This may not be directly applicable to most engines people are flying these days, but as a matter of academic interest, let's not forget two more techniques fairly popular in the past:
- If the engine has an easily accessible drain cock, drain the oil while it's still warm, come back next morning with a pail of preheated (+50...60C) oil.
- At the time of shutdown, dilute the oil with avgas. While you are starting the cold engine, this will reduce the oil viscosity; as the engine warms up, the fuel will evaporate and the oil will return to its normal viscosity. Radial engines are often equipped with an oil dilution valve directly in the fuel system. Many winters ago, when it suddenly got as cold as -30C, I used this technique on my
UAZ. With undiluted oil, the starter would barely crank the engine even with a warm battery, so it had to be towed for a few minutes to get started. A cupful of petrol into the oil in the evening would allow me to start in the morning without any problems. (Once again, this should not be construed as an endorsement of this method unless allowed by the manufacturer; Lycoming
explicitly discourages it).