Hey guys. I have a customer with a 1990 Maule M7 235. The cabin heat in the thing is almost none existent. He'd like to fly the plane more then just 6 months of the year. It has the extra muff on the tailpipe already, but we just aren't getting much flow. Any tips? Called tech support and they suggested I search online for answers.
Also, we are looking for a copy of the POH. I tried calling Maule for one and they don't print them. I'd have to buy an ATP subscription and print it off. Any one have a copy that I could get from them please?
Thanks.
David

Something must be wrong with the set up or it has massive air leaks around the doors.. I have melted peanut butter on the floor in the back seat area. Flow obviously isn't great on the ground but airborne should get great heat at or above normal cruise settings. I have the normal muffler cuff and the extra tailpipe cuff also. Blocked or kinked SCAT tubes? Are the slider plates moving fully open? Good baffle seals for positive pressure?

To get cabin heat to flow on a stock Maule set up you need to pull the “cabin heat” knob and crack the “vent” knob. If that doesn’t work reach out to Ty Wilkes at the Maule factory and he should be able to help you out.

Just went through this on my M7. A lot of small leaks can kill airflow. I think the biggest fix for me was 2 each stainless steel hose clamps around the heat shrouds On the mufflers. 4 total. Also did all knew scat. That alone increased the flow tremendously and I now have to turn the heat down. Too hot for my liking. Obviously make sure the slide doors are in proper alignment as well on the firewall. Beyond that these cabins are drafty if not taped at the wing intersection fairings and gear legs.

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FARMAULE wrote:Just went through this on my M7. A lot of small leaks can kill airflow. I think the biggest fix for me was 2 each stainless steel hose clamps around the heat shrouds On the mufflers. 4 total. Also did all knew scat. That alone increased the flow tremendously and I now have to turn the heat down. Too hot for my liking. Obviously make sure the slide doors are in proper alignment as well on the firewall. Beyond that these cabins are drafty if not taped at the wing intersection fairings and gear legs.

Do you mean around the heat shroud itself, or just on the scat hose? Glad to hear this isn't an anomaly. The guy at the factory didn't know and had no ideas on a fix. Glad to hear it's something that is fixable. Thanks for the ideas on where to start.

Around the heat shroud itself closest to each end. Mine had visible gabs between shroud and muffler assembly. No way to make pressure with a gap there. I used 8” but 7” clamps would have worked. Unfortunately I don’t have any pictures.

No pics needed. I'll give that I try. Thanks!

if setup correctly the cabin can even be too warm.
Start with engine baffling, is it sealing against the top cowl, are the two front baffles UP not DOWN.
Are the slide valves on firewall adjusted to fully open and close.
Heat should be a bypass valve, Freshair is a stop valve.
Are the heat muffs on muffler sealing or are they vibration cracked. Two turns of .040 safety wire or 7" hose clamps at each end or in middle will close the leaks (not too tight as the expansion is different for the aluminum versus the stainless steel.
Are the cutouts on inside of heat muff allowing free flow of air.
Are scat or sweet hoses crushed or kinked or torn or worn through.
Are the floor intakes clear and aligned with the hose fitting.
The heat and freshair and carb heat and brake lock controls on the panel can vibrate in to closed position if not set correctly. The knob should need to be turned slightly to activate in or out. There is a flat facet on shaft and ferrule for interference.

Now the cabin and doors.
Close off air ingress at landing gear gators and hinge line and wing struts to fuselage.
Insulate wingroots and behind 'elephant ears'.
Insulate above and beneath rear of headliner and floor and left side panel.
Silicone around the oval hole that door knob shanks move in.
Insulate above headliner especially at zipper areas. If porous headliner material it will seep cold air in.
Insulate under floor with something that will not absorb water or brake fluid.

It will now be warm.

FARMAULE wrote:Just went through this on my M7. A lot of small leaks can kill airflow. I think the biggest fix for me was 2 each stainless steel hose clamps around the heat shrouds On the mufflers. 4 total. Also did all knew scat. That alone increased the flow tremendously and I now have to turn the heat down. Too hot for my liking. Obviously make sure the slide doors are in proper alignment as well on the firewall. Beyond that these cabins are drafty if not taped at the wing intersection fairings and gear legs.

Another question for you. Does the smaller aux shroud that is just around the tailpipe blow right on your pilot feet? Or does it drop down through the floor and go way to the rear, under the middle seat?

The front heat is ducted from the slide valve to the right front of cabin at edge of kick panel. Part goes to the defrosters and part goes to right front footwell.
The other valve ducts heat through firewall then underfloor to enter either under the rear of pilots seat or under rear seat.
The aux heat from the tailpipe is ducted to a third valve on firewall and then ducted to wherever it has been directed in the cabin.
There are variations on used Maule's, as some have utilized the fresh air valves to reroute heat. It is easy to track the scat ducting to see where heat comes from and goes to.

maules.com wrote:The front heat is ducted from the slide valve to the right front of cabin at edge of kick panel. Part goes to the defrosters and part goes to right front footwell.
The other valve ducts heat through firewall then underfloor to enter either under the rear of pilots seat or under rear seat.
The aux heat from the tailpipe is ducted to a third valve on firewall and then ducted to wherever it has been directed in the cabin.
There are variations on used Maule's, as some have utilized the fresh air valves to reroute heat. It is easy to track the scat ducting to see where heat comes from and goes to.

This one only has 2 valves. The one from the aux that comes through the firewall between the pilots pedals then down under the floor and comes up under the rear seat. The other valve coming from the main muff comes through the firewall on the RH side and splits up to the defrost and copilot feet.
Yes its easy to trace scat tubing, just trying to figure out what the proper stock set up is. This plane has been rebuilt and if something was missed that is leading to terrible heat output I'd like to know. Sounds like it may be missing a valve.