Hi Skot,
I have been running Evans (waterless - propylene glycol) in our plane since new (912ULS). At the time Rotax instructions indicated to use this. Since that time, Rotax has recommended both options: 100% propylene glycol - Evans waterless or Ethylene glycol 50% + 50% water.
Some folks run a little higher temps with the waterless than they do with the 50/50 ethylene glycol - the mix has a little better specific heat which helps keep the temps down and it probably has a little lower viscosity than the 100% propylene glycol.
I decided to stay with the evans as I have never had any issues with the temp; and, I like the idea of the higher BP of the Evans. The temp issues can be aircraft specific.
If you change from mix to Evans, Evans sells a flush to use after draining out the old stuff - refill with the flush, run and drain - then install the Evans.
If you go to the Evans website or maybe even Aircraft Spruce, you should be able to find current directions.
Bottom line you can use either - just follow the instructions for the one you use.
BTW - the other use of propylene glycol?.....it's an approved food additive. Often shows up in dog food as a moisture sequestrant.
Sincerely,
Dave S
KF7 Trigear
St Paul., MN