Thomas 85 skid steer - A hydraulic line blew back in the summer and the local repair shop made repairs to get it working again. Since then though, the skid steer has had a bad habit of locking up. I'll run it for 20 to 30 minutes, put the boom down to scrape dirt or manure, then when I try to lift the boom it's locked in the down position. If I don't get the tractor to a safe area (out of the barnyard) quickly, the drive motor will also lock up. With the unit in a safe place and turned off, I open the back and have a look in the engine compartment to see if anything appears wrong. The only thing I've noticed is that the hydraulic oil level in the sight glass is either completely full, or just a 1/8" gap at the top. Is it possible for the hydraulic reservoir to be filled too much? That is, if filled to the top of the tank, and the hydraulic fluid heats up and expands, would the increased fluid pressure on the control box relief valves cause them to trip? Or is it probably something completely different? BTW, if I leave the T85 parked for a while (last time it was overnight), upon restart everything is working fine: well, untill the next time it locks up.