Hydraulic oil leaking from air filter housing

[Planedriver]

So I quit drinking for the past three days to be sure I am seeing what I see. Yep, I have clean hydraulic oil leaking from the air filter housing on my Hitachi UHO83.

The machine smokes a little more than it should on startup but then clears up. When I shut down, hydraulic oil starts dripping in a pretty good stream and will run about a quart on the ground then in a few hours it stops. I don't get it! How is this happening? Turbos?

 

[Delmer]

Just guessing of course... some hydraulic tanks are indeed pressurized by the turbo, so the oil could push back to the air filter via the turbo explaining all of your problems. If that's the case it should be possible to trace the plumbing and determine if there's a check valve in there that's got some junk in it keeping it from sealing. Possibly your hydraulic oil is contaminated with moisture or something else that is causing it to foam, contributing to overflowing/backflowing.

 

[Planedriver]

Thx Delmer. I'll give it anther look but the hyd tank is pressurized primarily from a pump on the back of the alternator. Of course the turbo could be hooked up to the tank also (the oil is coming from somewhere). As far as the oil..... Just changed it and used Mobile that meets spec and is recommended in the Hitachi manual.....

 

[lantraxco]

Too much hydraulic oil in the tank maybe, or more likely a check valve not working properly. The hitachis I worked on had small compressors driven off something mechanically, they pulled clean air from the air cleaner though to keep the hyd oil uncontaminated, so you can see how something bleeding back would give you the problem you're seeing. look for a line from your little alternator driven pump to the intake someplace, and also on the line from that pump to the hyd tank, look for a check valve. As I recall and it's been thirty years, the oil should be in the middle of the glass with everything tucked up tight and the boom laid down until the links touched the ground? YMMV. Too much oil will cause a loss of tank pressurization during work cycles which leads to pump growlies due to cavitation.

 

[Planedriver]

Too much hydraulic oil in the tank maybe, or more likely a check valve not working properly. The hitachis I worked on had small compressors driven off something mechanically, they pulled clean air from the air cleaner though to keep the hyd oil uncontaminated, so you can see how something bleeding back would give you the problem you're seeing. look for a line from your little alternator driven pump to the intake someplace, and also on the line from that pump to the hyd tank, look for a check valve. As I recall and it's been thirty years, the oil should be in the middle of the glass with everything tucked up tight and the boom laid down until the links touched the ground? YMMV. Too much oil will cause a loss of tank pressurization during work cycles which leads to pump growlies due to cavitation.

Really good info. I spent some time tinkering yesterday and found a couple of wires "North" of the valve body, near the table that were broken. With many contorted maneuvers I was able to splice them back. (I figured, since the auto idle is inop they were the culprit.) I also checked as much wiring as possible and found a sensor attache to two small hydraulic lines near the counterweight had come unplugged and corrected that. (I think there is a valve in line with the air pluming you are talking about that may not have been getting power and causing the problem?)

The short story is; The auto idle still is inop but I now have one red light on each of two magnetic sensors on the valve bodies that weren't illuminated before. The hydraulic "feedback" seems to have stopped for now. I'm about to go out and fill the hydraulic oil and see what happens.

I'll keep you all posted as it goes in case someone else with one of these dinosaurs has the same problem in the future.

 

[Planedriver]

I gave up and put a 3/8" check valve in the line going to the air filter. Been running the machine for a couple of weeks now and no problems.