CO leak thoughts?

[dkkim73]

Hi All, 

I fly with a Forensics-branded CO meter stuck on the panel and had been until recently seeing 0 through all phases of flight, except taxi with door or window open (seemed predictable). 

A few weeks ago I noticed levels in teens-40's, seemed more on climb, cleared with aggressive use of the vents. 

Recently, saw up to 90ppm(!) during climb. Local shop did a leak check by pressurizing the exhaust and spraying it with LeakTech (SP?), said no leaks. Mechanic suggested I may have been using partial cabin heat (should be all or nothing)... this did not seem to be the problem. Moving the detector around in flight did not show any obvious gradient. Also, the opening for cabin vent and heat showed "0" with the detector. 

I can clear it back to 0 in cruise.  Occasionally see some lower levels (20s) on descent. It "feels" to me to vary with angle of attack  based on these observations.  

Asking around, including a senior mechanic at Savvy known to many, pointed me at the following: 

- landing gear actuation rod "mouse boots"; it turned out one was loose at the outboard end, re-taped. Next flight showed lower (40-50ppm) but still high levels

- no obvious leak from door but I need to troubleshoot that more completely in flight

This did not happen right after the cylinder work, but over 10 hours later. I cannot recall a specific maintenance item recently that would affect the floor or belly area. 

Thinking maybe landing gear doors might be slightly out of rig? (pressurizing the wheel wells at higher AOA)

I realize there's no magic bullet, here, but wanted to post in case one of the Hive Mind had some additional specific insights. 
 

Thanks for any thoughts!
David

 

[Ragsf15e]

42 minutes ago, dkkim73 said:

Hi All, 

I fly with a Forensics-branded CO meter stuck on the panel and had been until recently seeing 0 through all phases of flight, except taxi with door or window open (seemed predictable). 

A few weeks ago I noticed levels in teens-40's, seemed more on climb, cleared with aggressive use of the vents. 

Recently, saw up to 90ppm(!) during climb. Local shop did a leak check by pressurizing the exhaust and spraying it with LeakTech (SP?), said no leaks. Mechanic suggested I may have been using partial cabin heat (should be all or nothing)... this did not seem to be the problem. Moving the detector around in flight did not show any obvious gradient. Also, the opening for cabin vent and heat showed "0" with the detector. 

I can clear it back to 0 in cruise.  Occasionally see some lower levels (20s) on descent. It "feels" to me to vary with angle of attack  based on these observations.  

Asking around, including a senior mechanic at Savvy known to many, pointed me at the following: 

- landing gear actuation rod "mouse boots"; it turned out one was loose at the outboard end, re-taped. Next flight showed lower (40-50ppm) but still high levels

- no obvious leak from door but I need to troubleshoot that more completely in flight

This did not happen right after the cylinder work, but over 10 hours later. I cannot recall a specific maintenance item recently that would affect the floor or belly area. 

Thinking maybe landing gear doors might be slightly out of rig? (pressurizing the wheel wells at higher AOA)

I realize there's no magic bullet, here, but wanted to post in case one of the Hive Mind had some additional specific insights. 
 

Thanks for any thoughts!
David

 

Obviously, first thing to rule out is the heater leak but it sounds like you’re doing that.

If it goes back to zero in cruise without much effort, it seems most likely related to aoa/swirling/cockpit leak through the rat socks, floor, or door(s) which might only affect climb.  Another leak point is the wire bundle going out the back of the luggage into the avionics bay.  Mine actually pulls air in from there.

What does it do on the ground?  It might not be zero, but should be pretty close unless you have a tailwind or crosswind blowing exhaust up around your leak.  If you’re seeing a leak on the ground as well, I might look closer at the heater and even firewall.  If it’s say below 20 on the ground, high in climb, and zero in cruise, I’d focus on finding the leak.  Unfortunately, our cockpits leak, so you’re looking for the leak that’s letting in CO, not all the other ones.  Probably start with the two door seals and the floor?

At least on mine, the door seems to let air out, not in, so that seems less likely, but that air is coming in from somewhere…

[exM20K]

How good is your door seal? I have to put a piece of paper in the bottom corner, where it sticks nicely and reduces sound levels dramatically. That sort of leak will create a low pressure situation in the cabin and really suck in the CO.

It is not uncommon to see 20's in the climb for me. It clears quickly, so I consider it NBD.  Ditto on taxi back to the hangar.

-dan

[EricJ]

Non-pressurized airplanes generally leak like crazy.   If you ever pull your carpet up you'll see there are huge gaps and holes all over the floor, built that way from the factory.    The belly isn't sealed, either, so air can flow through the belly and floor pretty easily when it wants to.   Positive angles of attack tend to be worse in most airplanes, I think for the reason that the belly/floor is so leaky, and it can just get through more easily.    At cruise it just slips by more easily and the vents bring in more than can leak in, so for many/most airplanes it seems like CO goes to 0 or close to it in cruise.

Mine used to be worse than it is, and the main thing I did was just cover up some of the holes under the carpet with foil tape.   It got a lot better, essentially good enough that I don't worry about it any more since it's 0 at cruise and not very high the rest of the time.

We used a leaf blower and some soapless bubbles on a friend's (non-Mooney) airplane to find and fix a ton of leaks.   It still leaks, just tolerably now. 
 

[N201MKTurbo]

The fuselage generally has low pressure on the outside. So it sucks air out of it. Most of the ventilation air comes from the upper cowl or purpose built scoops to raise the air pressure. 
 

Things like low hanging gear doors and such can form air scoops that pressurize the wheel wells and also pressurize the belly if your rat socks aren’t perfect. The wheel wells are near the exhaust stream. 

[PT20J]

However it is getting in, remember that CO in the exhaust is high at rich mixtures and very low when LOP.

[Fly Boomer]

3 hours ago, EricJ said:

We used a leaf blower and some soapless bubbles on a friend's (non-Mooney) airplane to find and fix a ton of leaks.

Did you use a home brew bubble media, or is there a commercial product you like?

[EricJ]

1 hour ago, Fly Boomer said:

Did you use a home brew bubble media, or is there a commercial product you like?

There's a recipe in the M20J SMM, but Spruce used to sell a mix that (iirc) is what we used.    I can't find it on Spruce any more,  you could still mix up the stuff in the SMM.   Very mild soap could potentially be used and then rinse the crap out of everything when you're done, too, if you're careful where it goes.

Edit:  Spruce still sells this stuff, which looks like it'd be reasonably suitable (pH = 6.9-7.5).

https://www.aircraftspruce.com/catalog/appages/detectorfluid08-12291.php

 

[N201MKTurbo]

I’ve found the best leak detection fluid is kids bubble solution for blowing bubbles. You can get a lifetime supply in the toy department at Walmart for less than $5

[1980Mooney]

8 hours ago, dkkim73 said:

Hi All, 

I fly with a Forensics-branded CO meter stuck on the panel and had been until recently seeing 0 through all phases of flight, except taxi with door or window open (seemed predictable). 

A few weeks ago I noticed levels in teens-40's, seemed more on climb, cleared with aggressive use of the vents. 

Recently, saw up to 90ppm(!) during climb. Local shop did a leak check by pressurizing the exhaust and spraying it with LeakTech (SP?), said no leaks. Mechanic suggested I may have been using partial cabin heat (should be all or nothing)... this did not seem to be the problem. Moving the detector around in flight did not show any obvious gradient. Also, the opening for cabin vent and heat showed "0" with the detector. 

I can clear it back to 0 in cruise.  Occasionally see some lower levels (20s) on descent. It "feels" to me to vary with angle of attack  based on these observations.  

Asking around, including a senior mechanic at Savvy known to many, pointed me at the following: 

- landing gear actuation rod "mouse boots"; it turned out one was loose at the outboard end, re-taped. Next flight showed lower (40-50ppm) but still high levels

- no obvious leak from door but I need to troubleshoot that more completely in flight

This did not happen right after the cylinder work, but over 10 hours later. I cannot recall a specific maintenance item recently that would affect the floor or belly area. 

Thinking maybe landing gear doors might be slightly out of rig? (pressurizing the wheel wells at higher AOA)

I realize there's no magic bullet, here, but wanted to post in case one of the Hive Mind had some additional specific insights. 
 

Thanks for any thoughts!
David

 

Did you check the boots around the rudder/brake linkage boots?  The leakage could be coming from right around your feet.  Even in good condition those cannot seal very well because there are two rods with the brake rod moving up and down as the entire linkage moves fore and aft. (see the first 2 pictures.)  The last 2 pictures are an Ovation boot salvage at Dawson.  You can see the hole in the boot where the linkages protrude forward.  

  

 

 

[larryb]

I see different numbers in climb vs cruise vs descent. If the cowl flap is fully open on landing the alarm will sound.

Generally I see 20 in climb and 0 to 5 in cruse. This is over two mooneys.

I did have elevated numbers for a bit and found a missing camlock on the front of the belly pan that was causing it.

[Z W]

I would start by pulling the carpet and any padding under it, and then applying high-quality duct tape over all the holes and gaps in the floor, if someone hasn't already done that.  There are a lot of holes and gaps.  This has a bonus benefit of keeping loose/dropped hardware, dirt, and gunk from falling down inside your floorboards too.

If that doesn't fix it, you can move on to checking the cabin penetrations one by one.

[Fly Boomer]

9 hours ago, EricJ said:

Edit:  Spruce still sells this stuff, which looks like it'd be reasonably suitable (pH = 6.9-7.5).

I saw that.  Looks like its primary purpose is to not ignite in the presence of oxygen, but seems like it’s pretty inert in general.

[Fly Boomer]

8 hours ago, larryb said:

I did have elevated numbers for a bit and found a missing camlock on the front of the belly pan that was causing it.

That’s a bit alarming.  I would not have guessed that such an insignificant opening would show up on the detector — it’s not like the belly is a super-tight seal even with all the camlocs in place.  What kind of detector do you use?

[exM20K]

@dkkim73 also note how the left side exhaust dumps under the fuselage whereas the right goes a bit outboard.  The acclaim is burning 33-36 GPH in the climb, so that engine is making a lot more CO than 200or 210 HP engine.  I don’t recall the full power/full rich fuel flow on my 231, but 150% of the 231’s horsepower is probably producing 150% of the CO.

-dan

[larryb]

That’s a bit alarming.  I would not have guessed that such an insignificant opening would show up on the detector — it’s not like the belly is a super-tight seal even with all the camlocs in place.  What kind of detector do you use?

I use the sensorcon. It wasn't a huge amount more CO or even enough to trigger the alarm. But it wasn't enough to make me look around. I don't recall exact numbers.

[PeteMc]

Following up on what @Eric J said....  After my interior was done I noticed these giant holes in the floor by the center console.  Talked to my mechanic and he said they were just covered up by the old carpet that had probably just been installed closer to the center and covered them.  

So do check for openings and maybe worn/thin carpet where fumes are coming through from the engine compartment. 

 

[PT20J]

If the exhaust system doesn’t have leaks, the only source of CO is the tailpipe. Therefore, any entry point would have to be aft of the tailpipe.

[PeterRus]

How old is the CO sensor? They have ~2 year lifespan. 

Edited November 18, 2024 by PeterRus