

[Dan Thomas]

"Bob Chilcoat" > wrote in message >...
> That's raises an interesting point. With 100 LL having so much lead, is
> there also a problem of chronic lead poisoning over a long time from a small
> amount of exhaust getting into the cabin? Obviously it's not an acute
> problem, but what about over time?
>

Probably some risk involved, but the monoxide is a much more
immediate risk so that long-term exposure to lead isn't an issue:
you'll die in a crash before the lead gets you. I suppose we'll see
leaded fuel disappear from aviation sooner or later anyway.

Dan


> "Dan Thomas" > wrote in message
> om...
>
> > Find the entry point. You might note lead stains around the
> > inside of the entry inside the fuselage. 100LL has lots of lead and
> > we've found entry points that way.
> >
> > Dan

[Ron Natalie]

Andrew Gideon wrote:
> OtisWinslow wrote:
>
>
>>Check for any cracks at the joint of the pipe and the flange that bolts
>>to the head. Also at the joint between the muffler and the riser if
>>you have one.
>
>
> *Everything* forward of the firewall has been checked, and much of it
> resealed, a couple of times. That's why I'm looking for something "else".
>
The only time I get CO in the Navion cockpit is when sitting on the ground
with the canopy open pointed into the wind.

[Andrew Gideon]

I thought I'd let you all know what's going on.

First, a mechanic with whom we checked claimed to be familiar with the
Cardinal's scoops, and said that the R182 had no such thing. Given that
the tail structure of the Cardinal is so different from other Cessnas,
apparently, this isn't too surprising. But I have to admin: I'm still not
completely certain.

However, we've had the extensions installed (although I've yet to see them;
the airplane pulled out as I arrived at the airport yesterday). The
airplane has flown 6.9 tachometer hours since then, and has been showing a
steady zero reading on the CO detector.

So...it looks good at the moment.

- Andrew

[Bruce Cunningham]

Andrew Gideon > wrote in message e.com>...
> I thought I'd let you all know what's going on.
>
> First, a mechanic with whom we checked claimed to be familiar with the
> Cardinal's scoops, and said that the R182 had no such thing. Given that
> the tail structure of the Cardinal is so different from other Cessnas,
> apparently, this isn't too surprising. But I have to admin: I'm still not
> completely certain.
>
> However, we've had the extensions installed (although I've yet to see them;
> the airplane pulled out as I arrived at the airport yesterday). The
> airplane has flown 6.9 tachometer hours since then, and has been showing a
> steady zero reading on the CO detector.
>
> So...it looks good at the moment.
>
> - Andrew

Sounds great! It's always nice to finally solve a problem. How much
did you extend the pipes? I am also interested in how the FAA will
view this. OK or not, as it is a mod to major component. 337 maybe?
Congrats!

Regards,
Bruce

[Robert M. Gary]

Andrew Gideon > wrote in message e.com>...
> Our Cessna R182 is getting CO in the cockpit. We've now had three different
> shops look at it multiple times, all to no (complete) effect. They've done
> things like resealing the firewall, the gear-wells, the exhaust, and the
> like. But still we get CO.
>
> We've swapped CO detectors around between planes, so the detectors' results
> are trusted.
>
> One interesting oddity: turning cabin heat on does seem to get rid of the
> CO.

That's common. Its a well talked about myth that turning off the
heater gets rid of CO. The CO comes around the slip stream and slips
into the cockpit. Also, there really is no way to "turn off" the heat
the doors just aren't that good. I carry a digital CO detector in my
plane. After my last exhaust leak I got 1500ppm with the heat on and
800ppm with the heat off. Still more than enough to make you sad. What
works well is to open lots of windows and blow a lot of air around.
Diluting the air with fresher air keeps the ppm down.

-Robert

[[email protected]]

Robert M. Gary > wrote:
: 800ppm with the heat off. Still more than enough to make you sad. What
: works well is to open lots of windows and blow a lot of air around.
: Diluting the air with fresher air keeps the ppm down.

Sucks for a Cherokee driver that has only one 6x4" window. Lean 'er 'till she
wheezes to keep the CO (and fuel burn, engine deposits, detonation potential, etc)
down I guess. There's no acute effects of NOx are there? :)

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

[Drew Dalgleish]

On Tue, 16 Nov 2004 13:07:57 +0000 (UTC),
wrote:

>Robert M. Gary > wrote:
>: 800ppm with the heat off. Still more than enough to make you sad. What
>: works well is to open lots of windows and blow a lot of air around.
>: Diluting the air with fresher air keeps the ppm down.
>
> Sucks for a Cherokee driver that has only one 6x4" window. Lean 'er 'till she
>wheezes to keep the CO (and fuel burn, engine deposits, detonation potential, etc)
>down I guess. There's no acute effects of NOx are there? :)
>
>-Cory
NO is more deadly than CO. The 8hr exposre limit in ontario is 3ppm
vs. 35ppm for CO

[Mike Noel]

Since noticing this discussion I started looking more closely at the
location of the exhaust stacks on my Archer. They are forward and towards
the pilot's side of the engine air intake. That makes sense since it allows
the prop wash to swirl the exhaust gasses away from it. More interestingly
the exhaust might swirl up past the pilot's vent window, possibly allowing
CO etc to enter the cockpit if that window is not sealed well. This makes
me wonder if some exhaust gasses might enter the Archer's cockpit during
taxi, especially if a scoop is installed in the vent widow.


--
Regards,
Mike

http://mywebpage.netscape.com/amountainaero/fspic1.html
> wrote in message
...
> Robert M. Gary > wrote:
> : 800ppm with the heat off. Still more than enough to make you sad. What
> : works well is to open lots of windows and blow a lot of air around.
> : Diluting the air with fresher air keeps the ppm down.
>
> Sucks for a Cherokee driver that has only one 6x4" window. Lean 'er 'till
she
> wheezes to keep the CO (and fuel burn, engine deposits, detonation
potential, etc)
> down I guess. There's no acute effects of NOx are there? :)
>
> -Cory
>
> --
>
> ************************************************** ***********************
> * Cory Papenfuss *
> * Electrical Engineering candidate Ph.D. graduate student *
> * Virginia Polytechnic Institute and State University *
> ************************************************** ***********************
>