if the oil(fluid)is getting hot that quickly without working it you definitely have a restriction problem.You may want to even just go ahead and replace the valve,it might be a unidentifiable old closed center valve or something that doesn't belong on the machine..A closed center valve backs the pressure up against the relief in the valve body until the (handle)spool moves then the system works against the load. Very common on farm tractors and such,it responds quicker than a open center system..Each system has different valve designs.An open center valve continuously moves oil thru the system,until the valve spool moves then the oil goes to the work and backs up against the work or load until the system hits the relief valve pressure..sounds like you might have the wrong valve installed..just a thought. SurplusCenter (IMHO) has the best deals and selection on valves. I just got a spare pump for my mini articulated loader there,two section pump for about $75..hard to find pump too..I shoulda ordered a spare when I first built it. Thier website has a lot of useful tech info on hydraulics there as well. Best of luck. Merry Christmas,yes Im not afraid to say it.
