There are some risks to your ABC/N engines during winter operation.

One risk to an ABC/N powerplant in cold weather is exactly the same as the risk to a new ABC/N during break-in if it is run too rich -- the cylinder temp is not quickly raised to an adequate level & the piston-cyl fit at the top is quickly degraded -- this can occur in a fully broken-in engine in cold weather & the danger is greatly increased for a brand new engine. The consequence of such damage is that the engine's life will be significantly shortened. To avoid this type of damage, the upper cylinder & cyl head area should be partially shrouded to limit cooling, & thus permit operation at appropriate temps. This type of damage is not usually apparent for some time -- the engine seems to run just fine. However, its usefull lifetime will be shorter, as it is already on the way to wearing out. Those of you who run your engines during winter without carefull preparation, & think that they are OK, may very well be fooling yourselves -- the damage is probably there already, & will become apparent in the future. The colder the temp, the greater the damage.

The other risk comes from over-lean mixtures & this danger is greatly amplified at low temperatures. The resulting damage will very quicky ruin an engine -- one or two runs will do it. The "tuning band" becomes very narrow at low temps -- too rich & you accelerate the wear that is like an improper break-in -- too lean & you kill it much more quickly. The low air temp makes ignition more irregular & engines don't want to run well at a safe, but not overly rich mixture, unless some means is employed to raise cyl temps (shrouding, for example), which leads some modellers to lean out the engine a bit more until it runs well -- very dangerous practice.

For more information see the Oct 2003 issue of Fly RC magazine

_________________
Never take life seriously -- nobody gets out alive