Over the 4 years I've owned the tractor, I've used NAPA hydraulic filters. I would say that I've never had "good" hydraulic flow rate judging by what I would consider a slow 3 point and relatively slow Koyker 155 loader (with 6' bucket).
Over the winter this problem has become significantly worse. I pulled the screen which was clean. I replaced the hyd filter. I replaced the UTF with Coastal JD303 (actual name of product) from AutoZone. While I had the tractor drained, I pulled the hyd pump hoping to get it "bench" tested. Instead I had it inspected for wear and it got a clean bill of health (however I'm not sure how accurate the shop's assessment was).
When the job was complete I had some difficulty priming the pump. I tried inclines and declines trying to get the fluid to the pump. Even after what seemed like a fair prime, the 3 pt and loader were sluggish to non-existent at low rpms. I also noticed hissing/crackling at the pump that I now suspect as cavitation due to poor suction flow. It was at that time that I remembered some talk on this board about NAPA filters not always being the correct exchange for the Yanmar filters.
I took to drastic measures this weekend. Before ordering a genuine replacment filter, I wanted to prove to myself that it could be the filter. I pulled it and the filter mount and bypassed it with 1" ID clear PVC tubing. Here comes the good with the bad . . .
Once primed, the hyd pump noise went away since it was no longer starved, however, with loader detached, the 3 point wouldn't move at low idle. It took rpms >2000 to get it to move.
Without being familiar with the fluid flow once it leaves the visible output pump lines and goes into the tractor, I have to suspect that either the pump is damaged or I may have a restriction somewhere in the tractor (maybe at the speed knob valve under the seat).
Are there other full proof ways of measuring hydraulic performance? I'm not sure what to do next. Can a typical hydraulic shop rebuild this pump (if it's bad)?
