Hydraulic's puking oil

[muddstopper]

I have one of the first ventrac tractors made. Hydrostatic, closed system. Lately, it has started puking oil back out the tank vent tube while running and will keep dumping the oil until the hydraulic level gets so low it wont operate. I havent started to trouble shoot to see whats causeing this yet and thought that I would ask where to start looking. Recently, I blew a hydraulic line and replaced it with a new one and that is about when this probelm started. At first I thought that maybe I had just overfilled with oil and that was what was causing it to overflow when it got hot. The next time I went to use the machine, the oil level was below the sight glass so I refilled and it would just pump it back out the overflow when running. I thought maybe air in system, but? I can fill the tank with engine off and cold and watch the oil level bubble down in the tank so I know the oil is going internal somewhere which should bleed the air from the system. I have tried filling with oil while the engine is running, it will take oil and then blow it back out the tank. To me it acts if air is trapped in the system, but I havent figured out a way to bleed it. I am open to any opinions or suggestions as to what may be causeing my problems, and if it just air locked, how best to correct it.

[J_J]

If your system is a totally closed hyd system, the same fluid and air will stay in the loop until you do a bleed procedure.

The bleed procedure involves cranking the engine but not running until all the air is bleed out. There should be a bleed port at the pump. if so, use a clear tube in a container , and look for air bubbles escaping utill you see no more.

On our Power-Tracs, I have a case drain and a pump housing drain, and the charge pump is continually refreshing the fluid that is sent out the case drains and pump housing.

Unless you bleed the air out, I believe it will stay in the system.

The air may be getting hot and expanding and therefore puking some of the fluid, as you say.

[muddstopper]

JJ, thanks for the suggestions.

I dont think the system is totaly closed, Ventrac just calls it a closed system. The fact that it has a tank vented to the air with no type of check would make it an open system. The tank just acts as a reservoir and only holds about a gallon of oil. Also, if air could get trapped in the system, then changeing the filter would introduce air to the system that would have to be bled out. I havent ever had to do that. Still, the oil gets white and foamy like air, maybe caused by cavitation at the pump. I still havent had any time to check anything, but am considering a complete oil/filter change for starters.

[wdchyd]

Muddstopper,

You have air entrainment (suction leak) from either a bad shaft seal on the hyd pump (if it is not submerged in hyd oil tank/reservoir) or loose suction hose/fitting....

You may have to use clean grease to do little tryouts if you suspect any spots........a bad shaft seal can be a bugger to figure out but the grease trick helps sometimes.....