Hydraulic Oil Vs. ATF

[JamLazyAss]

I was running a commercial mower today when a line loosened and dumped the hydraulic oil.
I fixed the line but had no oil.
A guy nearby told me to go ahead and fill it with ATF. Says it's the same thing anyway.
So I gave it a try.
Works like a charm.

Is there a difference between the two oils, and if so what is it?
Can I leave the ATF in it or should I drain it and replace with hyd oil?

[96dynabagger]

The definitive answer should come from the pump and hydraulic motor manufacturer as those are
the parts that will be damaged by improper substitutions.  It should at least work in a pinch.

I suspect they are very similar, but ATF will have added friction modifiers in it for use with
a clutch pack. 

[verson22]

I'd drain and refill with the correct fluid, those are two different animals.

[IBARider]

I've been around a lot of hydraulics and ATF comes standard in many systems and I would have no qualms whatsoever using it where hydraulic fluid was once used.  It's all bout 10w.  Heck, that's all I've ever put in Power Steering sytems too no probs and I've seen millions of miles... I've been in the auto and heavy equip industry over 30 years

You have to be familiar with your equip too, if there's no brake or clutch discs in the system, you're good to go.  Tranny fluid has a lot more detergents in it, but your hyd system better be clean to begin with.........