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