I've got a new to me 2021 BX23S with 155 hours on it. Purchased it used a few weeks ago from a local dealer, and it is my first tractor.
I didn't get any information or history on it. The factory painted grey filters were still installed so these fluids are factory fill. I'm assuming it was purchased and used, then left to sit. I decided to change all the fluids and filters out seeing as they are all four years old. I warmed up the tractor and started draining the hydraulic fluid and was quite surprised to see what came out. The fluid had a greenish black tint to it, had some small bubbles in it, and smelled pretty awful. It seemed a little thin but wasn't slimy. The filter was very heavy and the element was very dark. It did not have any buildup and the metal was all shiny. The strainer had a slight film on it but it wasn't blocked.
I cleaned the strainer, put on a new filter, and new SUDT2 fluid in. Everything feels much better. I don't think there is any damage as I did not see any metal flakes or brown/rusty pieces in the fluid. After the fluid and filter change all the cylinders feel strong and drive/reverse feels strong as well. No loud or strange mechanical noises.
I'm mostly wondering what happened to the fluid. I'm new to hydraulics, but I think it is water contamination? If so, is this something that is to be expected when a machine just sits for four years? Should I be looking for anything else that could be wrong to cause this?
Thank you.
Photo of the tractor and a couple of the old fluid.

I didn't get any information or history on it. The factory painted grey filters were still installed so these fluids are factory fill. I'm assuming it was purchased and used, then left to sit. I decided to change all the fluids and filters out seeing as they are all four years old. I warmed up the tractor and started draining the hydraulic fluid and was quite surprised to see what came out. The fluid had a greenish black tint to it, had some small bubbles in it, and smelled pretty awful. It seemed a little thin but wasn't slimy. The filter was very heavy and the element was very dark. It did not have any buildup and the metal was all shiny. The strainer had a slight film on it but it wasn't blocked.
I cleaned the strainer, put on a new filter, and new SUDT2 fluid in. Everything feels much better. I don't think there is any damage as I did not see any metal flakes or brown/rusty pieces in the fluid. After the fluid and filter change all the cylinders feel strong and drive/reverse feels strong as well. No loud or strange mechanical noises.
I'm mostly wondering what happened to the fluid. I'm new to hydraulics, but I think it is water contamination? If so, is this something that is to be expected when a machine just sits for four years? Should I be looking for anything else that could be wrong to cause this?
Thank you.
Photo of the tractor and a couple of the old fluid.


