Engine pre-heat condensation thoughts

[AlexPeterson]

This is side branch of another thread regarding cell phone/pager remote heater operations.

Bob M. asked a question regarding possible down sides to 24/7 engine heating, and relayed their group kicked it around and said it could drive moisture into the oil sump.

Water liberated by heat in one area of the engine will drift towards and possibly condense in other colder areas of the engine. (This is an important process, as it is how a whiskey still works!)

So, when hot air is blown into the cowl, the cylinders clearly heat first, liberating moisture from those. The oil sump will take much longer to heat up, so yes, moisture probably does migrate to it. How much moisture is present in the cylinders to do this? Wouldn't seem like much.

The potential issue with heating only the oil sump is the opposite - moisture liberated from the sump condenses in the cylinders, which are constantly being cooled by convection of air moving through the cowl.

From a scientific point of view, heating the whole engine uniformly is what is desired. Any sort of heater in the lower cowl, preferably on a thermostat, is a good idea. The cowl needs to be reasonably sealed and blanketed. I use foam plugs in the inlet/outlet areas, and a blanket around the whole outside of the cowl. The entire cowl is then uniformly heated to 70F, for example, if a thermostat is used.

I put a hobbs like counter on my engine heater one winter to see just how much it ran in a 45F hangar. It ran about 1/3 of the time, costing perhaps $6/month, with the thermostat set at 70 under the cowl.

[Ron Lee]

I don't know the answer but my conservative response to my ignorance is to only use the oil sump heater when I plan to fly and always start the engine when I use the oil sump heater. The engine dehydrator should eliminate any concern.

[guccidude1]

Several years back (4), I purchased a Tannis engine heat system for my C-182, Continintal O-430 engine. The Tannis representative wouldn't sell me just a sump heater because their research had indicated that heating the sump only created moisture in the engine. I bought the recommended system which consisted of a heater pad for the oil sump and a pad for the top of the case plus a metal heating element that bolted to each head (6) near the intake tube. The representative's recommendation was to not heat the engine unless it's going to be flown. Just one more piece of info for the puzzle of knowledge. Dan.