Winter can be a beautiful time to fly. Cold stable air makes for smooth enjoyable rides. The ASOS was reporting a density altitude of -1500 ft the other day. But to enjoy the flight you have to be able to stay warm and the engine needs to run warm enough to prevent maintenance problems. Flying without getting the oil temperature into the green or CHT's in the low 200's is not a recipe for long engine life.
Maules are not made with cold weather flight in mind. The factory has no winter kits designed or available. First bit of advice is to dress as if you were going to have to walk home and have a survival kit for your terrain and climate. To use my airplane year around I had to come up with some minor mods to improve the situation.
One of the easiest things to do is to tape off all or a portion of the oil cooler fins or the ducting going to the oil cooler. Do a test flight to see how the oil temps react. On my MX7-160 when the OAT is close to O degrees F I block off all the air flow to the cooler and the oil temperature struggles to get to 160F.
You can spend time working on the door weather stripping and try slowing the flow of cold air into the cabin but there is only so much you can do. I decided to see if I could make the heating system work better. Looking at a Cessna 182 I saw the heat can was studded to give better heat transfer. Depending on your set up you can add an auxiliary heat muff on the tail pipe to provide warm air to what is normally the cabin ventilating air duct. Depending on your set up, the back seat heat can redirected the to the front pilots side.
Limiting the amount of air through the engine also helps keep CHT's and oil temperatures up. Again looking at Cessna winter kits I built some covers for the front cylinders. I have a 6 point CHT gauge so by flight tests I was able to see the effects of the covers and how much air is needed to flow through the cylinder. At the bottom of the cowling I built a plate to block some of the air flow through the cowling. This acts as a fixed cowl flap. By doing this it also seems to put more air flow through the heat muffs and helps the efficiency of the system as a whole. I use this when I will be flying in below O degrees F temperatures. If I fly into much warmer air I often have to land and remove the plate. The best option would be a movable cowl flap system.
Below freezing to O degrees F may be to warm for the bottom plate to be installed but the oil temperature will be running low even with the duct tape on the oil cooler. My M6 has an updraft carburetor. The oil cooler sets below the air filter intake and gets air flow from a whole in the cowling below the prop. There is an air duct to force the flow over the cooler. When the temperatures start to decline in the fall I remove that duct. Now the air flow is not directed directly on the cooler and that seems to help bring the oil temperature up. If I need to warm the oil even more I block of the inlet under the prop. Now only the warmer air circulating in the cowling acts to cool the oil. The air now being drawn into the carb is also warmer and seems to help the fuel to volatilize better and be distributed through the induction plenum more evenly. This helps the EGT's to be more even. This will also make the intake air less dense. Sort of like flying with partial carb heat on. There will be a slight loss of power but with the low density altitude of the cold outside air aircraft performance does not suffer.
I bought my first Maule in 1993. Over the years the aircraft has proven to be rugged and reliable. I have learned a few things along the way that might help you avoid some of my mistakes and expenses of owning and operating an aircraft.