I'm like ED I used to fly all year long but 40 degrees F is my break off point now days. When I was into control line and starters wasn't heard of we used to put the engines in the flow of the exhaust of a running car or truck to warm them slightly. 40 degrees isn't cold enough that a engine should not start if the batterys and fuel are up to par, remember the cold drains batterys faster that goes for the plane, glow starter and transmitter.