Doosan Chain Case Oil

I recently picked up a Doosan/Daewoo 440 Plus, and plan on changing the chain case oil in the not too distant future (since I have no idea what is in there, if anything at all, or for how long). The manual calls for Dexron III in the chain cases. Which is weird to me, because nothing like that is used anywhere else in the machine. The hydraulics give several options, most of which are along the lines of a typical tractor transhydraulic fluid. So it's not a matter of just trying to spec a common fluid- they went out of their way to call for this oddball (they don't even say something like "or AW32 hydraulic fluid" which you'd think would be a nice option to give for someone working on this type of equipment). I'm tempted to just use the same Mobilfluid 424 I'm putting in the hydraulics in the chain case- that way I don't have to buy several gallons of ATF just for this and can use what I am already buying by the pail. However, it keeps sticking in my mind- why would they spec this fluid just for that- is there some performance requirement that I'm missing? It's not like ATF is especially cheaper than hydraulic fluid. The only obvious answer is they want the lower viscosity, but why? Most skid steers seem to spec a heavier oil (like 10W-30 or 15W-40 engine oil) for the same application.

I guess I'm just curious if anyone else has run across this or has any thoughts as to whether going with the somewhat heavier hydro fluid would be an obvious issue.

Under_Pressure said:

The only obvious answer is they want the lower viscosity, but why? Most skid steers seem to spec a heavier oil (like 10W-30 or 15W-40 engine oil) for the same application.

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The desired viscosity of your chain case fluid should depend on your expected ambient operating temperature ... I am guessing that a chain case does not generate much heat. In my CAT 242B chain cases, I run 0W-40 Rotella T6 (synthetic) which according to the CAT chart is good for -40 F to 104 F (-40 C to +40 C) ... my operating temperature can go down to -22 F (-30 C). The CAT recommended chain case maintenance interval is a change every 1000 hours. When I did mine last year the old oil looked pretty clean, which makes sense since it is a closed system.

The problem with switching away from your rated oil to something different is the difficulty in removing all the old oil. It may be difficult to get the last quart or so out ... which would then mix with your new fluid. Easiest way to go is to replace it with the same fluid currently in use ... if it meets your operating temperature requirements.

Put the 424 in it. It will treat it just fine.