Bobcat Hydraulic fluid foaming and coming out breather cap

63 caveman · Oct 30, 2018

Just what the title say's "Hydraulic fluid foaming and coming out breather cap". It's a T250 Bobcat serial # 525613153. I plan on starting with a hydro filter and fluid change but think it may be more complicated than that. It foams with drive motors or lift functions should I look for air leak in suction lines? I have read that you should only use bobcat fluid but have used AW32 in this machine (but have not had this problem in the past) could this cause this problem?

Tones · Oct 30, 2018

The oil is unlikely to be the cause. Check the suction lines first or even bite the bullet and replace them.

63 caveman · Oct 30, 2018

Thanks Tones, just what I want to do being they are so easy to get to! just kidding if that is the problem I should be able to get it done in less than a day. Hope I don't have to pull pumps or engine.

63 caveman · Oct 31, 2018

OK I can not find anything wrong with the suction side of pump or tank. Also when raising the bucket the lift arms are jittery, dose that mean anything to anybody?
Edit- Also the "Bob Tac" coils are not plugged in and have bin disconnected for years.

Delmer · Oct 31, 2018

The jittery lifting means there's air getting into the suction side of the pump.

Tones · Oct 31, 2018

63 caveman said:
OK I can not find anything wrong with the suction side of pump or tank. Also when raising the bucket the lift arms are jittery, dose that mean anything to anybody?
Edit- Also the "Bob Tac" coils are not plugged in and have bin disconnected for years.

Did you check the hose clamps? As Delmer says. There is 2 ways of getting air in oil, low oil level or through the suction line which includes everything from the tank to the pump. A hole in the hose can be so small it won't let oil out but is big enough to let air in. Also old hose will bake hard with heat and age, loses the ability to flex, next thing foamy oil.

63 caveman · Nov 1, 2018

Thanks for replying, I ordered a new suction hose and will change that in hope you are right. I will let you know how it works out.

Delmer · Nov 1, 2018

If you take the pump out, take a good look at the seal on it also.

63 caveman · Nov 2, 2018

Another thought I have is even though it is holding 400 psi ( or more) of charge pressure but maybe not enough flow to keep drive pumps from cavitating. It is not winning or squealing or running hot.
Do any of you know where the charge pressure sensor is tapped into the system?

Lineman455 · Jul 11, 2019

63 caveman said:
Thanks for replying, I ordered a new suction hose and will change that in hope you are right. I will let you know how it works out.

Hi caveman i have the same problem on my t300 did the new suction hose fix the foaming?

63 caveman · Jul 12, 2019

Lineman455,
The short answer is no. The customer had a t250 that he had given up on and was going to scrap it but I was able to get it repaired and running for him.
I found out later that the t300 had had drive motor replaced 100 hrs before and they ran it with no case drain filter for a bit (10 to 15 hrs). He was willing to put the money in it to try to get it fixed but I didn't think it was worth it, last I heard it was tore down and abandoned by another mechanic. I have too much work to take on that headache!

Sorry I should have posted this a long time ago but I have been swamped.

Lineman455 · Jul 12, 2019

Thanks for the reply.. ive noticed a seal on top of the hydrostat pump is leaking down the back side of the pump . Ill get a new seal in that . Do u think that would cause the fluid to foam up? .

63 caveman · Jul 14, 2019

Hard to say from here

What is you charge pressure running at? You can also try capping the discharge lines on drive pumps and motors one at a time to see if that changes the foaming.

Welder Dave · Jul 15, 2019

After doing some research on the type of oil to use in skid steers after replacing a wheel motor, standard AW type hyd. oil is not recommended for hydrostatic transmissions. Bobcat also stopped recommending 10W-30 motor oil in the hyd's in 2006. Most UTTF tractor fluid is 10W-30 and is approved for hydrostatic transmissions or the Bobcat oil is what should be used. If there's that much foaming, I'd think air is getting in somehow too or the fluid is low and a return line is above the fluid level causing the foaming.

Lineman455 · Jul 15, 2019

Thanks for the reply. Ill just changed the seals on top of the hydros and case drain filter which had a few small shavings in it . Ill replace the aw46 with bobcat hydrostatic oil and see if its better .

Welder Dave · Jul 15, 2019

Here's some info.

Welder Dave · Jul 15, 2019

I was in a Bobcat dealer today and 18.9L of their oil was $118.00. I bought premium UTTF that was a full 20L for $75.00 so it is quite a bit more expensive. I guess see what it does after you change the seals and then decide if you want to spend for the Bobcat oil.

Lineman455 · Jul 19, 2019

I changed the seals on top of the hydrostatic drive . Filled it with tractor supply traveler premium uviversal tractor fluid . And it doesnt foam anymore ..works great now . Thanks everyone !

Lineman455 · Jul 19, 2019

Oh and changed case drain filters . They looked clean except for a handful of very small slivers of metal. Is that cause for concern?

FlatTire · Nov 14, 2020

I’m having a foaming issue on my Bobcat 753. I’ve been assuming it’s pulling air on the suction side, but haven’t found the issue yet. Lineman455 are you referring to the seals on top of the actual hydro pump, or the drive motors at the wheels? Just trying to clarify. Seems that’s a good place for me to start if it fixed your issue.

Bobcat Hydraulic fluid foaming and coming out breather cap

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