Boss Hydraulic Fluid should be replaced at the beginning over every season as well as during the season depending on the amount of use. As part of general maintenance of your Boss Snowplow, it is recommended that your change the hydraulic fluid once per season. Boss High Performance Hydraulic Fluid is specially formulated to maintain its viscosity from normal use to as low at -40 degrees Fahrenheit. We carry our own High Performance Plow Fluid which is the exact concentrate as Boss’s own hydraulic fluid but for half the price. Check them all out below and buy now to keep your plow in working condition.