Took some out there is no sign of water...it seems to be air. Any idea how air could enter the system? Can find any leaks.
It looks like air to me too. Microbubbles. Water is usually more opaque - it really can look like dirty chocolate milk.
Air goes away pretty quickly... The tainted fluid appears to rise up because the microbubbles make it less dense than the clearer de-aired hydraulic fluid. I've never timed it but that process takes hours rather than days.
Water takes days if it separates at all. Depending on detergency, sometimes it either doesn't separate or takes so long that I've gone on to other projects. If it does separate, I would think that the clear amber hydraulic oil is less dense - most oils are not as dense as water - and should float on top of the water.
As someone said, the only way air can get in is from the suction side - basically that means it has to be getting in somewhere along the path that starts at the bottom of the common transmission/hydraulic sump and continues up to the inlet to the hydraulic pump.
Typically that path will go from a cleanable crud filter inside the sump, out through a fitting on the bottom of the sump, up to a spin-on replaceable filter or even two spin-on filters in series - and from the last filter it goes directly to the hydraulic pump inlet side.
The suction line can be a rubber line although more commonly it is a steel line with compression fittings. We do see leaks sometimes associated with pinhole damage to the wall of the suction line itself, but by far the most leaks are in the end connections rather than to the line itself.
Look for suspicious places from the suction line as it exits the sump and goes to the filter, or from the filter to the inlet to the hydraulic pump . It is rare for the leak to be within the pump itself. Although I've heard of leakage past a rotating shaft seal and into the suction side of the hydraulic pump, it is fairly rare.
Don't even think of looking inside the pump itself until you are positive the suction leak isn't in the suction line or fittings.
HOW TO FIND A LEAK:
IF the suction leak is happening below the top level of the Trans/Hydraulic Fluid (THF) in the sump, then it will almost always be able to be seen as a wetness around the leak after the tractor has sat overnight. Wash it, let it sit, and look. That is where most are and how they are found.
If that doesn't do it, work your way up to the pump renewing connections and/or lines until you find the problem.
If it is the pump, take it to a rebuilder.
Good luck,
rScotty
