Vehicles from riding lawnmowers to bulldozers use hydrostatic transmissions, which require their transmission fluids changed on a regular basis. While the suggested maintenance differs from vehicle to vehicle, there are a few general guidelines and tips that work in most situations. The most important thing is to change the oils at the recommended mileage or usage points, since this move will help ensure the transmission lasts for its expected lifetime.
Look at your vehicle's maintenance guide and change your hydrostatic fluid based on the suggestion of your vehicle's manufacturer. For smaller vehicles such as riding lawnmowers, this could be as frequently as every hundred miles of use. On the other hand, a typical car doesn't need its first hydrostatic change until the 60,000 mile mark. Determine the requirements of your vehicle and keep track of the changes in a notebook.
Purchase the appropriate hydrostatic fluid for your vehicle. Some vehicles require a specific weight of oil, or the manufacturer suggests against using so called "clean" hydrostatic oil substitutes. Using an incorrect oil can not only increase the frequency of oil changes, it can also potentially damage your transmission.
Place a large container under the transmission drain plug, then loosen and remove the plug. The oil will drain into the container, which can be disposed of according to local or state state environmental regulations. Allow the oil to completely drain out of the transmission, which may take as much as 30 minutes.
Change your hydrostatic filters at the same time you change the oil. No matter the type of vehicle, there are also going to be at least one or two filters that should be changed each time you change the oil. Changing the filters will help filter impurities from the oil, protecting the transmission and lengthening the life of the oil. Typically the filters are located in a place that is easy to reach at the same time you are changing the oil.
Reattach the drain plug and fill the transmission with the required amount of hydrostatic fluid. It's recommended to leave the container in place below the transmission, in case there is an unexpected leak. Once the oil is added, check to make sure the filters are properly in place and that no oil is leaking at those locations.
Examine the transmission as you're changing the oil to see if are any of the gaskets leaking or if there is physical damage to the casing of the transmission. This is a good time to look closely and perform other needed maintenance while you are already changing the oil and filters.
Take your vehicle for a test drive once you've completed the oil and filter change. Run the vehicle for a bit and then carefully examine the transmission and other linkages to see if there are any leaks or unusual noises or rattles. Odds are any problems you find now are minor, but could turn into something serious if left untreated.
