No Cabin Heat with Cowl Flap open

[N811SS]

Hello All -

Quick question -->  My 1967 M20F will only provide cabin heat when the cowl flap is closed.  Problem is that on cold days (and nights) I still need to leave the cowl flap open (or at least trailing) to keep the the CHTs below 400 degs.  I find myself switching between cowl flap closed so I can get some heat in the cabin to defrost the passengers or half-open to get the CHTs cooled off with the air vent closed to prevent the cold air from rushing in.  I checked the SCAT tubes and don’t see any holes/ripes and I checked the movement of the lever in the heater box and it seems okay.  With the cowl flap closed it cranks out the cabin heat just fine.  Maybe that is just the way these old Mooney's are but it seems like a crazy design...I do have the 201 cowling mod installed on N811SS and there have been all manner of mods/changes done to this machine over the years.

 Does anyone else have the same issue?

[spaz]

I have noticed that in my 88 J. I attribute to the exhaust manifold getting much more cold air

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[N811SS]

I thought of that possibility as well.  For example, with the cowl flaps closed there is more air pressure under the hood and therefore more airflow through the scat tube air intake next to the air filter.  However, i have not really experienced a larger "volume" of air (i.e blowing stronger) coming into the cabin when the cowl flap is closed only that it is much warmer.  This weekend I will take the lower cowling off and snaps some photos.  Maybe the scat tube plumbing is in some way in correct.  thanks for the reply.

[KSMooniac]

Same behavior in my J.

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[Yetti]

sounds like a problem with the "intake" scat tubing.   on the F that would be the left side down lower....

[tony]

I'm kinda thinking you need to fix the CHT problem before anything else.  Is your baffling good?

[carusoam]

Things that effect good heating...

1) Heat source: High EGTs are good.   LOP is bad for cabin heat.  Deep LOP, is terrible... 100° ROP is pretty good, peak is better...

2) Muff around the exhaust.  Heat is transferred from the exhaust using this device.  See if it is assembled properly.  It gets undone at annual...

3) Air box.  The place where two tubes deliver hot air from the muff and cold air from outside.  Check the cables and knob operations....

4) Altitude. Altitude is a good source of low EGTs...

5) cowl flaps...  only if they are affecting something above on this list...

6) Chilly OATs...  leaking airbox equipment can bleed cold air through the system...

7) Leaking vents and door seals in the cabin don't help very much...

PP ideas, not a mechanic...

Best regards,

-a-

[jetdriven]

20 hours ago, KSMooniac said:

Same behavior in my J.

Sent from my VS985 4G using Tapatalk
 

 Same here. With Cowl flaps open so much air gets pullee past the exhaust, I think it is cools it off so much that it can't provide any useful heat. 

[Bob_Belville]

The PFS exhaust is supposed to be poor for cabin heat. Someone who ordered one recently for his J tells me they now offer an add-on heat exchanger for buyers north of the MD line. 

My recollection of the M20E I had 30 years ago was that the heater would drive you out. Don't know what the difference was.

[Ron McBride]

You temps are way to high.  My heater will burn you out of the plane.  I also can takeoff in the winter with cowl flaps closed when temps are in the 50's and cooler.  I have a Lasarmod cowl closure and oil cooler relocation.

Ron

[M20F-1968]

Let me throw this in for an idea.  I doubt that the increased air flow from the cowl flaps being open would cool the exhaust pipes sugnificantly given their high temperature and continued flow of hot exhaust.  However, it may be that the increased air flow from the open cowl flaps will cool the warmed air in the scat tubing that is slated to heat the cabin.  I would change the scat tubing to the double walled, and therefore more highly insulated, sceet tubing.  Hope that helps and works.

John Breda

[Bob_Belville]

45 minutes ago, M20F-1968 said:

Let me throw this in for an idea.  I doubt that the increased air flow from the cowl flaps being open would cool the exhaust pipes sugnificantly given their high temperature and continued flow of hot exhaust.  However, it may be that the increased air flow from the open cowl flaps will cool the warmed air in the scat tubing that is slated to heat the cabin.  I would change the scat tubing to the double walled, and therefore more highly insulated, sceet tubing.  Hope that helps and works.

John Breda

John, I'll be interested in whether that helps. I wonder if the mixer box on the front side of the firewall should be insulated? 

[jetdriven]

1 hour ago, M20F-1968 said:

Let me throw this in for an idea.  I doubt that the increased air flow from the cowl flaps being open would cool the exhaust pipes sugnificantly given their high temperature and continued flow of hot exhaust.  However, it may be that the increased air flow from the open cowl flaps will cool the warmed air in the scat tubing that is slated to heat the cabin.  I would change the scat tubing to the double walled, and therefore more highly insulated, sceet tubing.  Hope that helps and works.

John Breda

The exhaust pipes dont get cooled,  it's the muffler shroud cover and muffler which cools off. Specially a problem in a J model because the muffler is right in front of those two huge cowl flaps

[N201MKTurbo]

You could wrap the muffler shroud with header wrap. It shouldn't cause any problems because the shroud has continuous airflow through it. If you do try this, wrap it with lockwire after wrapping it to keep it from coming off.

[N811SS]

Hello All –

Good stuff, thanks for the dialog.  Here is an update on N811SS:

1) With the 201 mod on the M20F the air intake for the SCAT tube is just inside the front of the cowling on the pilot side next to the air filter. The oil cooler is relocated to the back of the top cowling on the pilot side.  I traced/visual inspect the SCAT tube integrity from the ambient air entry point to the cabin and all was good.  In the past I have had a similar situation mentioned above where one of the rods that actuates the cowl flap bangs into the SCAT tubing and rubes a hole in it but have since moved the SCAT tube slightly to provide clearance.  I removed the SCAT tube on-top of the heater box (a simple job since all you have to do is unscrew one hose clamp) and watched the flap that diverts the warm air flow between the cabin and the SCAT tube that exits near the cowl flap opening on the bottom.  Just as suggested above it was only moving about half-way open.  I re-adjusted so that the heater cable open moves it to full-open and diverts all the warm air to the cabin.  Eureka, it worked!  Now I have the reverse problem in that even with the heater cable closed about ½ the warm air still flows into the cabin!  For the winter months it is acceptable/preferable but come spring I am going to be bitching about it being too hot inside the cabin. Eventually I need to get a more permanent fix because it is very hard to move that cable through its full range of travel and the round flap inside that heater box looks pretty rusted.  Took a fair amount of lube on that cable and shroud even to get to function.  Also, with the number of twists & turns that cable/shroud does it makes it very difficult to push and pull?

 2) High CHT's is a bigger issue --> Amen to that!  Don't even get me started on all the issues I have had but in a nutshell I did an engine rebuild with Eagle engines 360 hours ago and never got those damn rings to seat correctly.  Never got better than a quarter every 3.5 hours, with CHT's running between 375-425 deg and wet plugs.  Basically it was a firewall wall forward redo with new cylinders + engine baffles + baffle seals replaced with every possible hole plugged.  50 hours ago I had all cylinders rehonned with new rings at the annual with the hope that this second attempt would get those rings to seat properly.  I think I have read everything possible on the correct Lycoming engine break-in procedure and we have literally followed the procedures to the letter.  Initial 3 hour break-in with high MP (like 28 inches or greater), low altitudes, no short flights, kept CHT's as cool as possible, do gradual decent using minimum of 21” and speed brakes, still running on mineral oil, etc.  Now, 60 hours later I still have the same issue as before the rehonning with burning a qtr. every 3.5-4.0 hrs.  Last borescope indicated wet plugs (but not real bad) on all four cylinders.  Since I am still supposedly in the "break-in period" I am trying to leave that cowl flap open basically all the time.  For the life of me I cannot figure out what I am doing wrong to this poor little IO360-A1A.  I have an Insight GEM and basically the CHT's and EGT's for all 4 cylinders are behaving the same.  Whatever the issue (glazing cylinders or annealing the rings) I do not think it is a run-of-the-mill problem.  My old Mooney does have a fair amount of mods like; electronic ignition in place of the left mag, three blade prop, stand-by vacuum system, airwolfe air-oil separator, modified cowling, relocated oil cooler, etc. but I doubt any of these could be contributing to my break-in problems, right?  After $32k for the rebuild and an additional $8k for the rehone-ring replacement I am beyond frustrated.

I know I am way-off the original topic but one thing that occurred to me was that perhaps the scat tube the exits the heater box is not long enough.  For example, there is about 8 inches of distance from the bottom of the SCAT tube to the opening for the cowl flap.  Maybe (and this is a big maybe) with the cowl flap closed the warm air exiting the scat tube from the heater box is helping to heat the space underneath the engine (instead of exiting out the bottom of the engine compartment) and contributing to high CHT’s and thus contributing to the ring seating problem?  Can anyone without a high CHT issue give me a sanity check on how close your scat tube exit is to the cowl flap opening?       

   

[jetdriven]

 I don't think any heat from the muffler or heater system is contributing  to your high cht issue. the air flows down  inside the cowl. 

 To stop your heater box from leaking hot air, u can convert to the 1979 in later style that has a flapper door valve inside, instead of the slide valve. if you seal that with some good silicone sheet on the flapper inside it'll be airtight no hot air leakage in the summer .

[Guest]

1 hour ago, N811SS said:

Hello All –

 

Good stuff, thanks for the dialog.  Here is an update on N811SS:

 

1) With the 201 mod on the M20F the air intake for the SCAT tube is just inside the front of the cowling on the pilot side next to the air filter. The oil cooler is relocated to the back of the top cowling on the pilot side.  I traced/visual inspect the SCAT tube integrity from the ambient air entry point to the cabin and all was good.  In the past I have had a similar situation mentioned above where one of the rods that actuates the cowl flap bangs into the SCAT tubing and rubes a hole in it but have since moved the SCAT tube slightly to provide clearance.  I removed the SCAT tube on-top of the heater box (a simple job since all you have to do is unscrew one hose clamp) and watched the flap that diverts the warm air flow between the cabin and the SCAT tube that exits near the cowl flap opening on the bottom.  Just as suggested above it was only moving about half-way open.  I re-adjusted so that the heater cable open moves it to full-open and diverts all the warm air to the cabin.  Eureka, it worked!  Now I have the reverse problem in that even with the heater cable closed about ½ the warm air still flows into the cabin!  For the winter months it is acceptable/preferable but come spring I am going to be bitching about it being too hot inside the cabin. Eventually I need to get a more permanent fix because it is very hard to move that cable through its full range of travel and the round flap inside that heater box looks pretty rusted.  Took a fair amount of lube on that cable and shroud even to get to function.  Also, with the number of twists & turns that cable/shroud does it makes it very difficult to push and pull?

 

 2) High CHT's is a bigger issue --> Amen to that!  Don't even get me started on all the issues I have had but in a nutshell I did an engine rebuild with Eagle engines 360 hours ago and never got those damn rings to seat correctly.  Never got better than a quarter every 3.5 hours, with CHT's running between 375-425 deg and wet plugs.  Basically it was a firewall wall forward redo with new cylinders + engine baffles + baffle seals replaced with every possible hole plugged.  50 hours ago I had all cylinders rehonned with new rings at the annual with the hope that this second attempt would get those rings to seat properly.  I think I have read everything possible on the correct Lycoming engine break-in procedure and we have literally followed the procedures to the letter.  Initial 3 hour break-in with high MP (like 28 inches or greater), low altitudes, no short flights, kept CHT's as cool as possible, do gradual decent using minimum of 21” and speed brakes, still running on mineral oil, etc.  Now, 60 hours later I still have the same issue as before the rehonning with burning a qtr. every 3.5-4.0 hrs.  Last borescope indicated wet plugs (but not real bad) on all four cylinders.  Since I am still supposedly in the "break-in period" I am trying to leave that cowl flap open basically all the time.  For the life of me I cannot figure out what I am doing wrong to this poor little IO360-A1A.  I have an Insight GEM and basically the CHT's and EGT's for all 4 cylinders are behaving the same.  Whatever the issue (glazing cylinders or annealing the rings) I do not think it is a run-of-the-mill problem.  My old Mooney does have a fair amount of mods like; electronic ignition in place of the left mag, three blade prop, stand-by vacuum system, airwolfe air-oil separator, modified cowling, relocated oil cooler, etc. but I doubt any of these could be contributing to my break-in problems, right?  After $32k for the rebuild and an additional $8k for the rehone-ring replacement I am beyond frustrated.

 

I know I am way-off the original topic but one thing that occurred to me was that perhaps the scat tube the exits the heater box is not long enough.  For example, there is about 8 inches of distance from the bottom of the SCAT tube to the opening for the cowl flap.  Maybe (and this is a big maybe) with the cowl flap closed the warm air exiting the scat tube from the heater box is helping to heat the space underneath the engine (instead of exiting out the bottom of the engine compartment) and contributing to high CHT’s and thus contributing to the ring seating problem?  Can anyone without a high CHT issue give me a sanity check on how close your scat tube exit is to the cowl flap opening?       

 

   

What type of cylinders does your engine have?

Clarence

[N811SS]

Eagle engines used new lycoming cylinders on it as part of the rebuild.  I think it was the standard steel barrels (but i am going to double check the color coding on top to see if has a blue strip indicating Nitride hardened).  I cannot find in the engine logbooks where it specifies.  Eagle went out of the engine business about 6 months after my rebuild.  It was a real mistake using them, should have gone directly to Lycoming.