CO mystery - any ideas?

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 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.

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

"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/

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

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

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

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

Andrew Gideon wrote in message gonline.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

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.