Thank you for choosing Toro Hyper-Oil. It is an excellent replacement for the Mobil 1 oil. It is always best practice to minimize the mixing of the old oil with new oil, especially when maintaining a hydraulic system. When draining the old oil from your hydraulic system identify the oil condition to determine if a flush is needed. Whenever oil has a fowl odor, dark brown to black color, silver appearance, or a creamy color (may indicate moisture)than the hydraulic system should be flushed. When oil contamination is not identified than just draining the oil without a flush should be sufficient.
The model number is not identified but the Toro Z Mower hydraulic system can be gravity drained by removing both hydraulic lines at each wheel motor. When the hydraulic filter is removed this should drain the filter head and connecting hydraulic lines. Prior to connecting the hydraulic lines back to the wheel motors you can add the Toro Hyper-Oil. This will provide a gravity flush from the reservoir up to the wheel motors. The wheel motors are the only components with any significant amount of old oil in them. Depending on the condition of your old oil you will have to decide if the wheel motors should be flushed of the old oil or not.
When reinstalling the wheel motor hydraulic lines, inspect the o-rings on the hydraulic fittings to assure they are in good condition or replace as necessary. Install a new Toro hydraulic filter also.
-The Toro Company