ijs12fly Posted May 12, 2019 Report Share Posted May 12, 2019 I am chasing a CO issue - two shops have yet to find a leak. Yesterday while sitting at idle getting ready to shut down, I closed my "Vent cable" on the Center Console and noticed I still had some air coming thru the vent. I have never really checked if OFF is 100% "off" before. The Heat cable was fully closed as well. I looked under the passenger side and the cable is working fine - the slider in the vent box opens and closes smoothly, and appears to be fully closed with the cable pushed in. So my question to other M20C owners - when you get a chance - could you see if you still get some air flow thru the Center Console Vent with the VENT cable fully closed. (and heat off). Need to have engine running for this test, or test in flight. Thanks Quote Link to comment Share on other sites More sharing options...
Rwsavory Posted May 12, 2019 Report Share Posted May 12, 2019 I know for a fact that there is no airflow through our center event when in the closed position. You might want to check the floor to see if there are some openings. Some aluminum tape will fix that up. Quote Link to comment Share on other sites More sharing options...
smwash02 Posted May 12, 2019 Report Share Posted May 12, 2019 Adding to @Rwsavory's notes. Pull the carpet, seats, and side panels, there's many holes there. The spar area is also not sealed unless there's tape there. There are other passageways at the rudder pedals and center console area where the flap actuator and pushrods are. Have you smoked your exhaust? Pinholes in the exhaust will get CO2 into the shroud piped into your cockpit. When the cabin air is off I don't get any air in the cabin from there, but there's plenty of drafty spots that remain -- windows and wemac vents, though those should help your CO2 problem not hurt it usually. Another path you can take is pulling the SCAT hose off of the inlet on the FWF side from the exhaust shroud. Just pull the cheek and cover up the inlet. Make sure your tests are into the wind with the door closed. Quote Link to comment Share on other sites More sharing options...
Jim Peace Posted May 12, 2019 Report Share Posted May 12, 2019 5 hours ago, ijs12fly said: I am chasing a CO issue - two shops have yet to find a leak. If your CO detector is portable and shows parts per million, I wonder if you could just position it to all the areas in the cabin to see where it registers the most....I had some holes behind the rudder pedals that are now sealed.... I did have an issue recently that turned out to be scat tubing that detached in the cowling and I was getting engine compartment air in the cabin..... CO detectors should be mandatory...... Quote Link to comment Share on other sites More sharing options...
ijs12fly Posted May 12, 2019 Author Report Share Posted May 12, 2019 (edited) Thanks gents for the timely replies - So I do have a 2 different CO detectors - a Quest Technology one (10-15 years old) and new Sensorcon I picked up a few mo's ago. I will try that idea about moving it around to find the "hot spots". For now its attached to the passenger front seat pocket - so its reading what ever comes out of the Center console vent. I have some more testing to do but what I have noticed so far is with Heat Off, on Takeoff and Climbout, i get about 25--30 ppm, and then once I level off it drops to zero. If the Heat is on, the reading is closer to 80ppm during takeoff and climb, then it drops to <6ppm or so once I level off. I will set up a test plan on go out and test each case in a more scientific manor. I recall in the past that when my vent was off I would not get any flow in from that vent, but started to doubt that based on current observation, and I wasn't 100% sure. So this potential leak in the fresh air Vent is suspect as a contributor given the exhaust is on that same side of the plane and may be coming in during takeoff and climb. Hoping to hear from a few more C owners if their Vents are also 100% "off" when the control is closed. Edited May 13, 2019 by ijs12fly Quote Link to comment Share on other sites More sharing options...
Ragsf15e Posted May 13, 2019 Report Share Posted May 13, 2019 So not a C, but flew my F today. Off isn’t 100% off. Sensorcon shows about 25 ppm during ground ops depending on wind direction. Maybe 10-15 in climb. Quickly to zero in cruise. 80 would definitely concern me. 1 Quote Link to comment Share on other sites More sharing options...
carusoam Posted May 13, 2019 Report Share Posted May 13, 2019 I always invite @DanM20C for CO discussions... IJS, Expect the older the CO sensor is the more unusable its data is... Sensorcons can be re-calibrated. But, the 10+ year old one may not be working very predictably... When the sensor is getting a reading... it can be moved to every air stream to best determine where it is coming from... To be serious... upon the next start-up... open the heat supply... put the sensorcon in the air stream to see what it says... To be realistic... if the sensorcon is giving a high reading in the climb, but zero in cruise without changing the heater setting... it probably isn’t the heater... Elevated CO levels need to be taken care of... But, if it is being delivered by the heat system... this is a take care of it now situation... the heater can accidentally deliver more CO than a human can handle... old heat muffs have developed interesting ways to fail... So if you pull the hot air knob, feel hot air coming out, put sensorcon anywhere near the stream... see what it is saying... The reason for the aggressive take action now explanation.... the failed heater muffs have a tendency to have their crack initiate on one day... and tear wide open (propagate) on a couple of flights later... Expect that when you remove the cowl... any exhaust leaks can be the problem... they have a tendency to leave marks in surprisingly obvious manners... Briefly, if you are seeing a 30 on your sensorcon....nobody else does... this is not normal... Seeing 80 is not an accidently high number... that is something to be concerned with... CO delivered through the cabin heat can be dangerous... CO entering the cabin can be a sign of an exhaust leak... exhaust leaks near the exhaust valve can also be leaking flames... another reason to be looking to identify the source of the high reading... PP thoughts only, I would want to know what is causing the high CO readings before flying it again... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
carusoam Posted May 13, 2019 Report Share Posted May 13, 2019 as far as how your heater control valves work... you would have to say what year your plane was built... And how well the slide gates were maintained... this year... My 65C slide gates had a tendency to acquire rust over a year and stop working just before annual... Winter annual was a good time to get them working again... Rusted slide gates don’t cause CO... they just allow it to enter the cabin better... Note on CO poisoning... CO doesn’t exit the blood stream very quickly... so your CO levels in the blood have a tendency to rise continuously with small amounts available in the air you breathe... Fingertip O2 sensors will give erroneous readings, as their sensor is confused and thinks CO looks like O2... giving good looking readings even though they are false... PP thoughts trying to help an MSer out, not a CO expert... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
kpaul Posted May 13, 2019 Report Share Posted May 13, 2019 8 hours ago, Ragsf15e said: So not a C, but flew my F today. Off isn’t 100% off. Sensorcon shows about 25 ppm during ground ops depending on wind direction. Maybe 10-15 in climb. Quickly to zero in cruise. 80 would definitely concern me. Even your numbers are high compared to my F, also using a Sensorcon. On the ground, it depends on the wind direction and if the door is open, however it is generally 10 or less with the door open. In the climb I sometimes see 1-2 but most often it reads 0. It has always been 0 in cruise and descent. Quote Link to comment Share on other sites More sharing options...
Ragsf15e Posted May 13, 2019 Report Share Posted May 13, 2019 3 hours ago, kpaul said: Even your numbers are high compared to my F, also using a Sensorcon. On the ground, it depends on the wind direction and if the door is open, however it is generally 10 or less with the door open. In the climb I sometimes see 1-2 but most often it reads 0. It has always been 0 in cruise and descent. Yep, it’s not concerning high, but I’d like lower numbers. Sealing it up better is on the list next time the carpet and seats are out. The list on 50+ year old airplanes never seems to get shorter, only longer. 1 Quote Link to comment Share on other sites More sharing options...
0TreeLemur Posted May 13, 2019 Report Share Posted May 13, 2019 On 5/12/2019 at 8:54 AM, ijs12fly said: my question to other M20C owners - when you get a chance - could you see if you still get some air flow thru the Center Console Vent with the VENT cable fully closed. (and heat off). Need to have engine running for this test, or test in flight. When the vent and heat knobs are full forward, there is NO air flow through the center console vent in our '67 C. Good luck. Quote Link to comment Share on other sites More sharing options...
ijs12fly Posted May 14, 2019 Author Report Share Posted May 14, 2019 On 5/13/2019 at 12:16 AM, carusoam said: as far as how your heater control valves work... you would have to say what year your plane was built... And how well the slide gates were maintained... this year... I see you added Dan B, i purchased my Sensorcon after camping next to him at OSH last year. My aircraft is a 1977. Last of the C's. Based on all the great feedback - I can assume I do (at a minimum) have a leak on the Cold side. What can I check on the Fresh Air Slide Gate? The casing looks immaculate, no corrosion, the motion seems normal, no sticking, fully swings with the cable movement. This is is looking at it with out taking anything apart. Is it serviceable? I don't recall ever seeing anything written up on an annual stating they gates were ever serviced. Can I simply take it apart and inspect? Is there some type of seal that needs to be replaced? I will do some more testing this weekend and capture what the CO is in different configs, with Heat On/Off, Vent On/Off, taxi, climb, level cruse to see if I can narrow down the cause. Thanks for all the input. Steve Quote Link to comment Share on other sites More sharing options...
carusoam Posted May 14, 2019 Report Share Posted May 14, 2019 Steve, Dan does a great job of explaining the challenges of CO from an interesting first hand experience... How Familiar with the removing the cowl and taking a look are you? The slide gates are pretty easy to put your eyes on... I used to do it at annual... so it may take disassembling some hose to get a real good look at it... My 65C version of it, the slide gates carried enough surface rust to impede their motion... if your gates have full motion, they probably aren’t an issue... Non moving slide gates won’t cause a CO problem... it just allows the problem to go further get into the cockpit... With the elevated CO level you are seeing.. you may want to take a look to see if there are any signs of exhaust leaking out around the exhaust pipes... Look for leaking pipes... When able, or when it makes sense there are ways to look up inside the exhaust system with a dental camera... If your Sensorcon indicates the CO is coming out through the heating system... have your mechanic help you take it apart for a good inspections... Take pics, post what you find... The inside of the muffler is a horrible environment. Even specialty metals don’t stand up very well over the years... PP thoughts only, not a mechanic... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
Hank Posted May 15, 2019 Report Share Posted May 15, 2019 Exhaust leaks have telltale gray color around them, easy to spot under the cowl. 1 Quote Link to comment Share on other sites More sharing options...
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