Well if your looking for a real cold temp to fly in, come on up to Canada. Up here in the northern part of Alberta we go by a general temperature rule, -5c is good but below -10c is not. Most engines do not have a problem with the cold but if you want to keep some heat in the engine once your air born, try putting some aluminum foil around the front of the cooling fins, this seems to work good up here in winter and the engines work great. But also you must consider that most balsa wood does not like the cold, it becomes very brittle after -5c. So check you temps and see whats good, we fly all year round up here just depends what the weather for the day is like.