Question: Motor Oil for Backhoe Fluid?

California · Feb 24, 2021

My 1980's backhoe specifies 303 UTF. I use J20C, the later multigrade UTF.

I just discovered the fluid must have gotten water in it, its creamy foam and squeals easily. Its time to flush and replace it.

I have a few 2 gallon jugs of NAPA's prior spec 15w40 diesel oil, made obsolete by recent smog gear. It was on closeout real cheap and my 40 year old tractors don't care.

Is this diesel rated motor oil suitable to flush the backhoe's hydraulics, and is it harmless run it for the season before buying more J20C?

I also have an unopened gallon of Dexron III ATF. Suitable for flushing oil? For blending?

I'm assuming all these fluids are nearly identical, with likely extreme pressure additive in the UTF that isn't crucial for a backhoe, and other magic in the diesel oil that's also not relevant. I guess the question is whether there's anything harmful.

LittleBill21 · Feb 24, 2021

my white lawn tractor uses 20w50 motor oil for the hst transmission. do with that what you will

3Ts · Feb 24, 2021

I have one hydraulic system from the 70's that specifies SAE 30 wt motor oil so I would think you could. HOWEVER, I would be concerned about the compatibility of the oils. I use the same oil to flush a system that it uses so I don't have to worry about the oils being compatible with each other.

California · Feb 24, 2021

3Ts said:
... I would be concerned about the compatibility of the oils. I use the same oil to flush a system that it uses so I don't have to worry about the oils being compatible ...

Yeah that's my concern.

I was surprised after a little research to see that some varieties of UTF sold in Britain and Australia are universal, the same product is recommended for motor oil as well as hydraulic and transmission fluid.

i7win7 · Feb 24, 2021

Bush hog 750 3pt backhoe w/pto pump recommends 30w non detergent engine oil.

Tractor Seabee · Feb 24, 2021

Before HSTs came along the common hydraulic fluid was motor oil. Very old tractors used the engine oil sump as the hydraulic system sump also. UTFs are in the range of 30W oil.

Ron

LD1 · Feb 25, 2021

I would have no hesitation using 15w40 in an old backhoe. Or the ATF, or a mix for that matter.

Think about the moving parts. Gear pump....valve, cylinders.....thats pretty much it.

Transmissions have gear pumps, hydraulic pistons, spool valves, etc.
Engines have gear pumps....seals...sometimes little pistons for tensioners, etc.

A simple old hydraulic system with a pump, valve, and cylinders is about the LEAST demanding application you can ask of an oil.

California · Feb 25, 2021

LD1 said:
I would have no hesitation using 15w40 in an old backhoe. Or the ATF, or a mix for that matter.

Think about the moving parts. Gear pump....valve, cylinders.....thats pretty much it.

Transmissions have gear pumps, hydraulic pistons, spool valves, etc.
Engines have gear pumps....seals...sometimes little pistons for tensioners, etc.

A simple old hydraulic system with a pump, valve, and cylinders is about the LEAST demanding application you can ask of an oil.

Thanks. That was my reasoning. Hydraulic oil mostly just pushes cylinder pistons, an undemanding application. But I wondered if anyone would comment on incompatibility between the various fluids. So far, I haven't seen anything that discourages me from going ahead with this.

i need to put something fresh in there. And until I've had my covid shots it seems like a good idea to use materials already on hand instead of going shopping.

Cycledude · Feb 25, 2021

In a hydraulic system I wouldn’t attempt using any oil that’s not approved, I actually know someone that changed the oil and used motor oil instead and very soon wound up having to buy a new pump.