Don't know for sure how your hydraulics are set up. I had a tractor recently that the hydraulics acted up. I had no loader, no 3 pt arms and no power steering. You would of thought there no hydraulic fluid what so ever in the tractor. Hydraulics can act funky in the cold. Usually I can start working the steering wheel, loader, and 3 pt arms and get things going. However, it was about 15 below zero and I had big problems. There are valve bodies, relief valves,the pump, the hydraulic lines and so forth. I started "cracking" hydraulic lines starting with the line feeding the pump. What ever the problem was, cracking the lines got me going. Every thing started working gradually. after working all the hydraulic controls on Every thing for about 10-15 minutes everything started working. I mean I would raise the loader 3-4 feet and lower it back down. Then raise it again maybe a little more say maybe 5 feet and lower it again. I eventually got everything working like it is supposed to. Don't know if this is you problem or if this will solve your probem, but it maybe worth a try.
