Cold weather is upon us. Although it was published in 1979, I encourage everyone to take a look at Advisory Circular 91-31c: Cold Weather Operation of Aircraft. To this day it is still listed as reference reading material in the Practical Test Standards under engine start procedures. The advisory can be downloaded on the FAA's website here:
More information concerning engine operation is available in Lycoming's Key Reprints - Operations
Lycoming Mentions several useful bits of information for cold weather.
- Check for a frozen fuel selector valve prior to start.
- Because more fuel is required to get the right mixture in denser air, more primes will be needed for start the colder it gets. Trial and Error
- If the engine fires but fails to start and fails to fire on further attempts, a preheat may be needed. The water vapor created by the burning gasoline can ice over the spark plugs. They will not spark again until thawed.
- Preheat should be required in temperatures less than 20 F.
- Try to avoid shock cooling of the engine (less than 50 F temperature change per minute). Reduce power gradually on descent, and allow the engine to warm up prior to takeoff. Shock cooling can lead to "power-off letdowns".