656 gasser oil pressure

What is a good oil pressure range for a 656 hydro with a gas engine. Mine runs about 35 at a cold start and then drops to about 31-32 during warm idle (6-900 rpm). At warm PTO speed it runs about 32-34. The engine has about 5100 hours but the guy I bought it from told me they went through the engine not long ago however he was pretty vague about exactly when and what they did to it because he said his son did all the work. He said he didn't remember the hours because they had been only using the tractor as a spare loader tractor for years and it got very little use the last few years since the work was done. It purrs like a kitten and doesn't seem to use any oil other than what leaks from the valve cover and other small leaks. The hydro is a little weak in forward but it works great for haying and loader work. One thing I found very soon after buying the tractor is that the hydro starts to slip almost as soon as the oil level gets a little bit below the full mark. I changed the oil and filter right away and that also made a huge difference. The hydro pressure went from 1800 in forward and 3500 in reverse to 2800 in forward and 5000 in reverse. The seller told me he had never changed the oil in over 20 years because it looked good and they always added new oil. Don't know how many hours the old oil had but I'd bet it had to have a couple thousand hours on it.

Can't speak for the hydro pressures but the engine oil pressure sounds normal to me. These engines even with lots of hours will hold about 30-35 psi hot, cold, idle or WOT.

If the engine oil pressure is staying about the same under the varying conditions, it is an indication that the pressure relief valve is controlling the pressure at all times. That is a sign of a healthy oil system.

If a little drop in oil level in the hydro is making that much difference I suspect that you are not using the correct procedure to check the oil level. On the Hydro tractors, the oil level is to be check with the engine running. It needs to have been idling at least a couple of minutes before checking. On the Hydro tractors the Hydro transmission housing is kept completely filled while in operation. This will cause the oil level on the stick to drop a couple of inches after the engine is started. That is why you need to have the engine running to check the transmission/hydraulic oil.