I have a Reiff system on my 9A as well, and it works great in the Michigan winters. However, there are some compelling arguments for not keeping it plugged in 24/7 (depends in large part on how often the aircraft is flown).<snip>
I was wondering how long it would take for the questions to arise about 24/7 heater use.
How to use an engine heater is not as simple a question as some might think. As Terry mentioned, heater use depends a great deal on how often the plane is flown. Below are some of my thoughts based on nine years of sump heater use on my RV-6 and continually researching anything I can find on the subject.
1) Lycoming and Continental do not officially condone the use of engine heaters 24/7. For some pilots, that is reason enough to not use a heater on a continuous basis.
2) The reason for concern about 24/7 heater use is the accumulation of moisture in the engine. That is a valid concern and none of us want our engines to rust internally.
3) Moisture accumulates in the engine from water trapped in the oil during combustion which collects on engine internals when there are temperature differentials within the engine (warm oil/air, cold engine).
4) The reason I justify 24/7 sump heater operation on my plane is threefold:
A) My plane is flown at least once a week (addicted to Saturday morning pancakes.....). It is my opinion that weekly flights are sufficient to prevent the onset of corrosion because this doesn't allow oil time to vacate internal engine surfaces so corrosion can get started.
B) It is my opinion that maintaining the
entire engine at a temp
above the dewpoint is the best way to avoid temperature differentials in the engine that promote condensation. My engine doesn't know winter exists since it thinks warm weather reigns year round. When the plane is returned to the hangar following flight, the heater is plugged in and the engine stays warm all winter just as it does the remainder of the year. In my climate, a blanket over the cowl and inlets plugged will keep oil temps near 90 F and CHT about the same. This means the entire engine is heat-soaked. The heater has a thermostat that limits oil temp to 150 which is plenty cool to prevent degrading or coking of the oil.
C) I had the opportunity to pull a cylinder (sticky valves). Since the heater had been used for four winters, I made a concerted effort to check the condition of cam lobes and lifters and could see no indication of any corrosion, the internals of the engine were pristine.
In summary, I use a heater 24/7 because I want the entire engine to remain at a stabilized temp above the dewpoint for the duration of cold weather, and my plane is flown frequently which I think also prevents the possibility of corrosion.
In my opinion, cycling a heater with a timer between flights is the worst possible scenario since it creates a favorable opportunity for moisture released from the oil to accumulate in the engine due to temperature differentials.
My conclusions won't be appropriate for all situations, so as they sometimes say......your mileage may vary.