Corrosion
OK Folks ….. I’m going to go out on a limb here regarding the corrosion issue and say heated or unheated, the corrosion issue would be minimal in the Rotax engine as installed on the RV-12. I may be all wet about this, but I feel the ideas mentioned thus far need to be narrowed to the Rotax engine specifically.
My reasoning is based on my belief that the Rotax oil system is a closed system …. in that, there is no direct venting on the Rotax crankcase directly to the atmosphere as opposed to a traditional aircraft engine, which vents directly to the crankcase of the engine. This is a BIG difference. Thus, it would appear to me that it would be very difficult to develop significant moisture deep inside the Rotax engine once the oil has been above 212 degrees for an extended period of time … because at that point, there is no moisture inside the engine and no direct path for atmospheric moisture into the crankcase via a crankcase vent tube as there is with a traditional engine. Because of the location of the Rotax oil tank in the RV-12, the oil lines between the oil tank and engine isolate the atmosphere presented to the oil tank from the vent line … thus preventing atmosphere from directly entering the Rotax crankcase because residual oil in the oil lines block the direct path for moisture to get inside the engine’s crankcase from the oil tank.
Of course, as with any standard aircraft engine, there is a path for moisture to get into the cylinders through open intake or exhaust valves. To my way of thinking, the potential corrosion areas would be any exposed cylinders themselves, the heads or tops of the pistons … as it would be for any standard aircraft engine. Seemingly, the majority of the internal engine components such as the crank, rods, cam, push rods, lifter/rocker arms, valve stems, and the clutch/gear reduction unit would, by in large, be spared from corrosion due to the lack of direct contact with the atmosphere.
As such, I suspect the use of a block and oil tank heater on the Rotax will be beneficial overall for starts in really cold weather without the worry of creating an atmosphere for corrosion developing deep inside the engine. For the Rotax, guessing turning on the heater the evening prior to a desired flight would be sufficient to minimize the moisture buildup inside the combustion chambers of those cylinders with open valves.
The above is just a theoretical guess on my part and not based on any conclusive testing. I would be very interested in hearing what others think about this. Perhaps one of the more experienced Rotax mechanics can offer some real world experience to the topic.