That is significant disadvantage of a hydro transmission for cold-weather use. With gear, I cant feel any temperature effect. The tractor just goes at the same speed, if it is -30 or 95 degrees when I let out the clutch, dependent only on gear selected and engine rpm. The only trouble is the lift hydraulics which takes a little while to warm up when it is real cold out. On my old 8n Ford, with straight 90 weight oil, I would have half my plowing done before the rear blade lifted at a summer-like speed. Thankfully, my newer JD with multi-visc oil, starts out cold at a half-way decent lift speed. If only there was a way to take the temperature-dependency out of the lift mechinism. I guess a manual lift would do that and also eliminate the need for a gym-membership and cab heater.