Have a cat 973 puking hydraulic out of what I think is a vent near rear of engine. Just behind the rear of the engine is a section that the starter bolts to which I would call the bell housing. At the top of this section on the right side is what I think is a vent and when the engine is revved up hydraulic fluid comes out of this vent. The next section toward the front of the machine has a filler neck and a dipstick and the next section has a filler neck and a sight glass. My question is if the section directly behind the engine is supposed to have hydraulic and if so why is it coming out of the vent?
Have you had to add oil to the gear box or hydrostats? It is hydraulic oil and not motor oil right? There are a couple of o rings on the shaft going into the gear box that could be leaking. The rear one with the sight glass is the drive pumps or hydrostats. When cold it's best to have oil level at the rivet right below the add mark. When hot it has room to expand. I ran mine right at the full mark and it would push oil into the gear box. This was on a 963 but basically the same setup. If your gear box is over full it could push past the seals into the dead area of the starter. Both the gear box and drive pumps are pressure systems I've been told and if over full don't have enough expansion room. If I wrong someone please correct this. I see you are in Mo. also, not alot of these machines around.
It is not engine oil. We did add hydraulic to both a while back. It later developed the leak. Checked the fluid levels recently and the drive pumps were low. The gear box (I assume this is the next section toward the engine) was over full by about 3 qts. I pumped the extra fluid out. So the dead area should not have any fluid, correct?
If this problem didn't happen till after you topped off all the oils I feel that you probably filled the sight glass to the full mark. This caused pressure to push oil into the gear box which intern pushed past the orings into the bell housing area. I've done it but didn't push oil into the dead area. Try having the sight glass at the low mark and the gear box in the middle of the safe mark. Check all when cold. If this doesn't solve the problem you have some seals gone bad.
Should these levels be checked with engine off or at low idle?
Off cold. Just do it the same as they will change some from hot to cold.