I have a 7745 that the hydraulics stopped working on. I have always used the 80/90wt oil in it and had no problems even in cold weather. Nite before last I checked it and was a little low so I added a gallon. Next morning(20 deg F) and now no hydraulics at all. This is very thick oil for this temp but like I said before, it has never been a problem. It almost seems as if the pump is not running. Any chance the heavy oil broke something? Any other advice greatly appreciated. Thanks