From Al:
I live in Central Texas where most years if it freezes it may go to 20F overnight. I am also in a T hanger but it has no heat. Has anyone used a drop light located in the lower cowl with a 100 watt bulb to keep things warm. I know this will not keep the battery warm or charged but might help the oil a bit. Any experience with this? Could it cause oil runoff? Will it cause internal engine corrosion?
If you hang any kind of heat source under the cowl that is capable of charring cloth or paper (such as a 100-watt light bulb), be absolutely certain that it is located in such a way that oil cannot drip onto it. It is common for cold oil that is clinging to some surfaces to become liquid enough to flow and drip on a heat source.
A hot light bulb can certainly help a lot. It will help the most, and be most safe, if:
1. Cowl plugs are in, a heavy wrap is over the cowl (like an old rectangular sleeping bag), and the heat source is below the engine.
2. A drop light is used that has a metal shield (rather than plastic), and the light is positioned so that any drips will fall on the shield. It won’t get hot enough for ignition, but it will radiate most of the heat beyond it.
3. The heat source is applied right after a flight (and left on), so that it is maintaining warmth rather than trying to reheat a chilled engine.
Some people claim that ongoing heat will cause water vapor to separate from the oil, leading to internal corrosion. I understand the argument if an engine is parked with “wet oil” following a ground run-up, allowed to chill, and then a heat source is applied (but without flight). That could lead to the oil warming up before the rest of the engine. If any water vapor separates from the oil, and then condenses on colder surfaces, corrosion can form.
Having said that, I don’t see how it can happen if an engine is parked after the oil has been thoroughly “dried out” through at least a 30-minute flight at 180 degrees (or higher) oil temp, and if the engine is continually maintained at a temperature that is above ambient (no matter how slight). Moisture cannot condense on a surface if it is warmer than the ambient dew point. At any rate, I am a big believer in keeping an engine slightly warm all the time. The OWT that claims that warming causes residual oil to drain off surfaces faster has been thoroughly debunked by the oil companies and independent tests.
Note that there are some good posts in BAC regarding highly effective small chargers that will not only keep your battery warm and charged, but will both prevent and reverse sulphation over time.