I have a 12 year old bx2200 which has given me no problems until recently. When I went to do my annual service, I noticed that the coolant looked strange when I looked into it further, it smells like hydraulic oil. Bothe the engine and hydraulic oil levels stay constant. I drained and flushed the cooling system, and refilled it. After I ran it today for about 20 min when it cooled down, I checked the coolant again, and there are signs of hydraulic oil in it again. I can't seek anywhere that the hydraulics and the coolant would mix. I'm stumped, any suggestions