I've added a radiator divertor valve setup to my 912S along with an in cockpit heat exchanger fan combo. Now I can totally divert all the fluid flow away from the radiator on my Rotax 912S to hasten warmup in cold weather (for the engine and for the cockpit), and do it in a way that makes practical use of the diverted heat. Once climbing out or descending from altitude, it is a simple matter to adjust the valve position (panel mounted control) to achieve pretty much whatever temp I want. I caught myself a few times this weekend opening my air vent as it was getting too warm! Then I wised up and shut the fan off.

The muffin fan comes on automatically at 110 degrees, (via a thermal snap switch) or can be manually controlled via a three position switch. I still have full use of my pre existing muff heater, and even with the drafty S-7 cockpit it has gotten pretty cozy, more importantly I now have much quicker warmups, and can keep the engine in the sweet spot temp wise whether cruising at altitude followed by a fast descent, or high AOA slow flight with high power settings later in the day as it warms up. No more duct tape! Installation will vary on your bird, mine was easy, a half day or so.

The guy who set me up with it: S-7 builder/modifier/flyer Joel Milloway, can be contacted at [email protected]

Tom, that is interesting. That is a mod that I would consider incorporating into my CH750 - 912 build. Would like to see more photos, especially the installation.
Thanks, Joe

Pretty simple Joe, though everyone's would be different of course. The valve goes on the pressure, or supply, side of the waterpump, in my case a few inches before it enters the radiator, the 5/8" line goes through the firewall and to the heat exchanger/fan unit, which in my case is right under my panel between my knees in otherwise dead space: it is not in the way at all, even with the biggest boots I wear. The return line goes back through the firewall to a 1" x 1" x 5/8" tee (Rotax uses 1'' for their main circ lines) and the circuit is completed.

My snap action thermal switch (Graingers etc, less then 20 bucks) was mainly used because I already had some in the shop for my hot water solar projects, and it works the same here. The thermal switch is simply held in position (for good heat transfer) against the metal incoming fitting, and when it warms up the fan starts, and when it cools down it shuts off. Not really needed, but I like the auto feature, my woodstove fan does the exact same thing.

Mine was an afterthought, planned ahead I could have left an even more out of the way place under the panel, or even alongside the left or right side of the boot cowl. Although I already had a heat muff system in place, and left it there at least for now, you could go with this for your main heater and forgo the muff. Joel also mentioned a tuned exhaust for the 912S he is working on, it provides more power but is not so easy to put a heat muff on, that led to this hot water cabin heat setup. Hey I like having TWO heaters... I can always open a door if it gets too hot!

Plus you can just have the new heater unit in bypass, which will keep it from turning on!

Tom, if it has been in "bypass" but you are already flying, how long would it take to switch on once you diverted hot coolant? Just so I know how to work my heater when that tuned exhaust becomes available

emflys wrote:Plus you can just have the new heater unit in bypass, which will keep it from turning on!

Tom, if it has been in "bypass" but you are already flying, how long would it take to switch on once you diverted hot coolant? Just so I know how to work my heater when that tuned exhaust becomes available

It will of course depend on how hard you working the engine, and ambient temps, my first flight it was 9 degrees. There seems to be a bit of a lag, as the snap switch is not immersed in the fluid, or even making full contact with the aeroquip fitting as it enters the cooler, so it is not as "right now" as you'd think. A few minutes?? I just ziptied the snap switch (the part you want in contact is about 3/4" in dia., the whole thing the size of a quarter), to the fitting, and then ziptied some foam weatherstrip over that to kind of insulate the sensor. It works well enough to be worth doing I guess, like I said I had one right in the workbench drawer, so what the heck I thought I'd use it as a trick little feature.

I am going to put a bug into Joel's ear about how I want a tuned exhaust also, but don't want to give up my swiss muffler, that'll mess with his head! It MAY even be doable.