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Hi Jim. I'm taking for granted that you have the correct amount of fluid in the system as either too much or too little can cause cavitation, which could produce the symptom you describe. Second, it seems unlikely that a misadjustment by itself would cause a problem to show up ONLY after the fluid warms up. It would likely be a problem ALL the time. You have most likely already picked up on WHAT generally is the problem. Narrowing it down to the specific problem part(s) is what needs doing now. If you haven't already done so, what I would try first is to run it until it warms up, without putting any load on it at all and then raise and lower a load, such as your box blade, to see if the problem is any different then from when you're working. If no difference, at least you know that some sort of kickback into the hydraulic/mechanical parts from the ground contact isn't complicating your diagnosis. Based on personal experiences with varying degrees of worn parts and mysteriously failing hydraulics, both 3 pt. and steering, it seems likely that what you have is a leakback situation in the pressure side of the hydraulic circuit which worsens as the VISCOSITY of the fluid decreases when warmed up. This could be caused by several things, some cheap to fix, others quite expensive. My best guess would be that either the seal(s)hardened up from sitting too long or that there is some rust/pitting in the hydraulic cylinder that chewed them up when you first started using it or both. Fixing it MAY be as cheap and simple as: 1: replacing your fluid with a heavier wt. fluid (if the fluid that is in there now is too thin for even new parts to hold pressure it will act that way whenever it warms up); 2 tightening a loose or cracked internal connection; 3: clearing the filter to stop cavitation; 4: getting new "o" rings and piston seal(s) to seal internal leaks; 5: a light honing of the lift cylinder. If you get past all of those cheap and straightforward things without curing the problem, it is likely to be expensive. As encouragement to you, I'm currently using a Ford 2000 diesel that had a COMPLETELY non functioning 3-pt lift when I got it (mainly for its commercial ft end loader). This one also sat a year or more. It really only needed a thorough cleaning out and degunking of the hydraulic fluid and filter, some elbow grease and a light hand honing of the hyd. cyl. bore and a new piston seal to fix it, but since it was apart anyway, I had grease fittings and new bushings put in the cover for the rockshaft. One piece gaskets are a pain for a heavy cover such as the Ford uses, but having just removed a large quantity of silicone caulk type Form-a-gasket from the pick up filter, I chose not to repeat the experience anytime soon and used a stamped gasket. This one still has a small amount of leakback, but it really only shows up significantly when I'm hauling a water tank (1200#+) and running at low engine speed.
good luck
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