A reader asks: I have been using ATF in the front differential of my 2012 Polaris Sportsman 400HO for a while now. I see Amsoil now has specific fluid for Polaris front ends with the Hilliard clutch set-up. Is it OK to keep running the automatic transmission fluid?
Answer: While we know that some Polaris owners with the Demand Drive 4X4 front differential system do use all-purpose automotive ATF, it might not be the best option. Automatic transmission fluid may have acceptable frictional properties to help your 4X4 clutch system engage and disengage in a satisfactory fashion, but it may be lacking in terms of long-term wear control.
Hilliard Corporation supplies the front drive system for your Polaris (and some John Deere Gator models). This front differential contains an electrically actuated clutch that engages and provides power to the front wheels whenever the rear wheels lose traction. The system disengages when the rear wheels regain traction.
Hilliard originally recommended a tractor transmission/hydraulic oil for this differential with viscosity of 9.3 cSt at 100°C. AMSOIL designed their Synthetic ATV/UTV Front Drive Oil for Polaris Demand Drive Systems to not only have the proper additives, frictional properties and wear control; its viscosity is also precisely 9.3 cSt at 100°C. A typical ATF for automotive use is in the 6.0 to 7.5 cSt range at 100°C. This means that automatic transmission fluid is considerably thinner than the viscosity suggested by Hilliard.
So while ATF may work, it is not an ideal replacement oil for your Polaris Demand Drive 4X4 system.