Winter Flying

Flying in winter has many challenges:

• Hard starting
• Icy runways
• Rapidly changing weather
• Cold pre-flights
• Reduced daylight
• Icing
• Cold oil temperatures

....and advantages:

• Better performance
• Clear air
• Smooth air
• Less traffic
• Less heat stress on engine components

One significant consideration is oil temperature. After all, the oil must be warm enough to circulate freely and lubricate moving parts while not being so hot it boils off or loses viscosity. 

The answer to the "When is the engine warm enough?" will always be a compromise between "When the oil is warm enough to circulate and splash over moving parts" and the stress applied by running the engine on the ground waiting for the oil to get warm.

The Lycoming O-145 Operator manual has this bit of advice:

GROUND RUNNING and Warm-Up-- The LYCOMING O-145-B2 engine is an air pressure cooled engine that depends on the forward speed of the airplane o maintain proper cooling. Therefore, particular care is necessary when operating this engine on the ground. 

Avoid prolonged idling at low RPM as this practice may result in fouled spark plugs.

Limit ground running to 4 minutes in cold weather and ato 2 minutes at temperatures above 70 F
Note-- Engine is warm enough for takeoff when the throttle can be opened without back-firing or skipping of the engine.

"4 minutes" is not enough time (it takes me that long to taxi form my hangar to the end of 28), so I use 5 minutes from startup above 60 F, 10 minutes (or so) when it's below 60 F. Of course my engine is starting with an ambient temperature of at least 50 F since I use an Aerotherm engine heater set for 55 F.

Aluminum tape over oil pan blast hole

 I use Phillips 25W-60 XC Aviation oil year round. I also put aluminum tape over the oil pan blast hole in winter.

This seems to result in the best combination of oil heating, engine operation, and overall happiness.