Wrong hydraulic oil causing too much resistance in hydraulic pump?

[TimBuck2]

I have a 30 year old Gravely zero turn mower with very little time on it (about 350 hours). I finally decided to change out the hydraulic oil and filter. I used what I had on hand for oil - Walmart SuperTech tractor transmission and hydraulic oil.

It took a while for the system to fill up (judging by falling level in in the intake side of the tank).

I believe all the air pockets are gone. The machine is up on jack stands, and the wheels are turning.

However, when I tried to run them full speed there is too much resistance in the hydraulic pump, and the engine starts to die.

The manual calls for using 20W-50 oil. I can't find any info on the viscosity of the SuperTech. If I can assume it is in the ballpark of by Kubota UDT specs, I am thinking it is something like 50 on the very pleasant 70 degree day

Anyone know whether this symptom is from too the oil being too viscus, or not viscus enough?

Any ideas appreciated before I start all over and see if the right oil was the right way to do it.

Thanks, Tim

Thanks.

 

[rScotty]

I doubt if the problem is the oil. 20w-50 is a litte more viscous than what it calls for, but at room temperature it is basically a 20 wt oil and that is close enough to what you put in that it should work. If anything, I'd expect the Walmart SuperTech to be better.

No ideas other than I'd look elsewhere than the type of oil.

 

[TimBuck2]

Thanks rScotty you are correct. I drained the SuperTech and replaced with 20W-50 and, if anything, the problem is worse now.

 

[rScotty]

Maybe if you described the problem in more detail....
Has it happened before? What does "engine starts to die" mean? Won't rev? Hold revs? Backfires? Shuts off? Does it go to idle, or just stop running? And is all this with drive engaged or not.

 

[oldnslo]

Very doubtful that the oil is the problem since pressure is created by resistance to flow. Should be bo resistance with wheels in the air so suspect some problem with something mechanical binding like brakes or the engine itself.

Will the engine run full throttle without wheels turning?

 

[TimBuck2]

The hydraulics were fine before I changed the oil and filter. The new filter is OEM from a Gravely dealer (thought I will triple check the part no. today).

After refilling the system,
- the engine runs fine,
- when I engage either or both wheel hydraulic motors the engine starts to start to bog down, and bogs down from too much torque from the hydraulic system. The further I engaged either hydraulic valve, the more the engine bogs down.
- at first neither wheel would turn, once the air pockets were gone, both wheels turn but if I engage either valve further the engine bogs from too much torque from the hydraulic system, and the engine will die if I fully engage either hydraulic valve.

Each wheel has its own hydraulic pump with the valve built in.

The system has an heat exchanger for cooling.

I need to trace the system and get a handle on where all the parts sit in relation to one another.

Thanks gents,
Tim

 

[CloverKnollFarms]

My hyro doesnt use hydro oil, it uses a synthetic engine oil, as I recall, most do not use hydraulic oil. I have Parker transmissions

 

[Langanobob]

Have you tried taking it off the jack stands and running it on the ground?

 

[TimBuck2]

Have you tried taking it off the jack stands and running it on the ground?

That occurred to me, that perhaps the problem is not enough resistance against oil flow. But I have not tried it yet.

 

[dusty3030]

Parking brakes aren't engaged are they?