flushing hyd fluid

[mikeb]

how do you flush the entire hyd system on a 873? someone put diesel about two gallons and it wiped out the seals on the lift/tilt spool, just got done replacing the seals and I want to know if there was a good way to flush the system safely?

 

[bobbie-g]

mikeb, I'm not the expert. When I got my T180, the hydrostatic fluid was green and ugly. Per suggestion from Ken and Tazza, I used the aux hydraulic function to pump fluid out through a hose connected to the aux connector on the lift arms. Pumped all that wouldl come out (about 6 gallons out of the 8.5 total it holds), then I refilled 3 times with 10W30 oil and exercised all the drive and hydraulic functions, then the last time I refilled with genuine Bobcat hydro fluid. I think I got out all but a few percent of the old gunk. It's expensive to fill up with 6 gallons of oil each time, but it was worth it to me to get it clean. ---RC

 

[Tazza]

mikeb, I'm not the expert. When I got my T180, the hydrostatic fluid was green and ugly. Per suggestion from Ken and Tazza, I used the aux hydraulic function to pump fluid out through a hose connected to the aux connector on the lift arms. Pumped all that wouldl come out (about 6 gallons out of the 8.5 total it holds), then I refilled 3 times with 10W30 oil and exercised all the drive and hydraulic functions, then the last time I refilled with genuine Bobcat hydro fluid. I think I got out all but a few percent of the old gunk. It's expensive to fill up with 6 gallons of oil each time, but it was worth it to me to get it clean. ---RC

Its really the only way. You have oil trapped in the cylinders, pumps, motors, oil cooler and hoses. You will never get it all short of pulling the machine to bits.
That way works for me, i have done it a few times to get water out of the system.

 

[BobcatofDuluth]

mikeb, I'm not the expert. When I got my T180, the hydrostatic fluid was green and ugly. Per suggestion from Ken and Tazza, I used the aux hydraulic function to pump fluid out through a hose connected to the aux connector on the lift arms. Pumped all that wouldl come out (about 6 gallons out of the 8.5 total it holds), then I refilled 3 times with 10W30 oil and exercised all the drive and hydraulic functions, then the last time I refilled with genuine Bobcat hydro fluid. I think I got out all but a few percent of the old gunk. It's expensive to fill up with 6 gallons of oil each time, but it was worth it to me to get it clean. ---RC

I've said it before and I'll say it again, you don't want to use your auxillary hydraulics to pump out the hydraulic fluid. Doing so runs your pump dry, which is very bad for it.
No disrespect to you, bobbie-g, or Ken and Tazza, but this is possibly some of the worst advice on changing hydraulic fluid, and shouldn't be given unless you want to deal with the wrath of someone following your suggestion and having to spend upwards of 5 grand on a new pump set.
Follow the service manual for the correct procedure. If you don't have a service manual, now would be a good time to get one.

 

[Tazza]

I've said it before and I'll say it again, you don't want to use your auxillary hydraulics to pump out the hydraulic fluid. Doing so runs your pump dry, which is very bad for it.
No disrespect to you, bobbie-g, or Ken and Tazza, but this is possibly some of the worst advice on changing hydraulic fluid, and shouldn't be given unless you want to deal with the wrath of someone following your suggestion and having to spend upwards of 5 grand on a new pump set.
Follow the service manual for the correct procedure. If you don't have a service manual, now would be a good time to get one.

Surely the drive pumps would never be run dry unless you cracked a drive motor line and operated the drive circuit. Sure, there would be reduced oil in there but it would still be lubricated. As for the gear pump, you will still have residue, i would suspect there would be even more oil in there than there would be when installing a new component?

 

[jerry]

Surely the drive pumps would never be run dry unless you cracked a drive motor line and operated the drive circuit. Sure, there would be reduced oil in there but it would still be lubricated. As for the gear pump, you will still have residue, i would suspect there would be even more oil in there than there would be when installing a new component?

I think you are right on that Tazza, the drive pumps would not lose their oil through the aux couplers.

 

[BobcatofDuluth]

Surely the drive pumps would never be run dry unless you cracked a drive motor line and operated the drive circuit. Sure, there would be reduced oil in there but it would still be lubricated. As for the gear pump, you will still have residue, i would suspect there would be even more oil in there than there would be when installing a new component?

Running the hydraulic reservoir dry leads to cavitation, premature pump wear and eventually failure. Granted, most of the damage will be in the hydraulic pump and not the hydrostatic pumps, but those also have moving parts that rely on that hydraulic fluid for proper lubrication even when the drive system isn't being operated.
The hydraulic pump is gravity fed from the reservoir and will run DRY following the procedure in question. There is another variation of this method I've heard of backyard mechanics using, but that also leads to cavitation and premature pump wear. It can't be done safely.
Bottom line, pumping the hydraulic fluid out through the auxillary quick coupler is NOT the manufacturer's recommended service procedure. Before anyone thinks about following that advice, I'd highly recommend consulting a service manual. Risk of component damage is far too high.

 

[bobbie-g]

Running the hydraulic reservoir dry leads to cavitation, premature pump wear and eventually failure. Granted, most of the damage will be in the hydraulic pump and not the hydrostatic pumps, but those also have moving parts that rely on that hydraulic fluid for proper lubrication even when the drive system isn't being operated.
The hydraulic pump is gravity fed from the reservoir and will run DRY following the procedure in question. There is another variation of this method I've heard of backyard mechanics using, but that also leads to cavitation and premature pump wear. It can't be done safely.
Bottom line, pumping the hydraulic fluid out through the auxillary quick coupler is NOT the manufacturer's recommended service procedure. Before anyone thinks about following that advice, I'd highly recommend consulting a service manual. Risk of component damage is far too high.

BobcatofDuluth: We all offer our suggestions here. Yours differs from mine. I believe you have a lot more understanding of these things than I do, and I appreciate your perspective and your posts. I would certainly agree that using the aux pump to empty the hydro reservoir is not in the manual. But it's fast, easy, and simple. I would offer this to you and to others: given the stated concern about pumping all the oil out via the aux connector, one could stop when there was a half inch or more left in the bottom of the reservoir. That way the pump would always have oil, and nearly as much old oil would be drained as popping the fitting loose at the bottom of the reservoir. And it would be a whole lot faster and a whole lot less messy and a whole lot easier. Just my perspective. ---RC

 

[BobcatofDuluth]

BobcatofDuluth: We all offer our suggestions here. Yours differs from mine. I believe you have a lot more understanding of these things than I do, and I appreciate your perspective and your posts. I would certainly agree that using the aux pump to empty the hydro reservoir is not in the manual. But it's fast, easy, and simple. I would offer this to you and to others: given the stated concern about pumping all the oil out via the aux connector, one could stop when there was a half inch or more left in the bottom of the reservoir. That way the pump would always have oil, and nearly as much old oil would be drained as popping the fitting loose at the bottom of the reservoir. And it would be a whole lot faster and a whole lot less messy and a whole lot easier. Just my perspective. ---RC

What would you suggest as a fool-proof method of knowing when to shut the machine off before the tank is empty? Sight glasses and dipsticks are at the top.

 

[bobbie-g]

What would you suggest as a fool-proof method of knowing when to shut the machine off before the tank is empty? Sight glasses and dipsticks are at the top.

My T180 has a bung on the top of the reservoir. If I wanted to know what the level was, I'd stick something into the port and see how much was left in it. ---RC

 

[Skid Steer Guy]

What would you suggest as a fool-proof method of knowing when to shut the machine off before the tank is empty? Sight glasses and dipsticks are at the top.

Now you have me wondering... How would you do this Bobcat of Duluth? Would you strip the machine down? What is the answer??

 

[gtstang462002]

Now you have me wondering... How would you do this Bobcat of Duluth? Would you strip the machine down? What is the answer??

When I flushed diesel out of a hydraulic tank a few weeks ago I used the aux hydrualics. When it started pumping air bubbles I shut it down and refilled the tank, moved all of the hydraulics and repeated. 15 gallons of hydraulic oild later and it looked and smelled like hydraulic oil.

 

[skidsteer.ca]

When I flushed diesel out of a hydraulic tank a few weeks ago I used the aux hydrualics. When it started pumping air bubbles I shut it down and refilled the tank, moved all of the hydraulics and repeated. 15 gallons of hydraulic oild later and it looked and smelled like hydraulic oil.

Bobcat of Duluth makes a valid point , you don't want to operated the system with air in it. By that I mean you want to keep the pressure in the system to a minimum while there is air inside, and keep this period of operation as short as possible.
Because making the pump come to high pressure while sucking in a mixture of oil and air is very hard on any pump. as is continuing to run a pump without a steady, unrestricted supply of clean oil.
But if I understand this correctly, pumping the oil out at low pressure and immediately shutting the machine off when air begins to come out, once every 1000 hours of operation, is not going to hurt anything imo.
When the system is refilled, and the engine started the pump will produce the "charge pressure" of 100 to 200 psi depending on the machine, and this will purge most of the air in the charge pressure loop.
Then it would be a good idea to loop the front couples together and operate the auxilary hydraulics in one direction to purge that loop.
Last would be the drives, which should have a minimum of air anyway, because this system was not drained. (unless you tried to drive the machine while the reservoir was low or empty. But blocking the machine up and rotating the tires in one dirrection would purge any air that was in that circuit. The blocking would be done to let the tires turn while keeping the pressure low in that system.
By this point the machine should be operating normally and there abnormal sounds of air in the system should be long gone. I would still suggest a leisurely drive around in as straight a line as possible, while raising and lower the boom, (but not hitting the cylinders ends) again to further work the system at low pressures and give the air a change to get back to the reservoir and rise to the top. Letting the machine sit between these cycles to give air in the reservoir a chance to surface would be a good idea also.
I don't see how this would be any different then blowing any of several hoses on the machine that could allow all the reservoir oil to be lost. At which point the hose would be fixed and the machine put back to work. Hopefully, in the same gentle manner at first.
With that said it would be a good idea to consult the service manual for your particular machine and see what instruction are offered there. In my experience, the manufacturer usually takes the utmost care in protecting the machine for many reasons, but also because the servicing is usually not at their expense. They also assume it is being done in a perfect shop environment. Some of their steps may not be pratical in the field. But the owner should carefully consider the pros and cons, as they are paying the bill.
Ken

 

[magnetorque]

Bobcat of Duluth makes a valid point , you don't want to operated the system with air in it. By that I mean you want to keep the pressure in the system to a minimum while there is air inside, and keep this period of operation as short as possible.
Because making the pump come to high pressure while sucking in a mixture of oil and air is very hard on any pump. as is continuing to run a pump without a steady, unrestricted supply of clean oil.
But if I understand this correctly, pumping the oil out at low pressure and immediately shutting the machine off when air begins to come out, once every 1000 hours of operation, is not going to hurt anything imo.
When the system is refilled, and the engine started the pump will produce the "charge pressure" of 100 to 200 psi depending on the machine, and this will purge most of the air in the charge pressure loop.
Then it would be a good idea to loop the front couples together and operate the auxilary hydraulics in one direction to purge that loop.
Last would be the drives, which should have a minimum of air anyway, because this system was not drained. (unless you tried to drive the machine while the reservoir was low or empty. But blocking the machine up and rotating the tires in one dirrection would purge any air that was in that circuit. The blocking would be done to let the tires turn while keeping the pressure low in that system.
By this point the machine should be operating normally and there abnormal sounds of air in the system should be long gone. I would still suggest a leisurely drive around in as straight a line as possible, while raising and lower the boom, (but not hitting the cylinders ends) again to further work the system at low pressures and give the air a change to get back to the reservoir and rise to the top. Letting the machine sit between these cycles to give air in the reservoir a chance to surface would be a good idea also.
I don't see how this would be any different then blowing any of several hoses on the machine that could allow all the reservoir oil to be lost. At which point the hose would be fixed and the machine put back to work. Hopefully, in the same gentle manner at first.
With that said it would be a good idea to consult the service manual for your particular machine and see what instruction are offered there. In my experience, the manufacturer usually takes the utmost care in protecting the machine for many reasons, but also because the servicing is usually not at their expense. They also assume it is being done in a perfect shop environment. Some of their steps may not be pratical in the field. But the owner should carefully consider the pros and cons, as they are paying the bill.
Ken

bobcat of Duluth, I agree with you and ken from the previous post, when in doubt, follow the manufacturer's specifications. However, I have a concern. I am working on a bobcat 843 and I have a similar problem, the hydraulic fluid has been contaminated and I need to flush the system. I have the bobcat service manual, and have reviewed it thoroughly and have not found any instructions on how to flush out the entire system. The process is mentioned in the trouble shooting charts as a solution to certain problems, but again, no instructions are given on how to flush the system. Any help here?

 

[Tazza]

bobcat of Duluth, I agree with you and ken from the previous post, when in doubt, follow the manufacturer's specifications. However, I have a concern. I am working on a bobcat 843 and I have a similar problem, the hydraulic fluid has been contaminated and I need to flush the system. I have the bobcat service manual, and have reviewed it thoroughly and have not found any instructions on how to flush out the entire system. The process is mentioned in the trouble shooting charts as a solution to certain problems, but again, no instructions are given on how to flush the system. Any help here?

I pump it out the quick couplers with the engine running at idle.
It is your call how to proceed though. You need to get the system clean.
As you have noticed, there is no drain plug to drain the system.