I agree with bcorradi. If it's cold out, I'll usually mess around with some light branches or something for a few minutes to bring the saw up to temp. After the saw has been at temp for a few minutes, even the heavy summer bar oil is pretty fluid in the tank. On older bars and chains that I'm not too worried about, I have run atf or kubota SUDT2 that has come out of my tractor before and they both worked very well in the cold.