Cabin Heat and C02

[n8340a]

I just had a new exahaust system installed on my 52 170b. Engine is C-145. On the way home, high CO2 levels were indicated when the cabin heater was pulled open. Took the airplane back to the mechanic and we are stumped. New muffler was pressure tested and all the slip seals and other safeguards indicate its not a leak. Any suggestions or help? One idea is that the stacks dont stick out far enough from under the cowl (about an inch now) and its slipping back up in the cowl somehow and building up at excessive levels.

Thanks
Bill

[Robert Eilers]

Sounds like your exhaust stacks are similar to mine. I notice exhaust smells on the ground if the cabin heat is opened. As a result, I close the cabin heat when on the ground cleaning up after landing and don't open cabin heat until at cruise climb speeds after takeoff. When the cabin heat is opened in flight I do not notice the exhaust smell and so far have not registered CO-2 on my detector.

[Bruce Fenstermacher]

Bill you may have found the problem but stock exhaust don't stick out much more than an inch or so from the cowl.

I'd look around for some extenstions that just slipped over what you have to at least test and see if that is the solution. Then if it is have you exhaust extended. My exhaust stick about 3 inches below the cowl.

[blueldr]

Are you guys talking about CO2--Carbon dioxide, the gas causing warming of the Earth, or are you concerned about CO--Carbon Monoxide, the potentially deadly gas?

If it really is CO2 that is your problem, stop washing down the engine with Coca Cola.

[n3833v]

I tried extensions and didn't help. My exhaust is just outside cowl. I only get co2 when climbing out until cruise. I assume the pilots door seal is my possible culprit and need to replace the seal. I don't get too high a reading when climbing, but it still bothers me.

John

[4583C]

Are you guys talking about CO2--Carbon dioxide, the gas causing warming of the Earth, or are you concerned about CO--Carbon Monoxide, the potentially deadly gas?

If it really is CO2 that is your problem, stop washing down the engine with Coca Cola.

Chalk up another for the geezer!

[Jr.CubBuilder]

I had the same problem even though I had exhaust extensions that came out of the lower cowl at least six inches. It turned out to be a number of different problems. Check your risers where they connect to the cylinder, I had a couple of those leaking bad. Also while it looked ok at first glance I eventually found about half a dozen unsealed holes in the firewall, so you might give that a look. I've heard the opening for the left side landing gear can be another source on climb out as the air swirls around that way. For me the holes in the firewall, and the leaks in the riser to cylinder seemed to be the culprit. There's a lot of area behind the motor for stagnant air to swirl around, any exhaust leaks just seem to find there way there and on climb out and for whatever reason the cabin pressure seems to be a bit less than under the cowl during climb out. I also have a little air vent/scoop on the rear window that I now open to help pressurize the cabin during long climbs even in the winter.

[Robert Eilers]

Good point about the left side landing gear fairing. I placed a gasket under mine - made a difference.

[GAHorn]

There should be a rubber gasket at the gear legs.

It's unlikely that leaks at the riser-to-muffler clamps are the source of CO in the cabin. If/when exhaust leaks there, it is instantaneously at atmospheric pressure. Even tho' it is just above the cabin heater shroud (which surrounds the muffler), it's unlikely any of that exhaust gets into the system, because the interior of the heater muff should be at higher than atmospheric pressure due to ram-effect from the inlet at the nose-cowl. Therefore, exhaust (at lower pressure) cannot enter the heater-shroud which is at higher-than-atmospheric pressure.

Some oft-overlooked sources of the cabin getting exhaust gases are:
Mufflers that "look" OK, but are not actually pressure tested with soap.
Poorly fitted or worn heater mixing valve, in conjunction with above.
Poorly fitting doors and door seals.
A lower rotating beacon mount and/or poorly sealed belly antenna mounts.
Leaking baggage doors/seals on aircraft with baggage doors on the left side (where a clockwise prop-wash brings the exhaust flow.)
Leaky firewalls, especially at the lower edge with the fuselage. Also be aware of rivnuts or nutplates which were intended to secure the rudder-pedal floor-plates to the firewall. If no screws are installed in those rivnuts/nutplates then quite a few of them may be leaking into the cabin.
A tail-cone (which is fairly open back at the very back) which allows exhaust to flow forward into the cabin. (I installed a rear bulkhead above/behind my hat shelf which stopped it for me. The airplane ordinarily had only the headliner between the shelf and the tailcone. Installing a sheet metal bulkhead and insulating it with foam-backed foil also got rid of noises from the tailcone while taxying. That tailcone was like a megaphone bringing tailwheel-over-the-tar-strips and rough runway noises oil-canning into the back seats, as well as slapping cables, etc etc. I had no idea what rear seat pax in a 170 heard until I was back there in someone else's without a headset.

Dr. West addressed CO poisoning at the Galveston Convention seminar and he strongly urged all owners to obtain a CO monitor, even a non-aviation type, if necessary. ANY type monitor is better than none (and better than that little cardboard colored "dot" for the dashboard. Dont waste your money on those.)

[Jr.CubBuilder]

(and better than that little cardboard colored "dot" for the dashboard. Dont waste your money on those.)

Whoa there George, I have to take exception to that statement! One of those little "dot" gizmos saved my life, and they're cheap!

Interestingly enough I had a fairly expensive battery powered CO detector that didn't alarm I think because of how the cabin air was circulating. The cheap dot that had turned almost black clued me in to reality right about the time I was starting to drool on myself.

Get more than one indicator, batteries die, chemical types like the dots are subject to age and humidity.

[GAHorn]

Good points. The problem with those little "dots" are:... they are usually out-of-date and ineffective, ... and they are horribly IN-sensitive. You are luck, and I am happy it worked for you! Tell us more!

[Jr.CubBuilder]

I can tell you from personal experience that the initial effect of CO poisoning for me was a sense of euphoria that continued to build as time went by, the closest comparison I can make would be like the first couple puffs of nitrous at the dentists office. Later I began to feel that something wasn't quite right, just a nagging sense that I was forgetting something. I began scanning the panel looking for something wrong but everything seemed right yet I still had that vague nagging feeling, eventually I noticed the dot on my little CO detector had turned black. I thought "why does that thing look so dark with my shades on" and slide my sunglasses down my nose to look at it. Everything went fuzzy at that point but the dot still looked really dark so I started leaning forward and looked at it a couple more times sliding my sunglasses up and down my nose. The color didn't change but it kept getting fuzzy when I slid my sunglasses down. I realized at some point that I hadn't put my contacts in that morning and I was wearing my glasses instead of my sunglasses. I sat back sort of sloppy like band now I could tell I was slumping in the seat and as my brain digested the information like a drunk slogging through mud, I got a huge adrenaline rush. My legs started shaking, my heart started pounding at a ridiculous rate. I turned off the heater, opened the vents and a window.

This whole situation took a fair amount of time to develop it didn't just happen in the space of a couple minutes. I was flying out of a strip that had a long extended climb to clear a mountain, about 30 minutes of steady climbing. The saving grace for me was that shortly before I was really in trouble I had cleared the last ridge and set up for another hour plus of cruising to the next fuel stop, everything was trimmed out and I was just chugging along.

Once I had come to terms with my situation I wanted in the worst way to just land at an airport I could see of my left, but the next stage of CO poisoning had set in and I discovered I couldn't remember the frequencies for the field, nor could I even find it in the AFD. I could look at the old steam gauges but they didn't make any sense, so I just sat there with my right hand hanging out in the breeze while my knees continued to shake and battled with everything I had not to nod off.

I was flying with some new friends I had just met and we were all on the same frequency, I could hear them but was to addled to talk, so I just sat there grinding along with the window open and something flapping around behind me. When we eventually got near our breakfast stop I had enough wits about me that I could land although I almost used a taxiway till I noticed another plane on downwind for the right runway. We were down on the ground for probably about two hours getting an airport car, waiting for food, refueling etc. I felt sick, hungover, and my skin seemed flush and hot, but I was getting better. I flew the rest of the way home with the vents wide open and no heat.

I had a battery powered CO detector in the plane as well that never went off, I have since come to the conclusion that it's location clipped to the side panel right next to the door must have left it in a pool of clean air circulation. I tested both the battery powered unit and my little CO detector card later. It was interesting that the card (which was still less than 90 days since opening) would not change color when held against the exhaust of my truck for two minutes, however 45 seconds in the exhaust of a four stroke motorcycle with the choke on turned it black. The battery powered unit actually alarmed after only about 30 seconds in the bike exhaust and about two minutes behind the truck.

So here's my couple of thoughts, the battery powered unit is good as long as the battery is good and it would be best to attach it somewhere near your head so it's sampling the same air, the shoulder harness seems like the spot. The little CO cards I buy a dozen at a time, date them when opened, and I now place them on the panel where they really can't be missed right in front of my face next to the HSI, before I had it partially hidden under the copilots yoke.

CO binds to your hemoglobin tighter than oxygen, the result is basically the same as hypoxia, the only salvation is time and clean air. I'm continually surprised at how many of my fellow pilots don't know this. If you haven't read up on it you should, it could save your bacon.

[doug8082a]

Thanks for sharing your story and being candid about what happened. It's a great lesson and very interesting to hear how the diferent CO detectors reacted to both CO exposure and location within the cockpit.

[n8340a]

Wow, I'm a new 170 owner (traded up from a 120) an this is my first post to the forums. I am blown away by the response, thanks everyone (even you blueldr!). This is great info in that I'm ussually flying with my family, if it was just my butt thats one thing... Have not tried any of these fixes yet but will soon and will let you know....
Thanks!
Bill

[n3437d]

I happen to be one of those using the "little dot" It has not changed color and they are "good" for 90 days after opening the sealed wrapper. I cannot comment one way or another on the accuracy as I have never had a case of excessive CO at least no symptoms. One of the very first tasks my former A/I did (and he is also a 170 owner) was to seal every and I do mean every opening or hole on the firewall. I am fortunate in that my plane is extremely wll sealed. Being a glider pilot as well I know how important it is to seal a glider which translates to sealing a powered plane as well. Oviously there are more limitations as to what can be sealed on a power plane without endangering control surfaces but I did use calk and stretch tape to seal around legs where they meet fuselage and wing roots and other open areas. My plane is hangared and therefore I do not run the risk of trapping moisture (also live in a very low humidity state).

But.... I have seriously been looking at the new self contained and hard wired CO detectors - money worth spending.

Joel
N3437D