I have A Case 621D loader with 5500 hours that I have owned for a year. The power steering and lift arms/tilt lock up in cold weather (less than approx 10 degrees F). The loader works fine after coming out of a warm building after about 30 minutes in cold weather I all of a sudden loose hydraulic function of the steering and lift arms/ tilt. If I turn the key off and restart it everything functions normally for a few minutes then it does it again. Sometimes it works for a while. Sometimes it will do it 5 times in a row. The oil level is good. I drained out some of the hydraulic oil out into a bucket and it looked really clean, no sign of moisture. I have the service manual for this machine. I have ordered a hydraulic test coupler but do not have it yet. I am using case hytran oil. ( i do not know what the previous owner used). The filter only has 500 hours on it. I have not changed it yet. Thanks for any ideas!
It sounds like that you have a hyd. lock out solenoid relay problem check that.
Thanks for your reply. It seems that the soleniods were functioning correctly. I'm pretty sure the hydraulic pump was just starving for oil. We drained the hydraulic oil and replaced it with hytran. Also replaced the filter. I also opened the access cover on the tank to check the suction screen. The screen was not plugged but i removed it anyway and blew off a very small amount of debris. I delt with this problem for a long time because the dealer told me that there was no section screen. So in my mind I felt that since the pump is fed with a 2"? line it could not actually be starving for oil. Im pretty sure that in really cold temps the oil was just too thick to pass through the screen. I have only owned this machine for about a year so I have no idea what oil it had in it when I purchased it. It has been operating fine so far but we have not had any really cold temps since the fluid change to really know for sure.
I'm glad that is all it was
If it does it again, I'd be looking for a suction air leak. or collapsing suction hose.