Carbon monoxide in the cockpit of a 180

[Bryan Bowlsbey]

I am getting indications of CO in the cockpit on the cheap, pellet type,"Quantum Eye" CO indicators. Have had the exhaust system tested. They apparently removed the heater cuff, pressurized the exhaust system and looked for leaks, but found only small leaks, which they fixed. They also sealed an opening in the firewall through which the engine monitor cables ran with RTVF. I am still seeing CO indications in the cockpit.

I am looking for ideas to troubleshoot this problem. I am also going to purchase a better CO monitor. Any ideas on where to start looking would be helpful.


OK, update a week later. Have purchased a CO experts model 2010 and it is registering amounts of CO between 0-61 ppm. It peaks when the airplane has some airspeed. Will check and replace the stearing boots as suggested since they are ratty anyway, but will also replace the door seal. With the heater on, and the rear vents open, the level stays below 20ppm in cruise. Hopefully door new door seal and steering boots will help reduce further.

Really apreciate the input. Mechanic closest to where I am stationed was blanked, and I haven't had a chance to get back to our regular mechanic yet due to military duties.

For reference, this seems to be a good article on CO in airplanes:
http://www.aeromedix.com/aeromedix_arti ... index.html

[Michael Rath]

I was getting a little exhaust smell in the cockpit when I first bought my Comanche. I took a close look and the rubber boots that were over the steering arms were cracked. I replaced them and no more smell.

MR

[Kristin Winter]

If the boots are shot, Webco has them. I have also heard that they are identical to the gear shift boot on an early 60's VW bug.

[David Pyle]

Beetle?

[Zach Grant L1011jock]

They are CV joint boots... You have bad door seals, and are probably not running with any air coming into the cabin. If you open a vent or pull the heat on, does the the CO go away? What happens is, with bad door seals, the relative low pressure of the slipstream sucks the air out around the door, which in turns sucks air up through the belly, bringing exhaust with it. Openeing enough freshair vents to eaual the volume of air being lost out the door seal will fix the problem, and conversely fixing the seals, will reduce the amount of air needed to keep the bad stuff out.
-Zach

[Tom Deml]

Zach, I own a 1960 250, serial #2030, i,ve been battling CO levels of 10 to 25 ppm during these colder weather months (I'm in MN). I think this has been going on for years. I discovered if I block the belly vent, parked and running, I get no CO. However when I start to taxi I start to get up to about 15ppm. Still problems with the vent blocked even during climb and cruise. with the belly vent unblocked, i get CO parked, taxi, climb, and cruise. with heat and/or defrost on, levels drop. i can clear the detector to zero with full defrost and have the detector sit on the glare schield(so I believe I don't have a cracked muffler), but still get readings of 10-15ppm on floor. I can clear detector with a side vent open but will then succumb to frostbite. With heat/defrost off levels climb in cabin to 25ppm range. Seems like a noticeable amount of "negative" pressure in the back seat area drafting in cold air. CO levels are always higher in back seat area. You believe this is a door seal problem? Besides the door seal, any other possible culprits?
Tom Deml

[Zach Grant L1011jock]

The simple fact is that the relative low pressure of the slipstream going around the fuselage is going to suck the relatively high pressure air in the cabin out of any hole that it can. The air on top of the wings and the air going around the more curved upper areas of the fuselage are going to have lower pressure than that of the air under the fuselage going relatively straight ( thank you Bernouli). If you add it all up, the air is getting sucked out of the cabin through bad seals, or other holes, and needs to be replaced with other air. You can either ram more fresh air in through vents causing the cabin to be slightly higher pressure than the air containing exhaust under the belly, or you need to seal all of the holes that might let air out on top. What you have said is very indicative of the bad door seal situation I describe. In my 180, I have pretty good door seals, but by far not perfect, as well as the cherokee door latch, but I still run with the cabin air on all the time. If it is too cold to have the cabin air on (not the side vents, just the underpanel air vent) then the cabin heat is on full blast and there is plenty of air to keep the fumes down below. You will never get the airplane to be airtight as there needs to be drain holes in the belly and the doors still need to open, and are subject to pretty high air loads. You can close down most of the under wing gaps in the fuselage with some HVAC type aluminum tape around the landing gear conduit openings etc. You can get it sealed good enough to be able to control the situation. It just takes the analysis of where the air goes, and time to mitigate the deficiencies.
-Zach

[Tom Deml]

Thanks Zach. I'll likely redo the door seal and double check the usual suspects under the back seat. I can see that the mechanicals for the gear are well sealed coming into the gear wells. will check the spar itself and cabling openings. You know I've never tried using the under the panel vents to clear and keep it CO free. That air will be warmer than the side vents for "make up air". Somehow I've got to find some improvement so that belly vent starts to become an exit for air rather than an intake. These old birds sure need their share of loving.
Tom

[Tom Deml]

Zach, one other question....are you familiar with the Avtek door seal solutions? When I replaced the door seal several years back I used a Webco suggested 1/4 round type product. It took hours to try to customize it to fit. It's obviously not working well. The Avtek 02/02 product looks like it should work well. Your thoughts?