i have a bobcat excavator and i recently had to replace the pump coupler because the previous owner replaced the pump and coupler, but didnt replace the pump gear so it slipped back on the pump shaft due wear and stripped out the end of the coupler. i mostly removed the pump to remove the coupler and now after everything is back together, i still get an occasional pump groaning sound and there is clearly air in the system. i used traveler iso 46 fluid and donaldson filters and ive never had a problem before with either. i ended up changing the fluid out again for 5 gallons of iso aw 68 and i used about 2 gallons of the old fluid that came in the machine since it was clean and known to not be an issue--and it's a little better, but im still getting aeration and pump groaning sometimes. ive checked over my work, everything is tight. i drained all fluid and removed both suction hoses to be able to sneak the pump out of the way to replace coupler..i used shaving cream and soap and water to look for suction leaks and i dont see anything. im really out of ideas and it's really frustrating using the machine, because i dont want to kill the pump if there's aeration. thanks
I don't know the specifics of your machine, but what I do know about Bobcat, both excavators and skiddys, their hydraulic system design does not use a "return to tank" hydraulic flow. Instead, they design their system as a loop return to the pump, the reservoir (hyd tank) only serves to "feed oil to or relieve excess oil" from the loop as cylinders are extended and retracted. My point is, if you've opened up the loop, suction hose or pipes, replace hoses, etc, and introduce an air pocket in the loop, since it's not a "return to tank" system, it takes time for those air pockets, and the foam, to work out, but they typically do. And no, there's no way to bleed the system to speed this up. Aside from that, if you are getting air ingress in the system, and have verified the suction hoses and piping are secure and sealed, the most common culprit of air ingress is the pump shaft seal. I know you stated the previous owner replaced the pump, but that can still be a fault. Lastly, I don't know what the Bobcat oil spec is. All manufacturers have their "house blend special rocket science oil", but they don't give specifics of that oil because they want you to buy theirs. But I really would be surprised if the Bobcat oil spec'd AW68, unless you're in a really hot climate. But I could be wrong.
I used aw68 because bobcat has 2 fluids red and blue and red is for warmer climates and is aw68. it says it is compatible. it's a little thicker. im assuming blue is aw iso 46. i figured it cant hurt, especially when i am beating this **** out of this machine around the property. today it was barely groaning at all, but i did notice fluid still coming out of the reservoir cap and dripping down the reservoir. im going to replace the cap. thanks for the reply. im gonna be using it again tomorrow, but today was almost 70 degrees out and tomorrow is going to be 35, so we'll see if it still groaning. hopefully maybe the air has worked it's way out. One thing i did notice is it ALWAYS groans when you use the thumb with out with out a load. everytime, even if only for a few seconds.
What model Bobcat do you have?
it's a 2005 341G.
I wouldn't think the oil for cooler climates would be AW46. AW32 would make more sense. I also think when they refer to warm climates it's where temps. are regularly 90F and above. 70 is a pretty normal temperature where AW32 is specified for a lot of machines.
Drat, I don't have any diagrams on a 341 G series. I do have diagrams on a 331/334 G series and those models used two variable displacement pumps with a return to tank system.
am i alright to leave it in? should i get some aw32? it seems to work good. i might bend over and just get the bobcat fluid. i noticed fluid is coming out of the cap and dripping down the reservoir.
i have the service manual, what kind of diagram are you referring to? any thoughts on the fluid coming out of the hydraulic cap and dripping down the reservoir?
It's probably OK to leave the 48 oil on if it was mixed with thinner oil. If oil is coming out the cap sounds like the reservoir is over filled. There has to be room for expansion as the oil gets warm.
alright, thanks. after the machine runs for a long while and i loosen the cap, there is usually a lot of pressure inside the tank that gets released. is this normal or is the cap not venting properly?
Yes, it's normal to have some pressure in the hydraulic reservoir. It gives positive pressure to the pump inlet.
The hydraulic schematics for the machine, that's the road map on how the hydraulics work and the components involved, pumps, valves, how the oil flows, etc. It's not normal on any machine for oil to be leaking from the reservoir cap, something is wrong. Faulty cap, reservoir overfilled, or hydraulic system fault. I can't say for sure what type of cap that Bobcat used on the 341G system, but as Welder Dave stated, it's normal to have pressure release when you open the cap. That is by design to put positive pressure on the reservoir oil to feed the pump(s) and to prevent water and dirt ingress like what happens with a vented system. To cut to the chase. If you come out first thing in the morning with the machine cold, and in the proper stowed position to check the oil level in the reservoir. If that oil level is where it should be, and during the day as the machine and oil warm up to operating temperature, if you're puking oil from the cap then there's something wrong with the hydraulic system. And if it continues to show air bubbles in the oil, then you have air ingress from either the suction lines/hoses or you have a faulty pump. Nothing else will cause this. Once oil leaves the pumps it's under pressure, there's no way for air to ingress a system under pressure, rather, you'd have an oil leak.
alright, thanks. i believe the oil should be at the top of the sight glass/ball at the top?
Cold, and machine stowed in proper position for oil level check, the ball should be at mid point of the glass. If you have it at the top, there is the possibility that it's overfilled. After all, if it were at the top, and you, for whatever reason, added more oil, you wouldn't be able to tell because the ball is already at the top. Mid point gives you a better and more accurate perspective.
Oil expands with heat and oils today seem to expand more that oils used twenty years ago. As willie59 says level no higher than mid point in the glass. I don't worry about it with oil visible just above the bottom of the glass. What kind of cap do you have on the tank. Much of equipment today uses a cap meant for a radiator. If that is what you have, replace it with one from the manufacturer. Also check the seating area for the cap. Lots of times people adding oil in the field bang up the latching ring or the sealing surface.
thanks for the replies. finally after like 10 days of using the machine almost every day for a while, it seems like the groaning has mostly pretty much stopped now. i think im going to leave the aw68 in there for now. there was also a little too much in there, so i took some out.