A couple of years ago we knocked a hole in the hydraulic cooler on our John Deere 310K EP and after the repair we refilled the hydraulic reservoir with Oreilly's Premium Tractor oil rather than the specified 15w40 engine oil. Yesterday we changed the hydraulic oil and it was yellowish in color. Under normal circumstances this would indicate that water has contaminated the hydraulic system but am not sure if color is from water or Oreilly's Premium Tractor oil. My plan was to operate with fresh 15w40 oil for a while then change oil and replace the filter again. Anybody have any thoughts or advice.
Water would make it milky. Probably just old and new different oils mixed. Some people will add a fluorescent dye to help pinpoint leaks.